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What is LM-79?



LM-79 is a standard that defines how the performance of an LED lamp or fixture should be measured. A test according to LM-79 is carried out at a point in time and at a single temperature. Therefore, it gives no indication as to how the performance of the device under test (DUT) might change over time or how it might be affected by different ambient temperatures.

The full name of the latest version of this standard is “IES LM-79-19 Approved Method: Optical and Electrical Measurements of Solid State Lighting Products”.

M-79 was written and is published by the Illuminating Engineering Society of North America. It only applies to solid state (ie LED) lighting products and cannot be used for light fittings with other light sources, such as fluorescent, incandescent or high intensity discharge lamps.


LM-79 is important to lighting designers, specifiers and manufacturers. It provides a standard method of testing LED lamps and fixtures so that the data from different brands and models can be directly and objectively compared.

LM-79 is concerned with measuring two groups of LED lamp & luminaire characteristics:

Electrical Measurements.

The electrical data that should be recorded in any LM-79 compliant test will include:

  • RMS AC voltage

  • RMS AC current

  • AC active power

  • Power factor

  • Total harmonic current distortion

  • Voltage frequency

Optical Measurements.

The optical data gathered during a photometric test compliant with LM-79 will typically include the following:

  • Total luminous flux (lumens, lm)

  • Luminous efficacy (lumens/watt, lm/W)

  • Luminous intensity in one or more directions (candelas, cd)

  • Chromaticity coordinates

  • Correlated colour temperature (kelvin, K)

  • Colour rendering index (rendering average, Ra)

Other data such as radiant intensity or photon flux might also be gathered if required by the sponsor of the test.