HPS SERVICING GUIDE - American Electric Lighting
High Pressure Sodium
Servicing Guide
Table of Contents
OVERVIEW .............................................................. 3
IMPORTANCE OF SAFETY ..................................... 3
INTRODUCTION TO HID LIGHTING ...................... 4
Incandescent Lamps .......................................... 4
Fluorescent Lamps ............................................ 4
HID Lamps ......................................................... 4
Mercury Vapor and Metal Halide Lamp Starting .. 6
Ballasts .............................................................. 7
Arc Tube Design ................................................ 7
HPS End-of-Life Voltage .................................... 8
TABLE 1: HPS Lamp Data ........................................ 9
HID LAMP LUMEN MAINTENANCE ........................ 9
HPS Lamps ...................................................... 10
Mercury Vapor Lamps ...................................... 10
Metal Halide Lamps ......................................... 10
HID LAMP LIFE ...................................................... 10
HPS Lamps ...................................................... 10
Mercury Vapor Lamps ...................................... 11
Metal Halide Lamps ......................................... 11
THE HPS LUMINAIRE ........................................... 11
HPS Lamp Starters .......................................... 11
Starter Operation .............................................. 11
Starter Variations .............................................. 13
Instant Restrike Starters ................................... 13
Two-Lead Starters ............................................ 13
HID LAMP BALLASTS ............................................ 14
TABLE 2: Characteristics for HID Light Sources ..... 16
Ballast Characteristics ...................................... 16
Reactor Ballasts ............................................... 16
Lag Auto Ballasts ............................................. 16
Constant Wattage Autotransformer Ballasts ..... 17
Constant Wattage Ballasts ............................... 17
HPS Mag Reg .................................................. 17
Matching Lamp and Ballasts ............................ 18
TROUBLESHOOTING ........................................... 18
HPS LAMP CYCLING ............................................. 19
Equipment Mismatching ................................... 19
Reignition Phenomenon ................................... 20
Vibration Sensitivity .......................................... 20
Thermal Cycling ............................................... 21
Photocontrol-Induced Cycling ........................... 21
HPS LIGHTING SYSTEMS .................................... 21
Test Procedures ............................................... 21
Selecting the Test Group .................................. 22
Visual Inspection .............................................. 22
Voltmeters ........................................................ 23
Neon Lamp Testers .......................................... 23
Luminous Wattmeters ...................................... 23
AN INSTALLED LOCATION ................................... 25
HPS Luminaire Failures ................................... 26
GLOSSARY OF ELECTRICAL TERMS .................. 27
APPENDIX A .......................................................... 29
I. Lamp Physical Characteristics ..................... 29
II. Lamp Electrical Characteristics
(RMS Values) .............................................. 29
III. Ballast Requirements .................................. 30
APPENDIX B .......................................................... 31
I. Lamp Physical Characteristics ..................... 31
II. Lamp Electrical Characteristics
(RMS Values) ............................................... 31
III. Ballast Requirements .................................. 32
IV. Luminaire Requirements ............................. 32
V. Socket Requirements .................................. 33
The information presented in the High Pressure Sodium
(HPS) Servicing Guide is generic in nature. It can be applied
to and used in troubleshooting and servicing all types of
HPS systems regardless of the manufacturer. The servicing
guide contains information, illustrations and data on these
same topics:
• Safety practices and equipment used when servicing
HPS and other High Intensity Discharge (HID) lighting
• Basic construction and operation of HID lamps, and
how they differ from incandescent lamps.
• Unique construction and operating features affecting
servicing. Special attention is paid to starting circuits,
ballasts and photocontrols.
• An in-depth look at the causes of the cycling ON and
OFF of the HPS lamp, including end-of-life cycling.
• Test equipment for servicing HPS lamps and luminaires,
including the drawbacks of voltmeters and neon lamp/
luminaire testers. Details on constructing and using a
highly effective, inexpensive piece of test equipmentthe incandescent lamp luminous wattmeter tester (LWT).
• Troubleshooting the HPS luminaire in the field. Step-bystep guidelines for performing a 15-minute service call
and making quick, cost-effective repair/replace decisions.
• Factors to consider and problems associated with the
installation and use of mercury vapor to HPS
conversion kits.
HID lamp servicing requires close attention to safety.
Working with electrical equipment at significant heights
can be dangerous if proper preparations and precautions
are not taken. The following is a general safety checklist.
Always follow the exact safety procedures outlined by
your company.
1. Park the lift truck at the safest possible location at
the work site. Set up safety cones to direct traffic
around the truck.
2. Before beginning, check the lift bucket of the truck
to make certain it is secure. The pivot point
mounting should be tight with no cracks or breaks.
Also make certain the bucket is equipped with a
fiberglass liner and that the liner is in good shape
with no cracks or breaks.
Although not a common problem, lamps have been
known to shatter due to operational problems or
when being turned into or out of the socket.
3. Make sure the boom strap is in place and secure.
4. Make certain the lanyard is in good shape, fastened
and secure. The safety belt also must be in good
5. Always strap on the safety belt before raising the
bucket. Putting the safety belt on should be the first
thing you do after stepping into the bucket.
6. Always use a properly secured safety belt when
working from ladders.
of each workday for holes and tears. Replace
damaged gloves immediately. Keep your high-voltage
gloves in the glove bag located in the bucket so they
will always be available when needed.
10. Always wear proper eye protection whenever you
work on luminaires or replace a lamp. Although not
a common problem, lamps have been known to
shatter due to operational problems or when being
turned into or out of the socket.
11. Luminaires can be heavy. Position the bucket so you
do not have to overreach or stretch while lifting or
handling the luminaire. Always secure the luminaire,
cover and any other items or tools inside the bucket so
there is no danger of them falling to the ground.
12. Always be certain the luminaire is properly grounded.
Use the grounding screw provided and run back to
mechanical ground. If the luminaire is not properly
grounded, it may become electrically “hot” if a
component or wire inside the housing grounds itself
to the housing. This can happen if wires become
frayed, or ballasts or other components are damaged.
The danger of electrical shock then exists when the
service technician touches the housing and grounds
another part of his or her body. The feeling of static
electricity when you are near to, or brush lightly
against a luminaire is a sign that it may be electrically
“hot.” De-energize the fixture immediately and inspect
for a possible short to ground inside the housing.
8. Wear work boots with non-slip insulating soles.
13. If a lamp (light bulb) should break during installation
or removal, de-energize the fixture and remove the
broken lamp from the socket using a broken lamp
base extractor.
9. Always wear high-voltage gloves when servicing and
replacing luminaires. Inspect the gloves at the start
14. Work carefully and use good judgment in all situations.
Most accidents are the result of carelessness.
7. Always wear a hard hat when servicing a luminaire
in the field.
HPS lighting systems are one of a group of systems
classified as High Intensity Discharge lighting. The HID
lamp group also includes all mercury vapor and metal
halide lighting systems.
The HID lamp group is one of the three major lamp
groups used in modern lighting; the others are
incandescent and fluorescent. To better understand
how HID lighting systems operate, a short review of
incandescent and fluorescent lamp operation is helpful.
Incandescent Lamps
A conventional tungsten incandescent lamp has a
tungsten filament enclosed in a glass bulb filled with inert
gases (Figure 1). When electric current is passed through
the filament, it offers resistance to the current flow. The
filament heats up and glows, producing light. As the lamp
operates, the tungsten filament evaporates and deposits
as black patches on the inside of the bulb. The inert gases
work to reduce this blackening, but cannot eliminate it.
Light output diminishes as the filament evaporates, and
the lamp eventually fails due to filament breakage.
Tungsten halogen lamps try to reduce filament
evaporation by including small amounts of bromine,
forcing the tungsten to redeposit on the filament.
Halogen lamp life is about twice that of conventional
incandescent lamps.
Incandescent lamps are available in wattages ranging
from 2 to 1500 watts and above. In many cases, the light
level generated by a particular luminaire can be increased
or decreased simply by switching to different lamp wattage.
Glass Bulb
This is because incandescent lamps are “resistance
smart.” The lamp’s filament is designed and sized to
offer a preset amount of resistance to current flow. This
controls the amount of current passing through the lamp.
On the other hand, HID lamps are “amps dumb.” They
have no built-in resistance to current flow and the lamp
must rely on an external ballast to limit current flow to
the lamp. The wattage and voltage ratings of the HID
lamp and its ballast must match exactly.
Fluorescent Lamps
Fluorescent lamps are low pressure or Low Intensity
Discharge lamps. The lamp consists of a closed tube
that contains two cathodes, an inert gas such as argon,
and a small amount of mercury (Figure 2). When
voltage is supplied to the lamp in the correct amount,
an electrical arc strikes between the two cathodes. This
arc emits energy that the phosphor coating on the lamp
tube converts into usable light.
HID Lamps
The HID lamp group is by far the most important lamp
group used in modern exterior and industrial lighting.
HID light sources are highly regarded for their long life
and high efficacy. The compactness of HID lamps also
increases optical control and allows for a great deal of
flexibility in the area of luminaire design.
HID systems are the most cost-effective method of
lighting roadways, parking areas, sports fields, signs
and buildings. HID systems also are ideally suited for
interior applications such as sports arenas,
warehouses, industrial plants and certain types of
indirect office and commercial lighting.
FIGURE 1. Typical incandescent lamp components.
FIGURE 2. Typical fluorescent lamp components.
All HID lamps share a number of design and operating
features, but there are some important differences
between mercury vapor, metal halide and HPS lamps
(Figure 3).
All HID lamps contain a sealed arc tube mounted inside
a glass bulb. In mercury vapor and metal halide lamps,
the bulb is filled with hydrogen gas, which absorbs the
ultraviolet radiation produced during operation. HPS
lamps have a vacuum inside the bulb to isolate the arc
tube from changes in ambient temperature.
As the arc tube is manufactured, small amounts of
special arc metals, such as mercury, halide compounds
or sodium, are sealed inside the tube. Starting gases,
such as argon, neon or xenon, are placed inside the
tube. The arc tube also houses the lamp’s two main
electrodes, plus the separate starting electrode used
in mercury vapor and metal halide lamps.
An HID lamp produces light in much the same manner
as a lightning bolt. But instead of a brief flash, the
electric arc between the lamp’s two main electrodes is
continuous. The striking and maintaining of this
continuous arc is made possible by the starting gases
and arc metals sealed inside the arc tube. The proper
start-up voltage also is needed to establish the arc.
Lamp start-up is not the same for all HID lamps.
Arc Tube Seal
Main Electrode
Starting Electrode
Arc Tube
Main Electrode
Glass Bulb
Arc Tube Seal
Arc Tube
Main Electrode
Glass Bulb
FIGURE 3. Components of HID lamp designs.
Mercury Vapor and Metal Halide
Lamp Starting
As just mentioned, both mercury vapor and halide
lamps use a separate starting electrode. This starting
electrode is located next to one of the main electrodes
inside the arc tube. The start-up electrode allows these
lamps to be started using a much lower start-up voltage
than required by HPS lamps.
When a mercury vapor or metal halide lamp is
energized, an electrical field is generated between one
of the main electrodes and the starting electrode next
to it. This causes an emission of electrons that ionize
the argon starting gas. The ionized argon particles
create a diffused argon arc between the two main
electrodes of the lamp (Figure 4).
The heat from this argon arc gradually vaporizes the
arc metals in the arc tube. These ionized arc metal
particles join the arc stream between the two main
electrodes. When a sufficient number of ionized
particles join the arc stream, the resistance between
the main electrodes drops to a point where the start-up
voltage supplied by the ballast can strike a current arc
across the main electrodes. The arc current continues
to increase until the current rating of the lamp is
reached; a process that normally takes several minutes.
The HID arc consists of a very rapid flow of both
electrons and charged arc metal ions. During this rapid
movement, countless collisions occur between ions and
electrons. As these particles collide, they release energy
at a specific wavelength (Figure 5). This energy appears
to us as light. Because the number of particles in the
arc tube is so great and the occurrence of collisions so
frequent, it appears that the entire arc path constantly
generates light.
The color of the light is a characteristic of the light
spectrum wavelength of the arc metals contained in
the arc tube. For example, in a mercury vapor lamp,
the mercury produces a distinct greenish white-blue
light. Red, orange and yellow hues appear grayish.
Main Electrode
Argon Gas
Visible and
Arc Tube
Electrical Field
Starting Electrode
Main Electrode
Main Electrode
Starting Electrode
Starting Resistor
Starting Resistor
Voltage to Lamp
FIGURE 4. Mercury vapor or metal halide lamp
Voltage to Lamp
FIGURE 5. Light production in an HID lamp.
Line Voltage
Metal End Cap
Arc Tube
FIGURE 6. Components of HID lamp designs.
In a metal halide lamp, the arc discharges through the
combined vapors of mercury and certain compounds
of iodine. The halide compounds help strengthen
yellows, greens and blues, so the overall color rendering
of metal halide lamps is green-white. Reds and oranges
appear dulled. Phosphor coatings on the bulbs of
mercury vapor and metal halide lamps can improve
color rendering and provide light diffusion.
Once a mercury vapor or metal halide lamp starts,
voltage drops to lower operating voltage levels. A resistor
or thermal switch in series with the starting electrode
now blocks voltage to the starting electrode so it does
not arc and burn out during normal lamp operation.
The arc tube of an HPS lamp is too narrow to house a
separate starting electrode. Since there is no starting
electrode in an HPS lamp, a much higher start-up
voltage is required to establish an arc between the wide
gaps of the main electrodes. This low-power, highvoltage spike ranges between 2500 and 4000 volts.
This voltage spike or pulse is provided by a starter pulse
circuit board separate from the ballast (Figure 6).
Note: Some lower wattage metal halide lamps (70-,
100- and 150-watt) also have arc tubes that are too
narrow to house separate starting electrodes. These
metal halide lamps now use an external starter board
such as those used in HPS lamps.
When an HPS lamp is energized, the high-voltage pulse
ionizes the xenon gas in the arc tube, and an arc is
established between the main electrodes. As soon as
this arc is established, the voltage pulse is switched
off. Sodium and mercury arc metals quickly vaporize
and join this arc stream, and the arc current increases
and stabilizes.
HPS lamps generate a sodium-based light that is
strongest in the yellow and orange range of the
spectrum and weakest in the blue-green wavelengths.
A small amount of mercury is added to the arc tube to
help strengthen blues and greens, but the overall color
rendering is still golden white, with both reds and blues
appearing grayed.
All three types of HID lamps require the use of a ballast
to assist in starting and limiting the current across the
arc once the arc has been struck. Remember that HID
lamps are negative resistance lamps. If a ballast were
not used, the arc discharge would draw an unlimited
amount of current and the lamp quickly would be
destroyed. More complete ballast information can be
found later in this manual.
Arc Tube Design
The arc tube of mercury vapor and metal halide lamps
is shorter and wider in diameter than an HPS arc tube.
This allows room for the starting electrode. Mercury
vapor and metal halide arc tubes are thin-walled tubes
made of high-quality quartz. The ends of the tube are
sealed by flame forming. This one-piece, press-fit
construction assures greater uniformity between lamps
and also holds and protects the thin leads of the
electrodes. As the two ends of the arc tube are heated
and pressed together, the two main electrodes and
thinner, starting electrode are imbedded in the molten
glass. The arc metal and starting gas are fed into the
tube through a glass straw welded into the arc tube. As
the glass straw is heated to the melting point, the
opening seals, trapping the gas and arc metal inside.
Both mercury vapor and metal halide arc tubes are
filled with the exact amount of arc metal (commonly
called amalgam) needed for operation. After an initial
100-hour burn-in time by the end user, mercury vapor
and metal halide lamps reach a stabilized operating
point at which all arc metal inside the tube is ionized
during start-up and operation. At this point, lamp voltage
becomes relatively constant throughout the rest of the
lamp’s operating life. There is a very slight voltage rise,
but it is not great enough to affect the life span of the
lamp. The same is not true of HPS lamps.
The arc tube of an HPS lamp is a slender cylinder
approximately 1/4” to 3/8” in diameter. Sodium cannot
be contained in a glass tube. The sodium would etch
the glass and further degrade light output. Sodium must
be contained in a metal container. Most lamp
manufacturers use a special ceramic material known
as polycrystalline alumina (PCA) to construct the HPS
arc tube. PCA is basically an aluminum oxide material
virtually insensitive to sodium attack.
PCA tube materials do not lend themselves to the
molten sealing method used in the construction of
mercury vapor and metal halide arc tubes. Instead, PCA
end caps, using either a wire-out end seal or a
compound (shrink-fit and cemented) end seal, are
epoxied or glued to the tube body using silicone glass.
Each tube end cap contains an electrode. The sodiummercury amalgam and starting gases are placed inside
the arc tube before it is sealed closed.
Unlike mercury vapor and metal halide lamps, HPS
lamps are excess amalgam lamps. This means there
is more sodium and mercury arc metal placed inside
the tube than can be vaporized during start-up and
operation. The amount of amalgam that vaporizes
depends on the total energy in the arc and the
temperature of the amalgam. If the lamp becomes too
hot, too much amalgam will vaporize, and operating
voltage will increase.
When HPS lamps were first introduced, the amalgam
not held in a vaporized state remained condensed in
an external reservoir located in the coolest part of the
lamp. If the lamp was vibrated by winds or passing
traffic, amalgam from the reservoir would splash down
onto the arc tube, causing a thermal shock that would
extinguish the lamp. The lamp would then go through
its start-up process and cycling would occur. Because
of this thermal blink-out problem all but one of the major
HPS lamp manufacturers have abandoned the external
amalgam reservoir design in favor of internal reservoirs
that do not create a thermal blink-out condition.
Experience has shown that during the first 20 minutes
or so of HPS lamp operation, the lamp voltage may
rise or fall from start to start, or even during continuous
operation, as varying amounts of amalgam enter the
arc stream.
Most HID lamps use a wire support frame to protect,
cushion, and align the arc tube in the center of the bulb.
The design and placement of this support frame is
particularly important in HPS lamps, because it can
affect the temperature of the arc tube and end caps.
As we have seen, arc tube temperature has a direct
effect on the amount of amalgam vaporized.
The construction and composition of the HPS main
electrodes also are very critical. Material discharged
from the electrodes during start-up and operation
redeposits on the arc tube ends in much the same way
the tungsten filament of an incandescent lamp
evaporates and blackens the bulb. This blackening of
the arc tube also will increase operating temperatures
and voltage across the arc tube.
HPS End-of-Life Voltage
With a number of factors contributing to HPS lamp
voltage rise, the increase in operating voltage over the
life of the lamp becomes significant. The operating
voltage of HPS lamps increases about 1-2 volts per
1000 hours operated. The life of an HPS lamp is
dependent on the rate of lamp voltage rise. Lamp
voltage will rise until it reaches the limit of the ballast
voltage available. At this point, the HPS lamp will cycle
ON and OFF, and its effective life will be over.
Certain operational characteristics are common to all
HID lamps. With any HID lamp, sufficient starting
current must be supplied to the lamp during the first
half-minute or so of operation. Too little current results
in the lamp never warming up properly, while too much
current will reduce lamp life. Too little current can be
caused by an improperly installed lamp, a bad
connection or a bad capacitor, or use of the incorrect
ballast or capacitor.
Due to manufacturing tolerances, individual HID lamps
operate within a range of operating voltages. For
example, as shown in Table 1, a 150-watt HPS lamp
rated at 55 volts can have a lamp voltage range of 48
to 62 volts.
HID lamps will operate at their rated wattages only if
the lamp and line voltages are nominal. Variations in
lamp and line voltages can cause a lamp wattage
variation of up to 20%.
HID lamps should not be operated at higher-than-rated
wattages. This can be caused by using a capacitor with
a rating too high for the fixture, or by installing a lamp
with a lower wattage rating than the fixture. Although
light output may increase, the excess wattage
dramatically increases operating temperatures of
electrodes, arc tubes and bulb walls. The arc tube may
bulge and possibly shatter. Lumen maintenance and
lamp life also are significantly decreased.
HID lamps also are sensitive to voltage interruptions. If
the lamp circuit is turned OFF, a momentary power
outage occurs, or the lamp voltage drops below the level
needed to sustain the arc discharge, the ions in the arc
tube deionize and light output stops. The lamp will not
restart immediately. This is because the arc gases are
now under pressure and the lamp must cool sufficiently
to reduce the vapor pressure to a level where the arc
will restrike at the available voltage. The time required
to relight is strongly influenced by the design of the
luminaire, since this will determine to a large extent the
cooling rate of the lamp. In general, mercury vapor lamps
will relight in 8 to 10 minutes, metal halide lamps in 10 to
45 minutes, and HPS lamps in 1 minute or less.
Light output from all types of HID lamps gradually
declines over time. Lumen maintenance depends on a
number of light loss factors. These include any physical
changes in the lamp, such as electrode deterioration,
blackening of the arc tube or bulb, shifts in the chemical
balance of the arc metals, or changes in ballast
performance. Longer burning cycles result in better
lumen maintenance because there is less stress on
lamp components due to frequent starting. Other factors
affecting lumen depreciation are lamp watts and
current, and the current waveform that is a function of
the lamp and luminaire circuit. Ambient temperature
does not have a great effect on the maintained light
output of HID lamps.
Lamp Life1
16,000+ Hrs.
24,000+ Hrs.
24,000+ Hrs.
24,000+ Hrs.
24,000+ Hrs.
(55 volts)
24,000+ Hrs.
(100 volts)
24,000+ Hrs.
24,000+ Hrs.
24,000+ Hrs.
24,000+ Hrs.
1000 24,000+ Hrs.
Voltage Voltage3
NEW Lamp
Voltage Range
(at 100 Hours)2
End-of-Life Volts Increase
Per 1,000
Hours Life
Rated lamp life is based on 50% survival.
100 hours is lamp manufacturer specification for stabilizing light output.
Also called open circuit.
CAUTION: Disconnect starting lead not common to the lamp to eliminate the starting voltage when checking
the minimum open circuit voltage. The starting voltage may damage your voltmeter.
HPS Lamps
HPS lamps have excellent lumen maintenance (Figure
7A). HPS lamps still are generating 90% of initial light
output at the midpoint of their life span. Lumen
maintenance at the end of life still is excellent at
around 80%.
Mercury Vapor Lamps
The graph in Figure 7B covers the lumen depreciation
curves for a range of mercury vapor lamp wattages.
Maintenance of most types falls in the darkly shaded
area. Frequent starting or lamp burning position has
very little effect on mercury vapor lumen maintenance.
The rated average life of HID lamps is the life obtained
from a large group of test lamps burned under
controlled conditions at 10 or more burning hours per
start. It is based on the survival of at least 50% of the
lamps or groups of lamps and can vary considerably
from the average. Factors affecting HID lamp life
include: lamp operating wattage, lamp operating
temperature, ballast characteristics, line voltage and
burning hours per start. Lamp age, or the number of
hours a lamp has operated, has very little effect on
lamp startability, although metal halide lamps can
require longer starting times as they age.
Metal Halide Lamps
HPS Lamps
As the graph in Figure 7C shows, the light output of
metal halide lamps declines more rapidly than either
HPS or mercury vapor lamps. Frequent starting will
shorten metal halide lamp life.
Initial Lumens (Percent)
Initial Lumens (Percent)
Initial Lumens (Percent)
Approximate Lumen Maintenance
of Metal Halide Lamps
Approximate Lumen Maintenance
of Mercury Vapor Lamps
Approximate Lumen Maintenance
of HPS Lamps
As shown in the lamp survival curve in Figure 8A, HPS
lamps have a long average life span of 24,000 plus
hours. Normal end of life occurs when the lamp begins
to cycle on and off due to excessive lamp voltage rise.
Rated Average Life (Percent)
Hours Burned (Thousands)
Hours Burned (Thousands)
FIGURE 7. HID lamp lumens maintenance curves: (A) HPS, (B) mercury vapor, (C) metal halide.
Approximate Survival Curve
of Metal Halide Lamps
Approximate Survival Curve
of Mercury Vapor Lamps
Approximate Survival Curve
of HPS Lamps
Survival (Percent)
Initial Lumens (Percent)
Initial Lumens (Percent)
Hours Burned (Thousands)
Hours Burned (Thousands)
Rated Average Life (Percent)
FIGURE 8. HID lamp life curves: (A) HPS, (B) mercury vapor, (C) metal halide.
More frequent starts will cause voltage to rise faster,
as will overwattage operation. Slight underwattage
operation will have no adverse effect on lamp life.
Mercury Vapor Lamps
Mercury vapor lamps have an extremely long-rated life,
exceeding 24,000 hours (Figure 8B). Mercury lamps
should be replaced before they burn out due to
decreases in lumen output. Frequent starting does not
adversely affect lamp life as significantly as other HID
lamps. The normal mode of failure is the inability to start.
Metal Halide Lamps
Metal halide lamps have an average-rated life span of
3,000 to 20,000 hours, depending on lamp wattage.
Lamp life generally is much shorter than HPS and
mercury vapor due to poorer lumen maintenance and
the presence of iodine compounds in the arc tube. The
normal failure mode is the inability to start because of
increased starting voltage requirements. Frequent
starting also will adversely affect lamp life, as will
overwattage operation.
Troubleshooting and repairing HPS lighting fixtures
involve working with some components and operating
principles not found in mercury vapor or metal halide
fixtures. Now that you understand the primary differences
between HPS, mercury vapor, and metal halide
operation, it’s time to discuss how these differences
affect troubleshooting and repairing procedures.
The starter is used only during the first few moments
of lamp start-up. Once the starting gas arc is struck
between the main electrodes, the starter turns OFF and
does not operate until it is needed again. Many service
technicians unfamiliar with HPS starter operations are
unaware of this fact. They automatically replace the
starter when faced with an HPS lamp that cycles ON
and OFF, particularly if the cycling is intermittent. The
technician assumes the starter is at fault. In fact, it is
operating repeatedly—it is turning the lamp ON not
once, but many times.
The external starter must be properly matched to the
lamp, luminaire and ballast. There are slight design and
operating differences between starter manufacturers,
and mixing starters could result in unreliable starts.
There also are differences in the various wattage
match-ups provided by the fixture manufacturers.
Therefore, mixing various wattage ballasts with various
starting circuits is not recommended as this also could
result in unreliable starting.
Starter Operation
An HPS starter operates similarly to an automotive
breaker point ignition system. The ignition system is
made of two interconnected circuits: the primary (lowvoltage) circuit and the secondary (high-voltage) circuit.
When the ignition switch is turned ON, current flows to
the ignition coil’s primary winding, through the breaker
points, to ground. This low-voltage current flow in the
coil’s primary winding creates a magnetic field. When
the current flow is interrupted as the breaker points
open, the magnetic field collapses, and a high-voltage
surge is induced in the coil’s secondary winding.
HPS Lamp Starters
Inspection of an HPS luminaire will reveal an additional
component not found in mercury vapor or metal halide
fixtures—an external starter (Figure 9). This starter
can be found as a printed electronic circuit board in
some luminaires. The starter also may be packaged
in a small plastic cube or can. Regardless of how they
are packaged, external starters all perform the same
function: they increase the 120 or 240 volts supplied
to the lamp to the 2500 to 4000 volts needed to start
the lamp.
Note: 1000-watt HPS lamps require a minimum
starting voltage of 3000 volts and a maximum of
5000 volts. As explained earlier, this high-voltage
spike is needed to bridge the wide gap between
the HPS lamp’s main electrodes.
FIGURE 9. Starter circuit in typical HPS circuit.
The high-voltage surge from the secondary coil windings
flows to the distributor via an ignition cable. From the
distributor, high voltage is delivered through cables to
the individual spark plugs, where it arcs across the plug
electrodes to ignite the air/fuel mixture in the cylinder.
Opening and closing the points acts as a switch. Timing
of the open/close switching is controlled by a camshaft
in the distributor. As the camshaft turns, lobes on the
shaft open and close the points. A condenser, which is
actually a capacitor, promotes fast and complete
breakdown of the magnetic field in the primary coil.
This helps produce a strong induced voltage in the
secondary coil.
An HPS lamp starter contains corresponding
components. An electronic switch acts in place of the
mechanical breaker points of the ignition system. The
starter circuit contains a capacitor that corresponds to
the ignition system condenser. The HPS ballast acts
as the ignition system’s primary and secondary coils.
The electrodes in the arc tube correspond to the spark
plug electrodes, and the starting gas acts as the
combustible fuel.
The electronic switch of the starter is activated by the
rise and fall of the voltage levels that occur in the 60cycle alternating current (AC) used to power the lighting
fixture. As you can see from the 120-volt AC waveform
shown in Figure 10, the voltage cycles from 0 to 177
volts, to 0 to 177 volts again, 60 times per second. The
average voltage is 120 volts. As the voltage rises and
falls in each half cycle, the electronic switch opens and
closes, just as the breaker points in the automotive
distributor open and close when the distributor camshaft
is rotated.
Switch Closes
The capacitor also plays an important role in the
operation of the starter. When the light fixture is turned
ON, the capacitor is charged by the rise in voltage in
the 60 cycle AC. When the voltage rises to the upper
portion of the generated half cycle, the voltage level
reaches a point that causes the electronic switch to
close. Once the electronic switch closes, the charged
capacitor is given a discharge path to the 10 to 12
winding turns of the tapped portion of the ballast (Figure
11). The ballast tap acts as a primary coil.
The high-voltage step-up in the ballast is accomplished
in much the same way as in the automotive ignition
coil previously described. Current from the charged
capacitor passes through the 10 to 12 windings of the
ballast tap, creating a magnetic field. When the starter’s
electronic switch opens, the capacitor’s path to the
ballast tap is momentarily broken and the magnetic field
collapses inward toward the center of the ballast output
coil. The magnetic lines of force that were created in
the tap windings cut across the hundreds of turns of
fine wire that make up the output coil. As a result, the
electron balance in the output coil wire is upset and
voltage is produced in the output coil windings.
The current flow from the output windings has high
voltage because the output coil is made of hundreds of
wire turns. As the magnetic field falls inward, it cuts
across each turn of wire, generating a certain amount
of voltage in each loop. Since the loops are connected
in series, the voltage produced in one loop is added to
the voltage produced in the succeeding loops. By the
time the lines of force have fallen all the way to the
center of the output coil, the necessary 2500- to 4000volt starting pulse has been generated.
Max Voltage177 V
177 V
Switch Opens
(Approximately 100V)
Max Voltage
177 V
Switch Closes
177 V
Switch Opens
Time 1/60 Second
FIGURE 10. The electronic switch in the starter circuit
closes every time voltage of 60 cycle AC power source
rises above a certain level.
FIGURE 11. Ballast tap acts as a primary coil.
In effect, the ballast acts like a step-up transformer.
For example, consider a ballast with 10 turns of wire
in its tap coil and 300 turns of wire in its output coil. If
the HPS starter capacitor charges to 100 volts and
then discharges through the switch into the 10 turns
of the ballast tap, the 100 volts would be divided over
the 10 turns, and each turn would have 10 volts on it.
When the magnetic field collapses, the 10 volts per
tap turn would then be magnetically transferred to
induce 10 volts on each of the 300 turns of the output
coil. This would result in a total voltage output of 3000
volts (10 volts x 300 turns = 3000 volts). This example
is a vast oversimplification. In actual transformer
design, other considerations must be accounted for,
such as wire and core losses. But the general operating
principle is correct.
The HPS luminaire ballast also performs a number of
other functions necessary in starting and operating the
lamp. For example, the ballast allows a lower voltage to
be placed on the arc tube electrodes during start-up and
operation of the lamp. This lower voltage is the source
of voltage needed to both start the lamp and then
maintain and help in controlling the operation of the lamp.
For example, HPS lamps in the 35- to 150-watt range
have an initial open circuit voltage of 110 to 120 volts.
When the lamp starts, it pulls the ballast’s secondary
voltage down to approximately 15 volts. As the lamp
warms up over the next several minutes, the lamp
voltage rises to its rated operating level, which is usually
between 44 and 62 volts. Operating voltage stabilizes
at this time and the lamp operates at its rated light output
and color rendering capabilities. See Table 1 for a
complete summary of typical HPS lamp data.
The lower 44- to 62-volt operating voltage also keeps
the HPS starter turned OFF. Remember, the electronic
switch in the starter will close only when voltages in the
neighborhood of 100 volts are applied to it. Once the
lamp starts and the ballast decreases voltage to the
44- to 62-volt range, the electronic switch remains open
and the charging and discharging of the capacitor
cannot take place. The 2500- to 4000-volt starting pulse
can no longer be produced until the lamp is turned OFF
and the initial open circuit voltage of 110 to 120 volts is
applied to the starter circuit.
Starter Variations
Since the commercial introduction of HPS lamps in the
mid-1960s, very few changes have taken place in the
starting principles of the lamp. Early starters used a
transistor-type electronic switch that required additional
electronic components to achieve the proper timing of
the switching operation. Modern starter designs use a
self-timing device that minimizes the number of
electronic components. Fewer components have made
modern starters more reliable.
Instant Restrike Starters
A standard HPS lamp starter requires that the lamp
cool down for approximately one (1) minute before it
can be restarted. Instant restrike devices that generate
two to four times the normal maximum pulse voltage
are available. This voltage is strong enough to
overcome the gas pressure inside the arc tube and
instantly reionize the gases, restarting the lamp. Instant
restart devices usually are required in industrial
applications where safety rules require the restoration
of light within a short period of time after a power outage
has occurred. Instant restrike starters are more
expensive than standard starters.
Two-Lead Starters
One recent innovation in HPS starter technology is the
two-lead starter (Figure 12). This HPS lamp starter
contains its own ignition coil and does not rely on the
ballast to provide voltage step-up. Some two-lead
starters can be used with any manufacturer’s ballasts.
In contrast, starters that use the ballast as an ignition
coil are not readily interchangeable. The reason for this
is that the turns ratio between the ballast tap and the
output coil portion of the ballast varies from one
manufacturer to another. This, coupled with differences
in electronic component values between
manufacturers, can lead to mismatch problems. A new
lamp usually will start with a mismatched starter and
ballast, but significantly reduced lamp life or premature
ballast failure is likely.
Limited lamp life can occur when the mismatch does
not allow the proper starting pulse to be produced. If
the starting voltage pulse exceeds the lamp
manufacturer’s limits, the arc tube electrodes will erode
away, causing premature lamp cycling or an outage.
Excessive starting voltages also can short out the
ballast, resulting in ballast burnout, or can break down
the lamp socket or the lamp base internally. If the
starting pulse is too low, then lamp starting will become
unreliable early in lamp life.
The two-lead starter eliminates mismatching problems
when used with various manufacturers’ ballasts. The
two-lead starter operates on the lamp socket voltage,
which is an ANSI standard.
480 V
X3 tap
480 V
Remove Tap Connection or Insulate
FIGURE 12. Two-lead starters have their own ignition coil.
It produces its own step-up voltage pulse and sends it
to the lamp. When the two-lead starter is installed, the
lead on the ballast that runs from the ballast tap to the
starter is disconnected. This disables the starting
function of the ballast, now handled by the two-lead
starter. However, the ballast still can perform its other
current and voltage regulation functions.
Two-lead starters are ideal for users that must maintain
a wide range of luminaires built by different
manufacturers. They also solve the problem of
obtaining properly matched replacement parts.
As we have discussed, the ballast performs a number of
important functions in HID lamp operation. These include:
1. Providing the correct starting current.
2. Providing the correct starting voltage.
3. Limiting current to the lamp. The most basic
function performed by a ballast is to limit the flow
of current through the lamp. When the lamp starts
and begins operation, it basically is operating as a
short circuit across the electrodes. The ballast
connected with the lamp acts to limit the current
flowing to the lamp to keep it from destroying itself
as resistance develops. Without the limiting
capability of the ballast, the lamp would draw more
and more current and eventually explode.
4. Providing the correct voltage to stabilize lamp
operation. We also have discussed how a ballast
can act as a transformer to step-up line voltage
levels needed to start the lamp. Many mercury
vapor and metal halide lamps are designed to start
using approximately 240 volts. If this voltage is not
available, transformers are used inside the ballast
to change the available voltage into the 240 volts
needed for start-up. For example, if 120 volts is
applied to a 100-turn primary coil, a secondary
output coil with 200 turns will produce the needed
240 volts for start-up.
By altering the ratio between the number of primary
and secondary coil turns, and including the
necessary switching circuitry, the ballast also can
produce the 2500- to 4000-volt low energy voltage
spike needed to start HPS lamps.
5. Regulating the flow of current through the arc
discharge. As mentioned in our discussion of lamp
operation, HID lamps reach a point of equilibrium
several minutes after start-up. Changes that affect
the temperature of the arc tube, such as changes
in the voltage supplied to the lamp through the
ballast, can produce significant variations in the
lamp’s wattage and light output. Ballasts act to
reduce this variation by absorbing part of this
varying voltage input.
By subjecting the steel core of the ballast to high
amounts of magnetic force, you also can change
the ratio at which voltage is transferred between its
primary and secondary coils. For example, a ballast
can be designed to have a given voltage transfer
ratio at a predetermined input voltage. However, if
input voltage begins to increase from this value, the
steel core of the ballast becomes overworked or
saturated by magnetic force. The result is that
increases in voltage in the primary coil are not
transferred to the secondary coil, nor are they passed
on to the lamp. Instead, the ballast continues to
output voltage at the proper levels. This is the basic
design principle used in all regulated ballasts. The
secondary or lamp is isolated from changes in the
primary or power supply.
6. Compensating for the low power factor
characteristic of the arc discharge. Ballasts are
classified as either normal or high power factor. A
normal power factor ballast and HID lamp
combination has a power factor of approximately
50%. This means that for a given wattage more
than twice as much current is required to operate
the HID lamp and ballast as would be needed to
operate an ordinary incandescent lamp with the
same wattage rating. Normal power factor ballasts
are commonly used in reactor and high-reactancetype ballast circuits for both mercury vapor and HPS
lamps. They commonly are used for lower wattage
lamps of 150 watts or less.
A high power factor ballast is one that draws within
10% of the minimum line voltage for a specific
power consumption. This type of ballast is
described as having a power factor of 90% or
greater. High power factor ballasts allow the use
of a large number of luminaires and high wattage
lamps on each branch circuit.
The total power in any direct current (DC) circuit or
in any AC circuit with only resistance loads, such
as incandescent filament lamps, is expressed by
the fundamental equation:
Total Watts = Volts x Amperes
In such circuits, the total watts are active in doing
useful work, such as producing light. In an HID lamp
circuit that requires a ballast, some of the current
is not effective in operating the ballast or in
producing light. So in an HID circuit, the product of
volts and amperes does not equal the active watts
as read by a wattmeter because such a meter
measures only the active power used. It is,
therefore, necessary to express the active watts in
an HID lamp circuit as follows:
Watts = Volts x Amperes x Power Factor
Amperes =
Total Watts (Active)
Volts x Power Factor
The power factor is the ratio of the active power as
read on the wattmeter to the product of the volts
and amperes as read on meters placed in the HID
circuit. This ratio usually is expressed as a
Power Factor =
Total Watts (Active)
Amperes x Volts
Using the equation Total Watts = Volts x Amperes
x Power Factor, it is easy to see how the power
factor of a ballast affects the total current in a circuit.
When the power factor is 100%, the current is at a
minimum and the product of the amperes and volts
is equal to the active watts as measured by a
wattmeter. However, if the ballast has a power factor
of 50%, the current in the circuit is doubled. If the
ballast power factor is 90%, the current will be
increased by only 10%. Failure to consider the effect
of power factor on the current, especially when the
circuits are heavily loaded, can result in overheated
wires, excessive voltage drop, or interruptions
caused by the operation of protective equipment.
Ballast Type
Typical Line Voltage
% Lamp Wattage Change
% Input Voltage Change
Power Factor (P.F.)
Mercury Vapor
Metal Additive
Metal Additive (for approved mercury ballast)
HPS (no starting circuit, mercury ballasted)
Low-Pressure Sodium
Auto Auto (CWA)
Wattage (CW) Voltage
NOTE: X indicates equipment that is normally appropriate for a given source.
* Capacitor required for high power factor only.
** All voltages.
*** Specially designed CWA-type ballast for metal additive lamps.
Ballast Characteristics
Typical characteristics of ballasts used in HID lighting
systems are summarized in Table 2. Figure 13
illustrates luminaire wiring diagrams for the various
ballasts used in HID lighting systems. Other
characteristics are as follows:
Ballast Efficiency: No ballast delivers all of the current
passing through it to the lamp it serves. Some power
always is lost in the form of resistance heat. A ballast
that is 90% efficient delivers 90% of the power to the
lamp. The remaining 10% is wasted in heating the ballast.
The ballast watt losses add to the total power consumed.
Line Voltage: For some ballasts, the line voltage as
the lamp starts is less than the final operating voltage.
In these cases, fuses and circuit breaker ratings should
be based on the operating voltage value. For other
ballasts, the starting voltage is considerably higher than
the final operating voltage, so circuit protection must
be sized to accommodate starting voltage levels.
Line Voltage Regulation: Variations in line voltage can
be caused by system demands and other factors.
Newer power systems normally operate within +5% of
the rated system voltage, but in some older systems
the daily voltage variation can be as high as 10%. The
ballast selected must be able to accommodate these
voltage fluctuations.
Extinction Voltage: All power systems are subject to
dips in line voltage that normally are around 10%, but
occasionally can reach 20% to 30%. The ballast
should be capable of riding out these dips without
extinguishing the lamp.
Reactor Ballasts
Reactors are the simplest type of ballast. They consist
of a single coil or wire on a core of steel. Functionally,
they act as current limiters and provide some lamp
wattage regulation. Reactors are normal power factor
ballasts, but a capacitor can be added to provide high
power factor performance. The units are designed for
+5% input voltage variation and limit or regulate lamp
wattage to a +12% variation within that range. For
example, in a 240-volt, 400-watt reactor ballast, voltage
can vary from 228 to 252 volts (+5%) and wattage from
352 to 448 watts (+ 12%). Characteristically, reactor
ballasts require a higher start-up current than operating
current. They only are used when the available line
voltage is at least two times greater than the lamp-rated
operating voltage.
An HPS reactor ballast contains a starting circuit that
provides the proper pulse voltage for starting the lamp.
Lag Auto Ballasts
This type of ballast is known by several names: lag auto,
lag or high reactance ballast. It is used when the line
voltage is 120 volts and socket voltage is in the 240volt range. This ballast consists of two coils on a core
of steel. Together, the tap and output coils transform
the line voltage into the required starting voltage.
FIGURE 13. Circuit diagrams for various types of ballasts used in HID applications.
The ballast also limits lamp current. Lag auto ballasts
have the same operating and performance
characteristics as reactor ballasts. This type of ballast
normally is used with mercury vapor and HPS lamps.
sudden dips in line voltage without lamp shutdown. This
type of ballast is most commonly used in area, sports
and indoor HID lighting.
Constant Wattage Ballasts
Constant Wattage
Autotransformer Ballasts
These ballasts also are called regulated or
autoregulator ballasts. The constant wattage
autotransformer (CWA) ballast consists of two coils on
a core of steel and a capacitor in series with the lamp.
CWA ballasts perform the basic jobs of current limiting
and voltage transformation. In addition, CWA ballasts
are always high power factor ballasts. They have
starting currents that are less than the operating current.
In regard to voltage regulation, CWA ballasts offer
significant improvements over reactor and lag auto
designs. CWA ballasts are designed to handle a +10%
line voltage variation. Over this range, they will maintain
lamp wattage within +5%, a four-fold improvement over
reactor and lag auto ballasts. They also can handle
Also called isolated regulated-premium constant
wattage ballasts, this ballast design limits current,
performs voltage transformation and provides the best
lamp wattage regulation available. They are designed
to operate over a voltage range of +13%, maintaining
lamp wattage to within +2.5%. Constant wattage (CW)
ballasts have a high power factor and a lower starting
current than operating current. These ballasts are
similar in construction to CWA ballasts.
HPS Mag Reg
Also called reg lag, mag reg ballasts are used to meet
HPS lamp wattage requirements on systems having a
+10% voltage variation. These are high power factor
ballasts that have lower starting than operating current
requirements. The mag reg transformer consists of
three isolated coils on a core of steel.
Matching Lamp and Ballasts
To Power Line
It is very important to match lamp and ballast to attain
proper lumen output and lamp life. HPS lamps rated at
55 volts can use a single coil reactor-type ballast having
a separate starting circuit. A secondary coil is not
needed in this case for voltage step-up, and the singlecoil ballast generates less heat.
When installing replacement lamps, be sure the lamp
voltage and wattage rating match the ratings of the
fixture and ballast. For example, installing a 150-watt,
55-volt HPS light bulb in a fixture equipped with a 150watt, 100-volt ballast will result in a dim burner. This is
because the given ballast limits current to the lamp to
1.8 amperes. A 150-watt, 55-volt HPS lamp requires
3.2 amperes of current to reach full brightness. Ballast
and lamp wattages must also match. Installing a 250watt lamp in a 175-watt ballast fixture will result in a
dim burning lamp. On the other hand, installing a 175watt lamp in a 250-watt fixture will drastically reduce
lamp life. A dim burner also can be caused by a shorted
or incorrect capacitor.
HID fixtures used in outdoor lighting applications such
as roadway, area, site and security lighting can be
equipped with photocontrol units that automatically turn
the fixture on at dusk and off at dawn (Figure 14).
FIGURE 14. Typical photocontrol for HID luminaire.
The photocontrol, or photocell as it is sometimes called,
consists of a small cadmium-sulfide cell wired in series
with an electrical relay (Figure 15). Keep in mind that
the cadmium-sulfide cell is not an energy-producing
cell. It does not convert the sun’s energy into a voltage.
Armature and Contacts
To Line Neutral
FIGURE 15. Photocontrol components and circuit.
The cell is a variable resistor, similar to those used to
turn the volume of a radio up or down. The amount of
light that strikes the cell increases or decreases the
amount of electrical resistance in the cell.
During the day, when light strikes the photocell,
resistance in the cell is very low. Current from the
service drop can flow through the cell to the coil of the
photocontrol relay. When the coil is energized, it creates
a magnetic field that pulls in the armature of the relay.
This armature movement opens the contacts to the
fixture ballast. The lamp cannot operate with no line
voltage supplied to the ballast.
As darkness falls, less and less light strikes the
photocell and electrical resistance in the cell begins to
increase. Less and less current passes through the
relay coil and strength of the magnetic field generated
by the coil drops. Finally, the magnetic field becomes
so weak that it cannot hold in the armature, and the
armature moves over to its open position. When the
relay armature is in its open position, it closes the
contacts to the ballast. Line voltage is applied to the
ballast, and the lamp begins its start-up sequence. The
lamp will operate until the light of sunrise again
decreases resistance in the cell. This initiates current
flow to the relay coil. The coil energizes and its magnetic
field pulls the relay armature closed. This cuts line
voltage to the ballast and the lamp turns OFF.
The photocontrol works because it uses a sensitive
relay that operates on a very slow-changing voltage.
The relay reacts to any voltage less than system
voltage. An operational photocontrol will emit a soft,
humming noise as it approaches its pull-in voltage. You
will hear a slight click as the relay contacts close.
A defective or damaged photocontrol will emit a growling
noise as it nears its pull-in voltage. This sound
resembles a door bell buzzer and usually is caused by
misaligned relay contacts. The photocontrol may
continue to growl and never completely close its
contacts. Or it may growl and then close its contacts.
In either case, never use a photocontrol that can be
made to growl or buzz during testing.
Test photocontrol operation by covering the photocell
with your hand to simulate darkness (Figure 16). It
should click open as you cover it and then click closed
when you remove your hand. Repeat this test several
times to center the relay armature. Now cover the cell
completely and then very slowly uncover it in small
stages to simulate sunrise. You should be able to trick
the cell into humming lightly as it approaches its pull-in
voltage. If you can trick the photocontrol into growling,
replace it, or if it is new, do not use it.
When installing a photocell into its receptacle, make
sure it is locked into position and does not pull out.
Make sure the receptacle mounting screws are fully
tightened and holding. Otherwise, the springy nature
of the gasket used to seal the photocell mounting
surface will push the photocell upward and it will not be
seated properly in its receptacle. Any vibration also will
help push an improperly mounted photocell off its
contacts. The contacts will then arc and burn, causing
heat damage as just described.
All HPS lamps experience voltage rise during their life
and have a designed end-of-life voltage rating. When
the voltage rise reaches the end-of-life voltage, the
ballast cannot supply the needed operating voltage, the
lamp goes out, and cycling begins. As the hot lamp
cools, it restarts at a lower than end-of-life voltage. But
as the lamp begins to heat up again, its operating
voltage soon rises past its end-of-life voltage. The lamp
turns OFF and the cycle repeats itself.
End-of-life cycling can occur in an HPS lamp at the
time of installation, at six years, at end of life or at any
time in between. A bad lamp can fail prematurely. In
most cases, cycling is caused by a voltage rise due to
increased lamp resistance, electrode wear, etc.
Equipment Mismatching
FIGURE 16. Testing photocontrol operation. By
gradually exposing the cell to light by moving your
hand, you can trick the relay into closing.
A luminaire burning night and day is the most common
indication of a failed photocontrol. A day burner is
caused by the armature contacts of the photocontrol
welding together due to an electrical heat buildup from
“chattering” relay contacts. Coil circuit failure also can
cause a day burner. Excessive heat also can pass from
the photocontrol line twist lock connector pin through
the photocontrol receptacle, weakening the
photocontrol twist lock receptacle contacts. This is a
common cause of early photocontrol failure. Heat also
can deform the contact mounting in the photocontrol
receptacle. Whenever you replace or inspect the
photocontrol, also inspect the receptacle for signs of
heat damage. Look for charred or deformed plastic or
other signs of damage. Replace the fixture if the
receptacle is damaged.
Using the wrong lamp in the fixture (Figure 17) can cause
cycling. As shown in Table 1, 150-watt HPS lamps are
manufactured in two voltage ratings: 55 volts and 100
volts. HPS 150-watt lamps will have their voltage rating
stamped on the lamp body to avoid confusion when
replacing these lamps. A 150-watt, 100-volt HPS lamp
installed in a 150-watt, 55-volt fixture will cause cycling
because the 55-volt ballast does not supply the
necessary voltage required by the 100-volt lamp.
Make sure lamp matches fixture
FIGURE 17. Checking the correct lamp.
Using a lower wattage HPS lamp in a higher wattage
fixture, such as a 70-watt lamp in a 150-watt fixture,
also may cause cycling.
Using the wrong or defective ballast or capacitor also
can lead to cycling. Also be sure the ballast and
capacitor are wired correctly.
Reignition Phenomenon
HPS and other HID lamps actually turn ON and OFF
120 times per second. Current is cut off for a millisecond
or so at each midpoint, or zero crossing point, of the
AC 60 Hertz cycle (Figure 18A). The lamp stays hot
enough to automatically restrike after this very, very
short outage. However, if several cycles of the AC power
are lost or drop out due to loose wire connections or
shorts, the lamp cools sufficiently to turn OFF and will
not restrike immediately (Figure 18B).
installed. If the center contact and lamp tip become
misaligned due to a mismatch between the socket
contact and the lamp tip, the lamp may not start due to
poor or partial contact between the two. If this problem
occurs, some service technicians may try turning the
lamp out 1/2 turn or so. In some cases, the lamp may
now light, but this is not an acceptable solution to the
problem. The connection between the lamp and socket
is not under full spring pressure, and electrical arcing
will occur, drastically reducing lamp life or resulting in
socket burnout.
Vibration Sensitivity
HPS lamps nearing the end of their service lives are
very vibration sensitive. Vibration causes a rise in lamp
current above the end-of-life voltage. HPS light color
gives a good indication of relative lamp age. Older HPS
lamps give off a whiter light. The color rendition they
produce actually is better than new HPS lamps.
To avoid dropouts due to poor connections, do not pull
the wires tight when installing the luminaire or its internal
components such as the ballast, photocontrol, starter
or capacitor. The lamp must be screwed into the socket
properly to make a good connection. The coil spring
must be compressed completely to make proper
contact at the base of the socket. All of the metal on
the lamp’s screw base should be hidden below the rim
of the socket when the lamp is screwed in completely.
Vibration in the lamp due to wind or traffic can cause
the lamp to cycle. Vibration-induced cycling is common
in fixtures mounted on bridges. You can simulate this
vibration in a burning lamp by striking the mounting
pole with a short length of lumber, or by actually
bumping the light fixture or light bulb with your hand. If
the lamp turns OFF when the pole is struck, it is
probably vibration sensitive.
The lamp socket center contact and the tip of the lamp
base must be in proper contact when the lamp is
The bump test also is a good way to check for intermittent
open circuits and poor connections in the lamp and fixture.
177 V
177 V
Several Cycles Are Lost.
Drop Out Occurs.
FIGURE 18. (A) Voltage actually is cut to the lamp every time alternating current changes direction.
This happens 120 times per second with 60 Hertz AC power.
(B) When several cycles of AC current drop out or are lost, the lamp will turn OFF.
For example, the lamp’s internal mounting frame is
designed to allow the arc tube to move as it expands
and contracts with changes in temperature. The metal
mounting frame is stable, but the arc tube connects to
the lamp base through the use of a flexible bond strap.
Over time, the bond strap weld can fail, causing
intermittent contact. A bump test often will detect this
type of failure.
Keep in mind that normal end-of-life cycling is marked
by a more or less predictable on/off pattern of a minute
or so ON and a minute or so OFF. Cycling caused by
open contacts or bad welds is much more
unpredictable. The lamp may stay ON or OFF for
several minutes or several hours.
When you field test a lamp with cycling problems,
remember to test the photocontrol operation. As the
lamp starts to come up, bump it to see if you can make
it cycle OFF. You may even be able to see the slight
electrical arcing at the bad connection. You also should
bump test the lamp after it has started and stabilized.
Thermal Cycling
Thermal cycling is another vibration- or movementinduced problem that occurs in HPS lamps. Thermal
blink-out is most common in exterior reservoir lamps
operated in a position that places the amalgam reservoir
above horizontal in the light fixture. However, severe
vibration problems can cause thermal cycling in all types
of HPS lamps. Vibration or movement due to wind,
traffic or other reasons can cause excess amalgam to
splash down onto the white-hot electrode, giving it a
thermal shock. This thermal shock causes the lamp to
drop out and cycle.
Bridge and viaduct installations are prone to thermal
cycling problems. Thermal cycling can be avoided by
selecting nonexternal reservoir-type lamps for highvibration applications. In severe vibration conditions,
thermal cycling could be fixture related. You can test
for thermal cycling using the bump test.
Photocontrol-Induced Cycling
An overly sensitive photocontrol unit may cause cycling
in an HPS or HID lamp installation. Light from the
luminaire, or from other light sources around it, can
trick the photocontrol causing it to turn OFF the
luminaire. Aim the photocontrol away from strong light
sources, or install shields to cut down on the level of
ambient light entering the photocell (Figure 19).
Seasonal changes can cause cycling problems due to
reflective light differences between green leaves in
spring and summer, and dead leaves and exposed tree
bark in fall and winter.
FIGURE 19. Shielding the photocontrol from high
ambient light levels.
When compared to mercury vapor and metal halide
lamps, HPS lamps produce up to twice the amount of
light per watt of power consumed. In terms of lumen
maintenance, they outperform the other HID lamps by
as much as three to one, and HPS lamp life is
comparable to mercury vapor as the longest available
in HID lighting. This all adds up to an extremely good
lighting value. But HPS lighting offers another great
value that often is overlooked—the ability to pretest and
predetermine HPS lamp and luminaire performance
before field installation.
Experience has shown that a short, easy-to-perform
lamp voltage test can help eliminate potential earlyfailure HPS lamps and also can detect luminaires that
could overdrive lamps and cause new good lamps to
fail early in their rated life.
Spot (individual) lamp replacement is costly, and any
unusually high failure rate due to defective equipment or
components can be expensive, particularly when the
replacements are being drawn from the same stock of
lamps or luminaires that are failing in the first place. The
time it takes to sample test 100 luminaires and lamps
usually will be less than the time it would take a service
technician to drive to a defective luminaire or outage, set
up the bucket truck, change the lamp and/or luminaire,
and drive to the next defective luminaire/lamp location.
Test Procedures
An HPS lamp can be pretested due to its voltage rise
during its lifetime. For example, a new 100-watt HPS
lamp is nominally rated at 55 volts, with an operating
voltage range of 45 to 62 volts. This operating voltage
usually stabilizes within 10 to 15 minutes after startup. The 100-watt HPS lamp has an end-of-life voltage
of 84 volts.
The projected life of the 100-watt HPS lamp is based
on a lamp voltage rise from the 45- to 62-volt range to
the 84-volt end-of-life voltage. This slow voltage rise
usually takes about six years of normal operation.
However, if a new HPS lamp tests higher than this 45to 62-volt operating range, in the neighborhood of 70
volts for example, experience has shown that the rate
of voltage increase will be significantly higher. The lamp
will have a dramatically reduced life, and is a likely
candidate for spot replacement if installed in the field.
Note: The above voltages are based on an ANSI
standard where a nominal ballast is used on its
nominal design voltage. Experience has shown that
a slight 2- or 3-volt variation out of this range has
not been detrimental to lamp life. For example, a
lamp rated at 45 to 62 volts will operate
satisfactorily in the 42- to 65-volt range.
Selecting the Test Group
In most cases, testing of 5% to 7% of the lamp or
luminaire inventory is sufficient when testing for possible
defective lamp or luminaire batches or runs. However,
100% pretesting may be more economical if the lamps
and luminaires are to be installed in a high-cost
maintenance location, such as a high-traffic roadway
near a major airport. Spot lamp replacement in these
areas can cost several hundred dollars for a single lamp.
If a 5% to 7% sampling is being used, be sure to select
the lamps and luminaires from different batches or runs
in your equipment inventory. Check the run or batch
number that appears on the lamp or luminaire carton.
This usually is either a code number or an actual run
date indicating the day and time the unit was
manufactured. Keep in mind that code numbers and/
or dates that appear on the actual lamp or luminaire
usually are warranty related and do not necessarily
indicate the date and time of manufacture.
The reason you should select equipment from different
batches or runs is simple: lamp and luminaire
manufacturers usually make mistakes between
batches, not between individual lamps or luminaires.
Changes in raw materials, manufacturing methods or
worker inspection can lead to a bad run of equipment
before the problem is realized and corrected. These
bad runs will have an inordinate percentage of defective
units, whereas a good run may have only an occasional
oddball defect. Your test group should contain units from
all runs or batches in your inventory. If a bad unit is
found, further testing of units in that batch may uncover
a defective run that could play havoc with your spot
replacement program.
Visual Inspection
Before performing any electrical tests, lamps and
luminaires should visually be inspected for manufacturing
defects and damage due to shipping and handling.
Lamps: Inspect all lamps for the following:
• Broken internal welds.
• Bent arc tube supports that allow an arc tube
misalignment of more than 3°.
Loose screw base.
Broken arc tube mountings.
Broken electrodes.
Defective vacuum seal indicated by a white, chalklike deposit inside the lamp envelope. (This condition
may occur before or after the electrical test.)
Luminaires: Inspect all luminaires for the following:
Broken refractors.
Broken lamp sockets.
Broken or bent luminaire housing.
Loose or broken screws.
Broken or damaged electrical components.
Good optical assembly seal and alignment.
Smooth, working housing hinges, hinge keepers and
• Any loose electrical connections, kinked wire,
abraded wire, stripped or overtight terminal block
connections, etc.
• The presence of wildlife shields, fitter clamps and
all equipment and options predescribed by the
luminaire manufacturer’s presubmitted sample.
Any damaged or missing component on the lamp or
luminaire is reason for rejection. If it is apparent that
shipping and/or handling damage has occurred, the
source of the damage should be determined and the
responsible parties notified.
Lamps and luminaires that pass visual and mechanical
inspection are now ready for electrical testing. HPS
lamps, photocontrols and luminaires can be pretested
in one of three ways:
1. By using a test group of sample lamps and luminaires.
2. By testing lamps and luminaires using a special HPS
lamp/luminaire test bench.
3. By testing photocontrols using the test bench.
The high-voltage spike required to start an HPS lamp
makes electrical testing of the luminaire somewhat of
a problem. Testing for this very short duration voltage
pulse normally would require the use of an oscilloscope.
But an oscilloscope is not a practical piece of test
equipment when testing a luminaire in the field. The
quality and cost of the scope needed to accurately
display this voltage pulse is quite high. Even when
accurately displayed, the short duration spike is very
hard to see on the scope screen, particularly in daylight
or bright sun. Plus the oscilloscope is difficult to
maneuver and set up in a truck bucket, and impossible
to use from a stepladder or from climber’s hooks.
Voltmeters are of limited use when troubleshooting HPS
luminaires. They can be used to check minimum opencircuit voltage at the lamp, but only after the starting
circuit lead has been disconnected. Otherwise, the
extremely high starting pulse voltage could damage the
Even if the voltmeter is protected against the highvoltage pulse, its voltage reading only will indicate that
voltage is present. It cannot determine the load-carrying
capability of the circuit being checked. For example, if
the screw to the center contact of the socket becomes
loose, the HPS light bulb may not light when screwed
into the socket. However, if the leads of the voltmeter
were placed across this connection, the meter would
read voltage. A low-grade connection may allow the
voltmeter to read a voltage, but limit the current to levels
below those needed to operate the lamp.
Neon Lamp Testers
Various luminaire and lamp manufacturers also sell
special neon testers designed to troubleshoot and test
HPS systems. These testers may use from one to three
neon lamps. The single-neon lamp type usually
indicates socket voltage or spike voltage. The two- and
three-neon lamp testers are designed to indicate the
presence of both socket voltage and spike voltage. The
two-lamp tester indicates a spike on one half cycle only,
while the three-lamp tester supposedly indicates a spike
voltage on both half cycles of the AC waveform.
Using these testers can be confusing and results are
not always accurate. For example, the neon can be lit
by stray voltages from various sources such as highvoltage transmission lines, transformers and other
devices emitting static voltage. And like a voltmeter, a
neon tester, even when operating correctly, indicates only
the presence of a voltage. It cannot tell you if the circuit
being tested has a load-carrying capability. The circuit
being tested could have poor or marginal connections.
Also, some HPS lamp starters are designed to produce
a starting spike on only one of the two AC current half
cycles. Others are designed to produce spikes on both
half cycles. A single luminaire manufacturer may use
both systems, and there are no markings on the
luminaire to indicate which system is being used. This
means that if you test a one-half cycle starter with a
three-neon lamp tester designed to signal the presence
of spikes on both half cycles, the tester automatically
would indicate a defective starter.
There also are several specifications that must be met
in the starting voltage spike. The spike must be between
the 2500- to 4000-volt ranges. It must be within +20
electrical degrees of the center of the half-cycle point,
and its duration must be from 1 to 15 microseconds at
2150 volts. The neon tester does not indicate the spike’s
conformity to any of these parameters.
Luminous Wattmeters
One of the most reliable, meaningful and economical
pieces of test equipment for HPS lamps is the
incandescent lamp. A simple luminous wattmeter can
be made using a 250-volt, 50-watt, rough service
incandescent lamp equipped with a mogul-to-mogul
lamp socket extender and fitted with a medium-tomogul socket adapter (Figure 25). A 250-volt
incandescent lamp is used because it can handle the
minimum open circuit voltages of all HPS lamps, except
the 1000-watt HPS lamp. The 50-watt lamp size
produces a dimmer-burning bulb that will not blind you
during testing. A 100-watt incandescent would be too
bright. The 50-watt bulb also is smaller and cooler to
handle. Finally, the rough-service-grade incandescent
allows for testing in luminaires where high vibration is
encountered without undue breakage of the lamp
filament. It should be remembered, however, that these
lamps are not indestructible. Tuffskin® coating for the
lamp is advisable when the lamp is to be used in
hazardous locations or adverse environments. Be sure
your luminous wattmeter is using a known good lamp
before taking it into the field.
Most HPS lamps and their corresponding luminaires
are equipped with mogul bases and sockets. The 250volt, 50-watt incandescent lamp only is available with a
medium base. The mogul-to-mogul extender and
medium-to-mogul adapter are needed to properly install
the luminous wattmeter into the mogul base of the HPS
fixture. Mogul sockets are equipped with lamp retainers
and a locknut configuration that prevents the screwedin lamp from vibrating out of the lamp socket.
When troubleshooting, it is desirable to mechanically
stress the lamp socket by installing the lamp as tight
as practical. A light lamp base-to-socket contact may
not reveal problems at this connection. This causes
some problems when adapting the incandescent lamp
to the HPS mogul socket. If only a medium-to-mogul
adapter were used, it would be difficult to install the
incandescent tight enough to stress the connection.
The weaker incandescent lamp medium base-tomedium socket connection at the adapter may become
stressed and break, shattering the lamp. Usually, there
is little problem screwing the adapter into the mogul
socket. The problem is in safely removing it without
breaking the incandescent.
The solution is to screw the incandescent into the
medium-to-mogul adapter and then screw the mogul
end of the adapter into one end of a mogul-to-mogul
extender. The other end of the mogul-to-mogul extender
is then screwed into the mogul socket of the HPS
luminaire. It is possible to tightly grip the body of the
extender without damaging or stressing the
incandescent lamp or its base.
Note: While the medium-to-mogul adapter is a
common piece of hardware, the mogul-to-mogul
extender can be more difficult to find. One source for
the extender is the Leviton Manufacturing Company
Inc. Order through your electrical distributor.
Some lower-wattage HPS lamps and luminaires can
be equipped with medium bases and sockets that
match the incandescent lamp. The luminous wattmeter
can be screwed directly into these sockets.
Advantages of the Luminous Wattmeter: The
luminous wattmeter has several distinct advantages as
an HPS troubleshooting tool. It does not require a starter
for operation and it gives a visual indication of the
circuit’s ability to carry current. This makes it an
excellent tool for determining the cause of luminaire
outages in the field. The following is an example of
how the luminous wattmeter can be used to
troubleshoot an outage:
1. Begin by testing the photocontrol with the hand test
explained earlier. Replace if defective.
2. If the outage is not corrected, replace the HPS lamp
with a known good lamp.
3. If the known good lamp does not start, remove it
and install the luminous wattmeter. As you install
the luminous wattmeter, do not stop until the base
is fully bottomed out in the socket and mechanically
stressed. In some cases, the lamp may turn ON
partway in and then turn OFF again when tightly
installed. The lamp also may start to blink or turn
ON and OFF. This could indicate a loose screw in
the socket, or a bad base-to-socket connection or a
shorting of the lamp socket connector to the lamp
mounting bracket.
4. If the luminous wattmeter lights, it indicates that the
luminaire has a good power system-to-fixture
connection. Power is passing through the terminal
board, through the ballast and out through the wiring
and connections to the incandescent lamp. That
quickly lets you know all these possible trouble spots
are functioning correctly.
Since the incandescent works and the HPS lamp
does not, all evidence points to a defective starter.
Replace the starter and install the HPS lamp. In the
vast majority of cases, the lamp will now start. If it
does not start, replace the entire luminaire if no other
physical damage is found.
5. If the luminous wattmeter does not light when
installed in step 3, it indicates other problems such
as an open connection at a luminaire component, a
blown line fuse, or no power to the luminaire. Check
for burned or damaged fixture components and for
loose or disconnected electrical connections. Use
a voltmeter to check supply voltage. Is it the same
as the fixture is rated for? Check for correct and
functional photocontrol operation. You also should
check for a missing or defective capacitor bleed
resistor across the regulating capacitor when a twocoil regulating ballast is used.
Note: In a rare case when the bleed resistor is
open, the charge on the capacitor can cause the
starter to remain in the OFF position and the
lamp will not start.
When the luminous wattmeter does not burn, leave the
luminous wattmeter in the luminaire and troubleshoot
the problem until the incandescent can be made to light.
If the problem cannot be found, replace the luminaire.
Two Problem Outages: Occasionally, two distinct
problems could be the cause of the outage. For
example, a given luminaire could have an intermittent
power connection to the fixture. The arcing caused by
the bad connection also could cause a starter circuit
failure. When the known good HPS lamp is installed in
such a situation, it will not start. When installed in its
place, the luminous wattmeter also will not light.
When this condition occurs, leave the luminous
wattmeter in the luminaire until it is made to burn. For
example, repairing the bad connection would allow the
luminous wattmeter to light. Then, it could be assumed
the cause of the problem was the bad connection, but
when the known good HPS lamp is reinstalled it does
not start. Once reaching this point in the troubleshooting
procedure, it becomes apparent that two problems exist.
The fact that you were able to make the luminous
wattmeter burn, but not the HPS lamp, indicates a
possible defective starter. The important fact to
remember is to leave the luminous wattmeter installed
until it burns. Attempting to find intermittent connections
and starter-related problems by only an HPS lamp could
lead to considerable confusion and wasted time.
Special Problems: In rare cases, a luminaire ballast
or capacitor failure may allow the luminous wattmeter
to burn, but not allow the HPS lamp to ignite and operate
even when a known good starter is installed. However,
this is a very rare situation that most service technicians
never will encounter.
Voltage Pulse Concerns: There is no need to be
concerned over the possibility of the 2500- to 4000volt starting pulse voltage spike damaging the luminous
wattmeter or causing it to explode. The spike is of very
short duration and very low current. The incandescent
lamp harmlessly shorts out this starter output. The
luminous wattmeter has been used to troubleshoot
luminaires equipped with instant restrike devices
producing 12,000 to 14,000 restrike voltage pulses or
spikes with no harm to the incandescent bulb.
Caution: Always wear safely glasses when working
with light bulbs of any type because there is always
a possibility of a freak situation that may cause the
lamp to explode.
Mercury Vapor Test Lamp: Since a mercury vapor
lamp does not require a starter, it too can be used to
troubleshoot an HPS luminaire, although not as
effectively as an incandescent lamp. A mercury vapor
lamp requires 240 volts at the socket for starting. HPS
luminaires designed for 35- to 150-watt, 55-volt HPS
lamps only will provide 120 volts. In this case, the
mercury vapor lamp may start with 120 volts, provided
the ambient temperature is not too cold. Unlike an
incandescent luminous wattmeter, a mercury vapor test
lamp will not readily show varying degrees of brightness.
They also cannot be made to flicker when checking for
intermittent connections. Instead, the mercury vapor
lamp will drop out and cycle. For these reasons, it is
highly recommended you use an incandescent
luminous wattmeter to troubleshoot HPS fixtures.
After reaching a defective HPS luminaire location in
the field, a properly trained service technician should
be able to troubleshoot, repair or replace the defective
fixture within a 10- to 15-minute time frame. This 15minute service call relies on a consistent, logical
approach to troubleshooting, an understanding of HPS
operation and the proper use of test equipment. Make
certain you take a known good HPS lamp, a luminous
wattmeter and a voltmeter on all service calls.
The 15-minute service call is based on some very real
economic facts of life. It takes time to travel to the job
site and set up the lift truck or ladder. If the service
technician then spends much more than 15 minutes
servicing one particular luminaire, the cost of his or
her time begins to approach or exceed the actual cost
of the luminaire. If the problem cannot be pinpointed
and corrected in this time frame, the luminaire should
be removed and replaced.
The service technician also must take this opportunity
to quickly inspect the entire luminaire. Look for potential
future problems and repair them on this service call.
Take a minute or two to look for charred or heat-damaged
surfaces or photocontrol receptacle. Also check for
pinched wires and hot spots on ballasts that may signal
failure in the near future. Check the fixture mounting.
The housing should be level and all mounting bolts and
clamps should be present, tight and in good condition.
HPS Luminaire Failures
Following are common luminaire failures that may be
encountered in the field.
Outages: An outage is the most common type of failure.
The most common failed component is the lamp itself.
Replace the lamp in the outage fixture with a known good
HPS lamp. If the lamp does not come ON, remove it and
install the luminous wattmeter. Troubleshoot using the
luminous wattmeter as described in the previous section
to pinpoint starter, wiring, or other power-supply-related
problems. It should be noted that wiring problems are not
as common as starter problems. Also check for a missing
or defective capacitor bleed resistor (Figure 20). If line
voltage to the lamp is good and if there appears to be no
wiring or photocontrol-related problems, replace the fixture.
Bleed Resistor
If the lamp in question has reached its normal end-of-life,
this bump test will cause the burning lamp to turn OFF.
Reinstall a known good lamp and allow it to warm up for
several minutes. Reshock the lamp. If it turns OFF, check
the fixture wiring by probing with an insulated tool to locate
opens and shorts. Check that the ballast and capacitor
match the lamp rating, and be sure the capacitor is
correctly wired. If this fails to isolate the problem, replace
the luminaire.
If the vibration test of the suspect lamp does not cause it
to cycle, turn the photocontrol to the area where it will
receive the least amount of ambient light. Since a fixture’s
own light can sometimes reflect off of an object, such as
a tree or building, and cause the fixture to turn OFF and
then ON again after the lamp has cooled, be aware of
nearby reflective surfaces and shield the photocontrol if
necessary. Also, be sure the lamp is the correct lamp for
the fixture by checking the lamp inscription label against
that in the luminaire.
Dim Burners: A dim-burning or low-output fixture usually
is caused by having the wrong wattage lamp installed in
the fixture, such as a 55-volt lamp in a 100-volt fixture, or
a 100-watt lamp used in a 50-watt fixture, or a 150-watt
light bulb installed in a 70-or 100-watt fixture. Check and/
or install a new correct size lamp.
FIGURE 20. A missing or defective capacitor resistor
can cause a no-start problem.
Cycling: Cycling is the normal, end-of-life failure mode
for HPS lamps. To summarize, cycling can be caused by
a normal, end-of-life HPS voltage rise, an intermittent
electrical connection triggered by wind conditions or
vibration from traffic, a manufacturing defect in the lamp,
an overly sensitive photocontrol, heat damage to
photocontrol receptacle contacts or high ambient light level
tricking the control. A defective ballast or capacitor also
can cause cycling.
Quite often, when the service technician arrives at the
location of a cycler, the lamp will be operating properly.
This is because the conditions that may have been causing
the cycling, such as wind, traffic-induced vibration, or a
slight variance in line voltage, are not occurring at the
moment. If the lamp is no longer cycling, use the bump
test described earlier to induce a vibration in the lamp
and luminaire. With metal poles, it is possible to sufficiently
shock the fixture by striking the pole while standing on the
ground. When wood or concrete poles are used, it may
be necessary to moderately strike the fixture mast arm.
Low supply voltage also can cause a dim burner. Measure
the supply voltage across the terminals and make certain
it matches the rating on the ballast voltage label. Improper
wiring of a multi-tap ballast is another cause of low-light
output. Check and correct any miswiring.
On regulated ballast fixtures, a disconnected or defective
regulating capacitor also can cause a dim-burning
fixture. Be sure the correct capacitor is used and that it
is wired correctly.
Day Burners: A fixture that burns night and day usually
has a defective photocontrol. Replace the photocontrol.
If the problem persists, check for open wiring, usually the
white wire from the photocontrol receptacle is open. If the
problem still exists, replace the fixture. Also replace the
fixture if there is evidence of heat damage to the
photocontrol receptacle.
Short Life Lamps: If the lamp burns out shortly after being
installed, check for proper match-up of lamp, ballast and
capacitor ratings. Check a similar, properly operating
luminaire for the correct capacitor size or refer to
manufacturer’s specifications. Finally, check the wiring
diagram against the actual wiring to ensure the fixture
has not been miswired.
Unknown problems: If the exact nature of the problem
is unknown, troubleshoot the fixture as if it were an outage.
Cover the photocontrol and listen for a sharp click when
the control operates. Change the control if it growls. If the
lamp does not come ON, substitute a known good HPS
lamp. If this lamp does not operate, test and troubleshoot
using the luminous wattmeter.
a very short period of time. A cycle occurs each time a
pattern of variation completes. The number of times a
cycle occurs each second is the frequency (Hertz) of
the voltage and current. Voltage and current in the
United States and most of the world completes 60
cycles each second. Direct current, such as that
generated by storage batteries, is not cyclical.
If the known good HPS lamp does light, test for cycling
problems. If this is the first service call on this luminaire,
replace the lamp and photocontrol. If it is the second call,
remove and replace the fixture.
Ion. An atom or molecule that has an electrical charge.
The following definitions are offered to develop a
practical understanding of the electrical principles
involved in lighting. In some cases, the definition may
contain a slight technical error to make the definition
more straightforward and convey the general meaning
of the term. Many electrical principles are compared to
familiar mechanical actions to more clearly present an
idea or concept.
Ballast Short Circuit Current. This is current
measured in the HID lamp circuit with the ballast
energized and the lamp socket shorted out (socket
shell-to-socket center contact.)
Conductor. A material such as copper or aluminum
that supports the flow of current. It is important to
remember that your body is an excellent conductor of
electricity. Water also is a great conductor. Air and
insulating materials such as rubber and plastics are
poor conductors.
Current. Electricity in motion. It is the flow of electrons
through a conductor. Voltage is the force, or pressure,
that drives the current through the conductor. Current
flows only between points having a difference of potential.
The ampere, or amp, is the unit of current measurement.
Electric Circuit. A path or a group of interconnected
paths capable of carrying electric current.
Electron. A single, microscopic particle with an
electrical charge. It can be compared to a drop of water
in a water pipe. In atoms, electrons orbit around the
nucleus. Current flow occurs when electrons break free
of their orbits and jump from atom to atom.
Lamp. The actual assembly that includes the glass
bulb, arc tube, screw base, etc. It should not be
confused with the luminaire (see below). The lamp is
commonly referred to as the light bulb.
Luminaire. The complete lighting unit. Its metal housing
contains the lamp, socket, wiring, starter, ballast,
photocontrol receptacle, optical assembly and all other
components needed to generate lumen output. Many
times the luminaire simply is referred to as the fixture.
Ohm’s Law. The basic law of electricity. It states that
Voltage =Current x Resistance. This equation can be
used to find any unknown variable when the other two
variables are known.
Open Circuit. A break or disconnection in the wiring or
at a connection. Current does not flow in an open circuit.
It is commonly expressed as voltage measured at the
lamp socket without a lamp in the socket.
Power. The rate at which electrical energy is used. The
watt is the unit of power measurement. Power requires
voltage and current; that is, electric pressure
accompanied by a flow of electrons. Power can be
calculated using the following equation: Power =
Voltage x Current. Wattage results in heat and light.
Power Factor. The time difference between the
presence of voltage and the flow of current. It can be
compared to air in the water line of a pumping system.
You turn on the faucet and there is pressure (voltage),
but a burst of air is all that comes out before the water
(current) begins to flow. Power factor is high (90 % or
better) when there is almost no delay in the current
flow. Power factor is normal (about 50%) when current
flow is delayed. See point N in Figure 21.
Resistance. Resistance limits or controls the flow of
current. All conductors offer some resistance to current
flow. Resistance can be compared to the amount of
friction between the flowing water and the pipe walls in
a plumbing system.
Fixture. See “Luminaire.”
Frequency. In lighting applications powered by
alternating current, voltage and current vary rapidly over
Secondary. The customer side of a power company’s
distribution transformer where the service drop for the
luminaire is connected.
Short Circuit. An accidental path of low resistance
that passes an abnormally large amount of current. A
short often occurs as a result of improper wiring or
broken insulation.
Voltage. Voltage is electric pressure. It can be compared
to water pressure in a plumbing system. It also is a force,
referred to as electromotive force (emf). Other terms
used for voltage are potential and potential difference.
The volt is the unit of electric pressure.
Watts Loss. The difference between the amount of
power supplied to a luminaire (ballast and lamp) and
the amount of power actually used by the lamp itself.
177 V
Power Factor 50%
177 V
Time 1/60 Second
This illustration represents a 120-volt waveform.
The voltage ranges from zero to 177 volts to zero to 177 to zero 60 times a second.
The average voltage is 120 volts.
FIGURE 21. Graphic representation of normal power factor ballast.
This requirement is for lag circuit (regulated or non-regulated) ballast designs:
Base ...................................................... Mogul Screw
Bulb ............................ E23-1/2 Borosilicate Type 772
Arc Tube
Maximum Overall Length .............................. 197mm
Maximum Diameter ...................... 76.48mm (3.011”)
Arc Tube
Light Center Length ................................. 123 ± 3mm
Arc Length ................................................ 37 ± 1mm
Maximum Bulb Temperature ......................... 400° C1
Maximum Base Temperature ........................ 210° C1
A. Wattage
Rated Watts ............................................................................................................................. 150 watts
Permitted Operating Range for Rated Lamp Life ............................... Min. 112.5 watts (Max. 175 watts)
B. Voltage 2
Rated Lamp Voltage (Design Center) ..................................................................... 55 volts at 150 watts
Initial Lamp Voltage Range at 100 Hours .......................................................... 48-62 volts at 150 watts
Maximum Lamp Voltage3 ............................................................................................................ 88 volts
C. Current
Operating Current ..................................................................................................3.2 amperes nominal
D. Operating Limits
The trapezoid shown below illustrates lamp voltage-wattage limits. For a ballast to meet the lamp operating
requirements, its characteristic curve must intersect each of the lamp voltage limit lines at points between
the wattage limit lines and must remain between these wattage limit lines throughout the full range of the
lamp voltage.
Maximum temperatures allowed under conditions where published performance ratings apply.
Lamp voltage is determined by operating the lamp on a linear inductor of approximately 31 ohms for one hour, with the line voltage adjusted to maintain
the lamp at 150 watts.
Lamp voltage may rise reaching 88 volts near the end of life.
TRAPEZOID — 150W HPS, 55V Lamp
G. Other Considerations
1. High Pressure Sodium lamps, like other
discharge lamps, exhibit reignition
phenomena that are influenced by ballast
design. Certain ballast designs can lead to
distinctive effects such as:
The required ballast characteristics must be
provided with the ballast operating over the full range
of line voltage for which it is designed.
A. Minimum Ballast Open-Circuit Voltage
(O.C.V.): 110 Volts (RMS)4
a. Strong visual lamp flicker.
B. Starting Pulse Requirements
b. High lamp reiginition voltage.
1. Pulse peak voltage:
c. Lamp extinction and/or unusual
sensitivity to line voltage fluctuations.
Min. 2500 volts
d. Pulse voltage required to start lamps in
excess of the minimum starting-pulse
Arc-over in the lamp structure will not occur
at peak voltage less than 4,000 volts.
2. Pulse width measured at 2250 volts:
Min. 1 microsecond
3. Pulse repetition rate:
NOTE: Any such observations should be cause for concern as the
system life and performance may be adversely affected.
2. Published lamp performance ratings do not
apply when High Pressure Sodium lamps
are operated on direct current or at
frequencies other than 50-60 hertz.
Min. 50 per second
4. Pulse peak current:
Min. 0.2 amp
5. The starting pulse should be located within
20 electrical degrees of the peak of the
open circuit voltage for the most reliable
lamp starting.
A. Lamp Voltage Rise Limits
The evacuated outer bulb of the lamp makes
the lamp insensitive to ambient temperature.
However, care must be used in luminaire design
to avoid reflecting energy to the arc tube
appendage (always at the lower end for both
base-up and base-down lamps). This affects
the temperature of the sodium-mercury
amalgam and results in a change in lamp
characteristics. The lamp voltage of new lamps
(48-62 volts at 150 watts) must not increase
more than 4 volts when going from stabilized
bare-lamp operation to stabilized operation in
the luminaire. Fixture effects are best evaluated
by operating the lamp on a linear reactor of
approximately 31 ohms with the line voltage
adjusted to maintain the lamp at 150 watts.
Additional information is available upon request.
6. Lamp starting is not affected by ambient
C. Lamp Current During Warm-Up
Min. 3.2 amp (RMS)
Max. 4.8 amp (RMS)
D. Maximum Current Crest Factor: 1.8
E. Ballast Marking
The ballast should be clearly labeled to indicate
the range of line voltage for which it is designed,
as published lamp performance ratings do not
apply when the line voltage is outside these
Short-Circuit and Open-Circuit Current
To protect the ballast against unusual lamp
failure modes, the ballast should be capable of
operation under either an open or short circuited
condition for extended periods.
B. Line Voltage Designation
For integral-ballasted luminaires, labeling
prominently displayed for the user should be
used to indicate the range of line voltage for
which the ballast is designed, as published lamp
ratings do not apply when the line voltage is
outside these limits.
NOTE: Starting pulses are not required and are not desirable after
a stable arc has been established.
Minimum value required for stable lamp operation throughout life. When
designing the ballast, consideration must be given to avoiding lamp
extinction with sudden line-voltage dips.
Outer Envelope
This requirement is for lag circuit (regulated or non-regulated) ballast designs:
Arc Tube
Base ...................................................... Mogul Screw
Bulb ............................... E18 Borosilicate Lead Glass
Overall Length ........... 244 ± 4mm (9-5/8” Maximum)
Diameter .......................... 57 ± 1mm (2-1/4” Approx.)
Light Center Length ........ 146 ± 3mm (5-3/4” Approx.)
Arc Length ........................ 87 ± 2mm (3-3/8” Approx.)
Maximum Bulb Temperature ........................... 400° C
Maximum Base Temperature .......................... 210° C
Arc Tube
A. Wattage
Rated Watts .............................................................................................................................. 400 watts
Permitted Operating Range for Rated Lamp Life ................................... Min. 300 watts (Max. 475 watts)
B. Characteristic Voltage1
Rated Voltage (Design Center) ............................................................................. 100 volts @ 400 watts
Voltage Range at 100 Hours ............................................................................ 90-115 volts @ 400 watts
Maximum Lamp Voltage2 ........................................................................................................... 140 volts
C. Current
Operating Current (RMS) ........................................................................................ 4.7 amperes nominal
Current During Warm-Up (RMS) ................................................... Min. 4.7 amperes (Max. 7.0 amperes)
Current Crest Factor .................................................................................................................. Max. 1.8
D. Operating Limits
The trapezoid shown below illustrates lamp voltage-wattage limits. For a ballast to meet the lamp operating requirements, its characteristic curve must intersect each of the lamp voltage limit lines at points
between the wattage limit lines and must remain between these wattage limit lines throughout the full
range of lamp voltage.
1 Lamp voltage is determined after operating the lamp on a linear
inductor for one hour. The line voltage is adjusted to control the
lamp wattage. The lamp characteristic curve is the volt-watt curve
for the equilibrated lamp. The characteristic voltage is the lamp
voltage at rated watts.
2 Lamp characteristic voltage may rise reaching 140 volts near the
end of life.
TRAPEZOID – 400W HPS, 100V Lamp
The required ballast characteristics must be
provided with the ballast operating over the full range
of line voltage for which it is designed.
A. Minimum Ballast Open Circuit Voltage
(O.C.V.): 195 Volts (RMS)
This is the minimum value required for stable
lamp operation throughout life. When
designing the ballast O.C.V., consideration
must be given to avoid lamp extinction with
sudden line-voltage dips. A ballast lamp testing
procedure (measurement of ballast drop-out
point for High Pressure Sodium ballasts) is
available from the OEM fixture liaison and
technical services section.
B. Starting Pulse Requirements
The ballast should be clearly labeled to indicate
the range of line voltage for which it is designed
as published lamp performance ratings do not
apply when the line voltage is outside these limits.
D. Short-Circuit and Open-Circuit Current
To protect the ballast against unusual lamp
failure modes, the ballast should be capable of
operation with an open or short circuit condition
for extended periods.
E. Other Considerations
1. High Pressure Sodium lamps, like other
discharge lamps, exhibit reignition
phenomena that are influenced by ballast
design. Certain ballast designs can lead to
distinctive effects such as:
Measured across the socket terminals using a
high frequency scope and high impedance probe.
a. Strong visual lamp flicker.
1. Pulse Peak voltage:
Min. 2500 volts
Max. 4000 volts
2. The 4kv maximum is set to prevent internal
arc-over. the starting circuit shall limit the
pulse to a maximum of 4kv. If the starting
circuit is turned on at the high point on the
power distribution voltage wave, an
abnormal transient can occur. The starting
circuit must limit high transients.
3. Pulse width measured at 2250 volts:
Min. 1 microsecond
Max. 15 microseconds
4. Pulse repetition rate:
Min. 1 per cycle
5. Pulse peak current:
Min. 0.2 amperes
6. Pulse position: For near sine-wave O.C.V.
within 20 electrical degrees of the center of
the half cycle for reliable starting.
7. The pulse must be applied to the center
terminal of the lamp base.
8. Starting pulses are not required after the
arc has been established. To avoid radio
frequency interference and sub-standard
lamp performance, it is recommended that
the pulsing circuit be de-energized during
9. Lamp starting is not affected by ambient
C. Ballast Marking
b. High lamp reiginition voltage.
Lamp extinction and/or unusual
sensitivity to line voltage fluctuations.
d. Pulse voltage required to start lamps
in excess of the minimum startingpulse requirements (Section 3B).
NOTE: Any such observations should be cause for concern as the
system life and performance may be adversely affected.
2. Published lamp performance ratings apply
only when High Pressure Sodium lamps
are operated on 50-60 hertz.
A. Lamp Voltage Rise Limits
The evacuated outer bulb of the lamp makes
the lamp insensitive to ambient temperature.
However, care must be used in luminaire design
to avoid reflecting energy on the arc tube
appendages. This affects the sodium-mercury
amalgam and results in a change in lamp
characteristics. The lamp voltage of new lamps
(90-115 volts at 400 watts) must not increase
more than 10 volts when going from stabilized
bare-lamp operation to stabilized operation in
the luminaire.
B. Line Voltage Designation
For integral-ballasted luminaires, labeling
prominently displayed for the user should be
used to indicate the range of line voltage for
which the ballast is designed, as published lamp
ratings do not apply when the line voltage is
outside these limits.
A. Breakdown Voltage
The internal clearances of typical mogul sockets
are such that if an arc-over occurs, a destructive
power arc will be sustained by ballasts meeting
the criteria stated below. For this reason, the
internal breakdown voltage of the socket should
provide an adequate margin of safety, under
the environmental conditions anticipated.
This can be measured by applying a 50 to 60 Hz
sinusoidal voltage wave form between the center
pin and shell terminations of the socket with a
dummy 400-watt High Pressure Sodium ceramic
base inserted. The voltage should be increased
from zero at a rate of no more than 4kv/min.
until breakdown occurs. The peak voltage at the
point of breakdown should be 7kv. This test is
equivalent to a 5000 volt (RMS) high pot test.
Perform the test on the socket separately.
American Electric Lighting
©2004 Acuity Lighting Group, Inc., 10/04
Form No. 1315.29
Acuity Lighting Group, Inc.
1335 Industrial Boulevard, Conyers, GA 30012
Phone: 800-754-0463, Fax: 770-860-3255
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