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Determining spectral efficiency of light source

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Determining spectral efficiency of light source

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Determining spectral efficiency of light source

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See before: What is spectral efficiency.

 

Problem

 

There is a lamp and a camera. It is necessary to measure spectral efficiency of this lamp for this camera in relation to the halogen incandescent lamp.

 

Equipment:

 

To perform the measurements you need the software CCTVCAD Lab Toolkit (visit http://cctvcad.com ).

 

•Luxmeter (a device for measuring illumination). Almost any kind of such a device with standard CIE spectral response will suit.
•Any PC-based video capture system, TV-tuner with video input, etc. The System should allow to display live video on the computer screen.
•Video Analyzer utility. It is a part of CCTVCAD Lab Toolkit.
•Tungsten halogen lamp of approximately the same power consumption, as testing lamp.
•Manual iris lens, focal length 4-8mm.
• Stand. It is recommended for convenience and accuracy.

 

Measuring should be performed in a dark room.

 

Order of work

 

1. Switch off all image processing options and AGC in the camera.

AGC switching off increases accuracy and allows working with illumination of 5..10lx, even if the camera has sensitivity of 0.2..1lx.

 

2. Mount the manual iris lens on the camera, mount the camera on stand, direct it towards sheet of paper, connect to computer, display image on the screen.

 

3. On the sheet of paper, in the camera field-of-view place the luxmeter sensor.

 

4. Close to the sensor window directly on the sensor, fix a small piece of even white paper.

 

5. Run Video Analyzer. Mark Cycle box, click Start. After that move fast the mouse cursor to the small piece of even white paper on the screen, close to the sensor window.

 

6. Switch off common light. Switch on the testing lamp and fix it at a middle distance from luxmeter sensor.

 

There should be a possibility to approach and move away the lamp.

 

Be sure, that the luxmeter sensor window and the small piece of paper on the sensor have visually equal illumination.

 

7. By adjusting aperture, obtain that the Average brightness measured by the Video analyzer would be equal to 0.22-0.25 after finishing measuring cycle by 100 frames.

 

The objects on the image should be recognized.

 

You must not change the lamp supply voltage. It should be equal to nominal lamp supply voltage. Change Illumination only be means of distance variation between the lamp and the sheet of paper.

 

8. Write down luxmeter reading and the Average brightness value according to the Video analyzer reading.

 

9. Switch off the testing lamp. Switch on the halogen lamp.

 

10. By changing the distance from the lamp to the sheet of paper, obtain equal with step 8 value of Average brightness after finishing measuring cycle by 100 frames.

 

You must not change the lamp supply voltage. It should be equal to nominal lamp supply voltage. Change Illumination only be means of distance variation between the lamp and the sheet of paper.

Be sure, that the luxmeter sensor window and the small piece of paper on the sensor have visually equal illumination.

 

11. Write down the luxmeter reading.

 

12. Spectral efficiency factor of the tested lamp=illumination from tungsten halogen lamp (step11)/illumination from the tested lamp (step 8).

 

You can insert the obtained factor in the Illuminator calculation box.

 

See also: What is spectral efficiency.