In Situ Temperature Measurement Test (ISTMT)

The Illuminating Engineering Society of North America (IESNA) Approved Method for Measuring Lumen Maintenance of LED Light Sources (LM-80-2008) prescribes the measurement of lumen maintenance for LED-based packages, arrays, and modules only and does not entail testing of the entire luminaire. Therefore, because LEDs are incorporated into luminaries with heat sinks, optical elements, power supplies, etc. and then operated in a variety of ambient environments, LM-80 by itself is not a predictor of luminaire lumen maintenance.

To relate the results of the LM-80 test to the luminaire, most lighting programs and industry professionals require verification of LED and power supply temperatures in environments that simulate real-world applications (in situ) with tests that measure the temperature of both the highest temperature LED in the luminaire and the power supply at steady-state thermal equilibrium.

The procedure is called the In Situ Temperature Measurement Test (ISTMT) which follows ANSI/UL 1598-2004 Luminaires or ANSI/UL 153-2005 Portable Luminaires. It includes the addition of two (or more) thermocouples, one for the LED package, array, or module and one for the power supply.

The ISTMT test is currently utilized by many lighting programs including the DesignLights Consortium (DLC), Energy Star, LED Lighting Facts (option), and various other organizations. ITL has a dedicated ISTMT thermal laboratory and is an accredited laboratory for the test programs listed above.

If you would like to know more about the In Situ Temperature Measurement Test please contact us – we would be happy to discuss your lumen maintenance testing needs.