A Comparison of LM-85 LED Measurement Techniques

The IES LM-85 testing standard documents three different methods for LED photometric measurements. All three methods use the LED junction temperature as a key reference measurement. When this reference was chosen, LM-85’s authors thought it would ensure that all three methods would produce equivalent measurements. In practice though, other factors, such as phosphor temperature and current pulse shape, also influence the measurement. This paper presents the status of research conducted jointly by Vektrex and Lumileds to explore LM-85 measurement differences and what causes them. In the research Vektrex tested phosphor and non-phosphor LEDs using the three methods. A precision pulsed current source/measure unit, a precision temperature platform, and a spectrometer were used in the testing. These instruments can accurately measure 0.05% flux differences. The resulting preliminary data shows that the methods are often equivalent, but not always so. It also exposes a new error source that is seems to be specific to AlInGaP LEDs. This talk will provide an overview of the research, the methodology, and the quantitative findings.

If you’re interested in this presentation, please contact Vektrex for more information.