TESTS FOR LED LUMINAIRES LIFETIME & PERFORMANCE; CORRELATION AMONG LM-79, LM-80, & TM-21 - A BRIEF SUMMARY

Understanding LM-79, LM-80, & TM-21 can help in the evaluation of LED products concerning their performance and lifetime.

End users, like Saudi Aramco, need test reports, as per SAES-P-123, of LED luminaires to ascertain their performance. So, we need to have a clear concept and understanding of these standards and their differences.

IES LM-79-08

I - DESCRIPTION:

Approved Method for Optical and Electrical Measurements of Solid-State Lighting Products.

II - SUMMARY OF STANDARD:

It describes the procedures to be followed and precautions to be observed in performing?reproducible accurate measurements of total luminous, radiant, or photon flux; electrical power;?system efficacy; luminous, radiant, or photon intensity distribution; and colour quantities and/or?spectrum of solid-state lighting (SSL) products for illumination purposes, under standard conditions. This approved method covers LED luminaires, OLED luminaires, integrated LED?lamps, integrated OLED lamps, non-integrated LED lamps operated with a driver designated by a manufacturer’s identification number or by a defined [ANSI] reference circuit, and LED light engines, all of which will be referred to as SSL products or device under test (DUT). SSL products, excluding non-integrated LED lamps, are intended to directly connect to AC mains power or to a DC voltage power supply to operate.

III - SCOPE OF TESTS:

LM-79 measures a luminaire or integral lamp as a system and measures light output (flux), electrical power, chromaticity, efficacy, and intensity distribution using standard processes and equipment.

IV - TESTS CONDUCTED:

Integrating Sphere Test for the lower CCT: Tests for measuring Chromaticity coordinates, ?correlated colour temperature and colour rendering index - Performed by using an integrating sphere, a spectroradiometer and software.

Goniophotometer Test:?Tests for measuring Luminous flux, luminaire efficacy, and zonal lumen - Performed by using a type C goniophotometer and software.

Electrical Characteristics: A variety of electrical measurements may be conducted as part of LM-79 testing, including but not limited to:

*?Input voltage, expressed in volts (V). Testing is performed with the SSL product operated at its rated input voltage.

?*?Input current, expressed in amperes (A). Input current can be either direct current (DC) or alternating current (AC), depending on product design. Note that this metric is not equivalent to the current supplied to a given LED light.

V – FOOTNOTE:

It is the major method to test electrical characteristics, Lumen Output & Luminous Efficacy, and?Spatial Distribution of Light.

The five required metrics (scope of test) are mandatory on LED Lighting Facts labels and come from the results of LM-79 testing.

EN 13032-4:2015, Measurement and presentation of photometric data of lamps and luminaires, ?Part 4 LED lamps, modules, and Luminaires is the equivalent of LM-79.

IES LM-80-15

I - DESCRIPTION:

Approved Method for Measuring Lumens Maintenance of LED Light Source.??(Test Methods for Lifetime of LEDs)

II - SUMMARY OF STANDARD:

LM-80 is the Illuminating Engineering Society of North America (IESNA) approved method for?measuring lumen maintenance of LED light sources like packages, arrays, and modules at different temperatures. This standard does not test a complete system, but rather a component. LM-80 specifies a testing period of 6,000 hours though 10,000 is preferred. The testing also requires 1,000-hour increments. LM-80 doesn’t provide expected life beyond test data.

III - SCOPE OF TESTS:

i. Covers LED packages, arrays and modules only (not LED luminaires). ?

ii. The lifetime of LEDs is strongly dependent on the junction temperature.

iii. The final purpose is to determine the lifetime of Solid-state LED products.

iv. Defines Lumens Maintenance Life.

??????????* L70 (hours): 70% lumen maintenance.

???????????* L50 (hours): 50% lumen maintenance.

v. It doesn't consider the failure rate.

IV - TESTS CONDUCTED:

LED Packages are driven at a constant current for the life test and are pulsed for the photometric test i.e.,?Ageing Test at the LED case Temperatures. There are three types of tests conducted at three different test temperatures i.e., 55°C (TC1), 85°C (TC2), & manufacturer chosen temperature (TC3), which are,

???????????i. Lumen Maintenance Life.

???????????ii. Chromaticity Shift.

???????????ii. Forward Voltage Maintenance.

??(Ambient temperature during lumens and chromaticity measurement shall be 25°C +/- 1°C)

V – FOOTNOTE:

Simply put, LM-80 is the method of measuring the lumen depreciation of LED sources. LM-80?determines the rated life of the LED module, but not the life of the complete LED product. Other components like drivers, electrical connections, product integrity, etc. may fail before the LEDs.

IES TM-21-11

I - DESCRIPTION:

Projects Long-Term Lumen Maintenance of LED Light Source.

II - SUMMARY OF STANDARD:

It is the Illuminating Engineering Society of North America (IESNA) approved method for taking?LM-80 data and making useful LED lifetime projections. The standard applies to the lifetime projection of LED package, array or module alone. The results can then be used to interpolate the lifetime of an LED source within a system (luminaire or integrated lamp) using the in-situ LED source case temperature.

?It provides recommendations for projecting long-term lumen maintenance of LED light sources using data obtained when testing them per IES LM-80-08, “IES Approved Method for Measuring Lumen Maintenance of LED Light Sources.”

III - SCOPE OF TESTS:

i. No Tests are conducted as TM-21 is based on calculations.

ii. TM-21 establishes a standard way to use LM-80 data to make consistent lifetime projections beyond the testing period. TM-21 dictates which values can be used in the calculation based on the sample size, number of hours and intervals tested, and test suite temperature. It also puts a cap on the extrapolation – a maximum of 6X the hours tested – eliminating those infamous 100,000-hour claims of the past. Since most manufacturers test for 6,000 or 10,000 hours, the accurate range based on TM-21 is up to 36,000 to 60,000 hours of useful life. After this period, it does not mean the LED will fail; it is just the limit that can be claimed when using TM-21.

IV - TESTS CONDUCTED:

EPA's Approved ENERGY STAR CALCULATOR can be used to get the projection of lumen maintenance: There are four areas in the calculator as explained below.

?i. TM-21 INPUTS: LM-80 test inputs e.g., source data, sample size, case temperature, drive current, in-situ temperature data, percentage of initial lumens to project to - IN-SITU INPUTS.

?ii. PRODUCT INPUTS: Report at each LM-80 test condition.

?iii. TM-21 PROJECTIONS.

?iv. TM-21 REPORT: L70 at ToC in Hours.

V – FOOTNOTE:

Simply put, the TM-21 standard picks up where the LM-80 left off.

?TM-21 provides guidelines on the use of data compiled through LM-80 tests to assess the lifespan of a light source beyond the number of test hours recommended by LM-80; TM-21 allows us to deduce the lifespan up to six times the number of test hours. For instance, diodes tested for 6,000 hours in a laboratory setting should not be sold with an endorsement stipulating a lifespan greater than 36,000 hours based on the L70 lifespan.