PhotometricMeasurementofLEDLuminaires-Holophane.pdfVIP

White Paper: Photometric Measurement Photometric Measurement of LED Luminaires ? Relative and Absolute Photometry ? Photometry Standard IESNA LM-79-08 ? DOE CALiPER Program Many aspects of traditional photometry are not applicable for evaluating LED products. With conventional sources of the past, the science of photometry sought to completely decouple the characteristics of the and components to meet their needs. The methodology for this type of testing is known as relative photometry. In this method, a lamp is chosen to measure within the photometer at the lamp manufacturer’s and then calibrated to the lamp manufacturer’s published lumen value. In this way, the actual variation of the tested lamp lumens is factored out of the photometric process. The same lamp and ballast are then placed within the luminaire and the distribution of the light is measured. In this way, the photometry is scaled to the rated value of lumens claimed by the lamp supplier. In addition, the photometry can be used for other lamps that share similar characteristics (size, shape, distribution) by simply scaling the lamp lumens accordingly within lighting application analysis programs (such as Visual? ). Decoupling “lamp” from luminaire in an LED product is not practical since the LED performance is so intricately tied to the thermal design of the luminaire. To overcome this issue, the IES (working in conjunction with DOE) developed IESNA LM-79-08 (Electrical and Photometric Measurement of Solid-State Lighting Products), which is a testing method to measure the performance of LED-based luminaires. This method is termed absolute photometry, since the results are actual or “absolute”, not “relative” or scaled to a source that was not actually tested. The limitation of absolute photometry is that it is applicable only for the exact luminaire / light source combination tested. the world of LED lighting is a quantity that gives no meaningful information about the performance of the LED luminiare.