Product Selection Guide Page 1113 Product Selection Guide-11th Edition

Additional background on LM-79-08: A word of caution is warranted here. With the emergence of this standard, there may be a false sense of confidence that the photometric data reported is representative of a population of luminaires. With regard to the use of photometric data, LM-79-08 states "The data, however, should be used with the understanding that the photometric file describes the performance of a single luminaire and does not necessarily represent the average performance of a group of the same SSL luminaires." As LED luminaires have become more integrated, optically and thermally, with the LED light source, it is now the responsibility of the luminaire manufacturer to ensure that their published photometric performance data is indeed representative of the range of LED bins (lumens, color and voltage) they have selected for each product. In the past this was less of a concern as major manufacturers of conventional lamps maintained control of their product performance, luminaire design had far less impact on lamp performance, and luminaire manufacturers simply controlled the optical performance of their fixtures. To address this issue, the U.S. Department of Energy has established an LED product integrity program known as CALiPER1 to test products and audit manufacturer's published performance data. Thus far the program has shown product integrity to be a valid concern as there have been numerous instances where manufacturers' claims could not be validated by the CALiPER labs. 1 1 CALiPER stands for Commercially Available LED Product Evaluation and Reporting. It is a program administered by the U.S. Department of Energy that supports testing of LED lighting products for non-commercial and educational use. For more information on the program, refer to: about_caliper.html. 1113 PRODUCT INFORMATION Photometric Measurements LED TECHNICAL INFORMATION PSG11 TECHNICAL INFORMATION Relative Photometry Bare-Lamp Lumens =1000 Delivered Fixture Luminaire Lumens = 700 Efficiency = 70% Absolute Photometry Bare-Lamp Lumens=1000 Delivered Fixture Luminaire Lumens = 700 Efficiency = 100% How is a Luminaire 100% Efficient? In traditional relative photometry, luminaire efficiency is a ratio of the amount of light exiting the luminaire to the amount of light being produced by the lamps within. When light interacts with materials it can be reflected, transmitted or absorbed. Luminaire efficiency is essentially an inverse measure of the net absorption that takes place within a luminaire optical system. Higher efficiency indicates less absorption and is expressed as more lumens exiting the luminaire. With the absolute photometry method, as prescribed in LM-79-08, there is no measurement taken of the bare LED "lamp" since it cannot be removed from the luminaire without significantly altering its performance characteristics. This precludes the ability to ratio the light exiting the luminaire relative to the light produced only by the "lamp" - or in this case the LED module. Since the only quantity that is measured is the luminaire lumens, the efficiency of LED luminiares is by default 100%.

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