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Photometer Measures Automotive Lighting and Reflectors

Photonics Spectra
May 2000
Daniel C. McCarthy

Standards for automotive retro-reflectors -- as well as signals and forward lighting -- require that these safety components emit or reflect light at specific intensities and angles. In the past, this meant using handheld photometers to obtain flux measurements at different angles to the reflector. Besides requiring ladders to obtain high-angle measurements, the accuracy of this method had limited repeatability in providing positional measurements.

Instead of moving the photometer, goniometers such as those developed by Illumivations Inc. move the light source to deliver accuracy exceeding 0.01°. The detector in the company's goniophotometer system is a research-grade photometer from International Light Inc.

To test a reflector, technicians mount the component on a goniometer at the end of a dark tunnel. From the other end of the tunnel, a projector illuminates the reflector, photodetectors measure the ratio of reflected to projected light, and the goniometer automatically repositions the reflector for measurement at another angle. 

Illumivations' more advanced systems actually integrate three photodetectors. Two detectors affixed directly above the projector measure reflectance. A third detector at the goniometer end of the tunnel measures projector output. By making one of the detectors movable, the systems can provide for both the 0.2° and 0.333° observation angles required by US and European reflector standards.

"Within a couple minutes you have tested all 20 or 30 test points," said Mark Mayer, president of Illumivations. "It takes longer to mount the light to the goniometer than it does to run a complete test."

"International Light's photodetectors and radiometers offered high quality and low cost," he said of his selection. This equipment helped his company to manufacture a system that can sell for less than half the price of its nearest competitor. But the detector's wide dynamic range and simplified computer output also played a role.

"It has wide dynamic range -- a measure of intensity -- from 0.5 millilux up to a million lux," said Bob Angelo, vice president of sales for International Light. "That's 10 decades of range compared to the 3.5 decades found in handheld photometers."

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