2.1 Quartz discharge tube. Osram HQI-E 150 W/NDL CL
advertisement
6
Ceramic arc tubes can be produced with smaller dimensional tolerances, reducing the variation in lighttechnical and electrical parameters.
Ceramic is less susceptible to attacks from the aggressive metal halide filling and is less permeable for filling particles, resulting in a considerably longer service life compared to quartz tube lamps.
Ceramic arc tubes are now available in various different forms: the original cylindrical version and the improved round version.
Variation possibilities of the Colour Temperature
T n
CRI
Daylight
Neutral White
Neutral White de luxe
Warm White de luxe
2.2.1 1st generation: cylindrical form
In the first version, the ceramic arc tube was designed in a cylindrical form, based on the production technology for the high-pressure sodium lamp. The arc tube was made up of cylindrical sub-sections sintered together. The arc tube consisted of a relatively thick plug at either end of the tube: this was necessary for the durability and functioning of the tube.
Fig. 2a: Generation of the desired Spectral Distribution
Components in order to achieve high luminous Efficacies and good Colour Rendering
2.2.2 2nd generation: freely moldable ceramic,
POWERBALL ®
2.1 Quartz discharge tube
The discharge tubes in 1st-generation metal halide lamps are made of high purity quartz glass. This quartz material allows for stable operation at high temperatures, is resistant to sudden changes in temperature and is transparent. The well proven HQI lamps are produced in various different forms using this technology.
H
Q
I
...
...
...
Hydrargyrum (Greek-Latin for mercury)
Quartz
Iodide
• Well proven lamp technology
• Wide wattage range 70 W – 2000 W
• Colour temperatures up to 7250 K
• Good optical properties thanks to transparent discharge tube
A second step with changed production technology permitted production of freely moldable tube geometries. This made it possible to produce round ceramic arc tubes with a constant wall thickness – the
POWERBALL ® arc tubes. The round form and constant wall thickness brought considerable advantages. The possibility of further increasing the wall temperature improves luminous efficacy and colour rendering. The absence of the thick plug at the end of the tube reduces light absorption in this area, resulting in a higher luminous flux with more uniform irradiation characteristics. There are fewer differences in the wall temperature between the various burning positions and therefore also smaller differences in colour between the burning positions. The reduced ceramic mass of the round tube enables the tube to heat up faster, reaching the photometric values more quickly. Similarly, when the lamp goes off, warm re-ignition is possible more quickly because the required cooler starting temperature for normal ignition devices is achieved faster.
2.2 Ceramic discharge tube
The use of arc tubes made of ceramic material further enhanced some of the metal halide lamp’s properties.
Ceramic can withstand higher temperatures than quartz glass. This permits higher wall temperatures thereby evaporating more of the metal halide salts into the gas arc and allowing for more efficient use of the chemicals. Ceramic lamps offer improved luminous efficacy and colour rendering as a result.
The uniform wall thickness and round shape produce a more even temperature curve along the inner tube wall as shown in Fig. 3, based on the temperature shown in colours diagram. The steeper temperature gradient in the cylindrical ceramic favors chemical transport processes. During this process, aluminum oxide ceramic dissolves in the liquid metal halide melt and settles at cooler points of the arc tube. If erosion from the wall goes too far, this can lead to leakage in the tube, causing the lamp to fail. Failures due to so-called
“ceramic corrosion” are thus less likely to occur in lamps with round ceramic tubes.
9000 h
Solution of
Alumina in MH-melt
= Corrosion
Transport of soluble alumina in
MH-melt
Convection
Condensation of Metall Halides
Evaporation of Metal Halides
Deposition of alumina by saturation of HM-melt due to cooling
1100
1060
1020
980
940
Fig. 3: Comparison of ceramic corrosion between the different tube forms
12000 h
Convection
Evaporation of Metal Halides
The advantages of POWERBALL ® technology compared to cylindrical solutions
• Better maintained luminous flux throughout the service life
• Improved color rendering, particularly in the red
• Improved color stability during the service life
• More uniform operation independent of burning position
• More constant luminous intensity distribution
• Faster start-up behavior
Conden-
sation of
Metal Halides
7
advertisement
