LED lighting Technical Guide
Features of LED lights
A fluorescent lamp and Halogen have wide wavelength distribution,
but LED includes a specific emission of light wavelength in each.
When selecting a wavelength, please consider the points below:
■ High efficiency, low power consumption
■ Low total running cost
■ Very fast response time
■ Durable against switching
Elements required for image processing Lighting:
3. Stable illumination intensity
A large change in illumination intensity over time or due to
the surrounding environment can cause inspection
accuracy to decrease.
Even with a low initial cost, light which needs frequent
maintenance will increase long-term costs.
Installing long lasting and stable illumination reduces the
total running cost.
2. Even lighting
Wavelength (nm)
Even illumination intensity in the imaging area is
required when extracting the inspection item by LED light.
Unevenness of illumination intensity prevents correct
reflection of the object's surface condition and causes
unstable inspection.
Scattering Rate:
Comparison list of LED lights and other lights
Light source
LED Lights
Halogen
Fluorescent Lamp
Xenon
Life
Brightness
Wave length selection Shape flexibility
Evenness
Directivity
Cost
Switching characteristics Power consumption
The reason the LED light is selected as a light source for image processing is because it facilitates optimal lighting for inspection.
Peak Wavelength
White
Response speed
Power consumption
Comparison with the lifetimes of other power sources
Ultraviolet
Blue
Green
Red
Infrared
HALOGEN
Fluorescent
Lamp
LED
HALOGEN
LED
Illuminance drift chart by Duty setting
Measured how much the illuminance changed from starting point
with each Duty (10%, 50%, 100%) of power supply.
Duty
Cycle [sec]
ON Time [sec]
1
0.5
Duty 10%
Duty 50%
2009
Duty 100%
Inspection for scratches, etc.
Visual Inspection, etc.
Used for backlight, etc.
Permeable Illumination
Approx. 9
Approx. 8
Approx. 4
Approx. 2.5
1
Approx. 0.4
Wavelength (nm)
Time (Min)
Duty 10%
Duty 50%
Duty 100%
Wavelength (μm)
Spectral Sensitivity Characteristic of a Camera
rep. value
1
1
Relative Strength
Relative illuminance (%)
Time (Min)
27
1
0.1
OPDR-90-50W (WHITE)
Relative illuminance (%)
OPDR-90-50R (RED)
Inspection for fine scratches, etc.
Scattering Rate
Spectral Luminous Efficiency Curve
(Ambient temp.=25℃)
Duty setting
Condition:
375nm
400nm
470nm
525nm
660nm
850nm
Main Inspection Uses
Color treating, etc.
Halogen Spectral Distribution
Visible light is light that can be seen by human eyes. Visible light generally
has a wavelength of between 380nm and 780nm. Light with a wavelength
higher than 780nm is infrared and light with a wavelength lower than 380nm
is ultraviolet.
The human eye is most sensitive to green light with a wavelength of 555nm.
Sensitivity decreases if the wavelength increases or decreases. The sensitivity
curve when this 555nm is counted as 1 is called the Spectral Luminous
Efficiency. Measurements of brightness such as lux and cd/m2 are coefficients
of this Spectral Luminous Efficiency.
The spectral sensitivity of a camera does not necessarily have the same
distribution as the Spectral Luminous Efficiency. The sensitivity of some
cameras is set to match infrared or ultraviolet ranges. When setting Lighting,
please check that the light distribution matches the camera you are using.
LED
HALOGEN
Wavelength (nm)
The comparative scattering rate for each wavelength is shown when the red
scattering rate is counted as 1. The scattering rate increases as the wavelength
gets shorter.
When using a wavelength with a high scattering rate, it becomes easier to
observe scattering light from the object surface. However, please note that
when using a wavelength shorter than green, the camera's sensitivity may
decrease.
When using a long wavelength, permeability increases. Infrared lighting, in
particular, is effective for inspecting permeability.
Relative Strength (%)
For a stable image processing inspection, the imags to be
inspected must be as clear as possible.
The LED lights create an image with a high SN rate, by
selecting the optimal shape and wavelength for the target
object, which leads to high inspection quality.
Relative Strength
1. Image with high SN rate
Fluorescent Spectral Distribution
Count (%)
Relative Emission Strength (%)
■ Flexible in shape
■ Allows light directivity
■ Selectable wavelength
■ Long life
Emission Spectral Distribution
Wavelength (nm)
During image processing, because generally a CCD or CMOS camera is used,
illumination brightness must be evaluated with the camera, and not human eyes.
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LED Lights selection guide
Points when setting the Lighting
The Visual Field of Coaxial Lighting
When setting the Lighting it is necessary to consider several factors.
Even when using the same Lighting, if the set height is different the captured
images are completely different. Also, if the Lighting wavelength (color) is
different, the images change. When setting Lighting, please consider the
points below:
Coaxial Lighting is a type of Lighting in which the surface emitting part of the
LED emits light along the same axis as the camera lens, via a half-mirror. The
effective visual field of coaxial lighting is dependent upon the distance
between the camera and object (OD), the distance between the Lighting and
object (LOD), and the size of the light emitting surface. If the OD increases,
the visual field grows, but if the LOD increases, the visual field shrinks. The
method of calculating the effective visual field is shown below. It is necessary
to keep the object within the effective visual field, especially for objects with a
high reflectance. This effective visual field is calculated based on the size of
the light emitting surface. It is recommended that you set a sufficient visual
field, taking into consideration the lower luminance in the surrounding area.
Testing Conditions
Additive Primary Colors
By combining the light of red, green and blue (additive primary colors) you
can create other colors. Green(G) and blue(B) make Cyan(C), B and red(R)
make Magenta(M), and R and G make yellow(Y). By combining R, G, and B
lights of the same strength, white(W) is created. Combining colors in this way
is called additive color mixing.
Colors can also be created by absorbing parts of light. C absorbs R, M
absorbs G, and Y absorbs B. C, M, and Y absorb all of the light, and black(K)
is created. Combining colors in this way is called subtractive color mixing
and CMY are called subtractive primary colors.
White Lighting
Subtractive Primary Colors
The color pattern using CMY is shown below. Also, color images using white,
red, green, and blue and the monochrome image are shown. The contrast
varies depending on the color of the light. When recognizing the object during
image processing, it is important that there is sufficient contrast. During
image processing, please select a light color where there is a large contrast
between the object color and background color, referring to the color patterns
below.
Testing System Specs
Lighting Specs
・Testing Items
・Camera System
・Lighting System
・Extraction Point of Features
・Optical Specs
・Configuration
・Surface Condition
・Visual Field
・Size
・Configuration
・Line Speed
・Wavelength
・Reflectance, Transmittance
・Method of Sending
・Parallelism
・Quality of Material
・Dimension Restrictions
・Brightness
etc.
etc.
etc.
Calculating the effective visual field
Lens
For the OPCX-50R:
How to Use and Maintain LED Lighting
To get the best performance from LED Lighting:
Virtual light
emitting surface
1. Please avoid using LED lights in a high-temperature environment.
Doing so may lower the illuminance and facilitate deteriortion.
Red Lighting
Green Lighting
Blue Lighting
If the LED element becomes heated, illuminance is reduced and general
performance deteriorates. The half-life of the illuminance of an LED
element is said to be about 20,000 hours (Typ.), but if the element is
continuously used in a high-temperature environment, its performance may
deteriorate quicker.
OD: x
Distance
from light
emitting
surface: a
Dimensions of
light emitting
surface: b
2. To prevent illuminance reduction and performance deterioration
due to the generation of heat:
Color Image
●Improve the heat dissipation of the LEDs.
・ Mount the Lighting on a bracket with good heat conductivity.
・ Install a ventilating device.
・ Install a fan.
We recommend creating a cool environment which allows easy heat
dissipation.
Surface of object
Distance from
virtual light
emitting
surface: y + a
Effective visual
field: z
● Turn the Lighting on only when imaging.
The performance of LED Lighting is not affected much by switching the
power on and off.
To extend the LED's life, utilize the on/off function controlled by external
signals powered by this company, and only turn the LED on when
necessary.
Monochrome
Image
Differences in observation light due to the relative
positions of the Lighting, camera and object.
Depending on the type of object, positional differences of the Lighting,
camera and object can affect the image.
Each situation is described below:
Observing mirror-reflected light
(bright field)
Observing scatter reflection light
(dark field)
Lighting
Lighting
Camera
Observing specular transmission light
(bright field)
Lighting
Observing scatter transmission light
(dark field)
● Use lights at low volumes.
If the light is set to a low volume, the current flowing into the LED
decreases and the heat generation is suppressed.
To choose Lighting with sufficient brightness, evaluate each Lighting when
the camera's aperture is as open as possible.
If using the Lighting continuously, we recommend a volume of 50%.
(Even if performance deteriorates and illuminance is reduced, normal use
can be restored by increasing the volume.)
Lighting
3. Use the Lighting as close as possible to the target object.
Object
Transparent glass
Object
Since the element itself is small, LEDs can manufactured as small and
lightweight lights. The illumninance is inversely proportionate to the square
of the distance, and thus using the Lighting at a close distance can increase
the light intensity greatly.
Clouded glass
Dimensions of virtual light emitting
surface: b
Notes for use
・ Do not look at the source of light directly.
・ Do not disassemble or reconstruct the light or power supply.
・ Do not touch a product under operation with wet hands.
・ Do not use in a high-temperature or high-humidity environment.
・ Avoid installing in a dusty place.
・ Please use following the recommended guidelines concerning heat generation.
・ Please do not use a power supply other than the one provided.
・ The AC power supply should have a different power supply from the mo- tive power, electromagnetic valve etc.
・ A power supply with an earth terminal should be grounded.
・ When installing Lighting, follow all instructions carefully.
※ Please note that the specifications of our products are subject to change without prior notice.
Camera
Warranty
Object
Mirror
The camera and Lighting are on the same side of
the mirror, and it is the same as looking directly at
the Lighting. Only the direction of the light is
different, and the reflected light is captured by the
camera. The reflected light and the camera are
along the same axis. Evenness rather than
brightness is required of the reflected light.
Irregularities on the surface and areas of low
reflectance are comparatively dark.
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Object
White paper
The camera captures images of a part of scattered
light reflected off the surface. Light is reflected in
every direction so the camera's observation axis is
not restricted. Since only a part of the light can be
captured, brightness rather than evenness is
required. Irregularities on the surface and areas of
high reflectance are comparatively bright.
Camera
The camera and Lighting are on opposite sides of
the glass, and it is the same as looking directly at
the Lighting. The camera is aligned with the
direction of the light, and the reflected light is
captured by the camera. The transmitted light and
the camera are along the same axis. Evenness
rather than brightness is required of the reflected
light. Irregularities on the surface and areas of low
reflectance are comparatively dark.
Camera
The camera captues images of a part of scattered
light transmitted from the surface. Light is
reflected in every direction so the camera's
observation axis is not restricted. Since only a part
of the light can be captured, brightness rather than
evenness is required. Irregularities on the surface
and areas of high reflectance are comparatively
bright.
●Period of Warranty : The warranty period of this device is one year from delivery.
●The manufacturer will repair or replace the device free of charge.if a malfunction occurs where the manuafacturer is liable, during the warranty period.
However,malfunctions caused by the following shall be excluded from the manufacturer's warranty.
1.Damage caused by abuse, misuse, or misapplication
2.Damage where the cause is not the delivered product
3.Damage caused by an unapproved modification or repair.
4.Damage due to natural or other disasters
5.Damage caused by use which exceeds standard product use
6.Damage caused by failure to adhere to guidelines or warnings
The warranty stated herein shall cover only the delivered product.
Damage or injury sustained due to a malfunction to this product is not covered by this warranty.
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