Why a New Testing Standard Is Needed for LEDs

Traditional light sources (incandescent, fluorescent, and high-intensity discharge) are rated for luminous flux according to established test procedures. In contrast, there is no standard procedure for rating the luminous flux of LED devices. LED light output estimates (as reported on manufacturer datasheets) are typically based on a short (<1 second) pulse of power applied to the LED chip, with junction temperature held at 25 degrees C. This is because LED chips must be binned for luminious flux and color during the manufacturing process. To run them longer without a heat sink would damage them. LED manufacturers usually list "minimum" and "typical" luminous flux on their product datasheets. There is no standardization of the test conditions, or the meaning of "typical." Further, there is no standard test procedure for measuring the luminous flux of LED arrays, such as multiple LEDs mounted on a circuit board.

In summary, luminous flux—and by extension, luminous efficacy—must be measured at the luminaire level for two primary reasons: 1) no standard procedures are available for rating LED devices on their own, and 2) the amount of light emitted by a fixture cannot be predicted reliably based on available information about LED devices and fixtures. The lighting industry has adopted luminaire efficacy as the preferred measure of LED performance, as evident in the development of a new test procedure based on this approach.

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Nceba N Phike
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