New test method measures LED illumination

FEBRUARY 23, 2009--Scientists Yuqin Zong and Yoshi Ohno, working at the National Institute of Standards and Technology, have created a standard high-power LED measurement method that satisfies the needs of both LED and lighting manufacturers.

FEBRUARY 23, 2009--Scientists Yuqin Zong and Yoshi Ohno, working at the National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA) have created a standard high-power LED measurement method that satisfies the needs of both LED and lighting manufacturers. The NIST method leverages the fact that the optical and electrical characteristics of an LED are interrelated and a function of the LED's junction temperature (the temperature of the semiconductor chip inside the LED, which is normally very difficult to measure).

The researchers' new method entails mounting the LED on a temperature-controlled heat sink set to the desired LED junction temperature between 10 and 100 degrees Celsius. After applying a pulse of electricity through the LED and measuring the voltage flowing across the junction, scientists turn on the DC power to the LED and adjust the temperature of the heat sink to ensure the voltage remains constant.

When measuring the light output of an LED, this approach allows researchers to achieve a junction temperature similar to that found in a commercial lighting fixture. The measurement results can be reproducible regardless of pulse or DC operation, or type of heat sink. For more information, go to: http://www.nist.gov/public_affairs/techbeat/tb2008_1125.htm#led

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