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LED Tests: LM-79, LM-80&TM-21

Here makes one general introduction to three important electrical and photometric measurements of SSL products, including LM-79, LM-80 and TM-21.

Test for SSL Products



IESLM-79 is one approved method that describes procedures and precautions in performing measurement of LED products.


LM-79 is applied to solid-state lighting products that include the following requirements:

---LED-based products that are integrated control circuit and heat sinks

---LED-based products only requiring AC or DC power supply

And does not cover as bellow:

---LED products requiring external operating circuits or heat sinks (bare LED chips, package and modules)

---Fixtures designed for LED products but sold without a light source

Test Data:

Photometric Requirements:

---Total Luminous Flux

---Electrical Power


---Light Intensity Distribution




Electrical Requirements:

---SSL products work with AC power: voltage, electrical current, power, frequency, power factor

---SSL products work with DC power: voltage, electrical current, power

Test Condition&Procedures:

1. Ambient Conditions

Temperature--maintaining at 25℃±1℃

Air Flow--limited

Mounting--limited thermal transfer

2. Power Supply

Voltage regulation to ±2%

Voltage waveform (harmonic distortion< 3%)

3. Aging and Stabilization

---New SSL products can be put into tested without aging.

---Before testing, SSL products should work for a certain time to reach up stable working temperature.

4. Working Orientation

5. Instrumentation

Test Method:

Integrating Sphere &Goniophotometer available to achieve the test report

LM-79 Test Methods

Integrating Sphere:

For measuring total luminous flux and color

Photometer – Total Luminous Flux

Spectral Radiometer (preferred) - Spectral Radiant

Flux (to derive total luminous flux and color qualities)

IES LM-79 Test Results


For measuring luminous intensity distribution

Total luminous flux is derived

Provides color characteristics with spectral radiometer including CCT, CRI


Before discussing about IES LM-80, I would like to introduce two concepts: life of lamp vs life LEDs.

1. Life of Lamp

When talking about life of lamp, we mean the operation time of lamp(s). For one piece of lamp, while most light sources burn out and the lamp has ended its life. That is operational failure.Typically, lamp life is rated at 50% failure rate.

Life of Lamp

2. Life of LEDs

Life of LEDs refer to the useful light output, which is referred to lumen maintenance.

Life of LEDs


IES LM-80 is one approved method that measure lumen loss SSL light sources, arrays and module. Note that LM-80 measurement do not cover measurement of luminaires and does not define methods for life estimation.

IES LM-80 for LEDs lumen maintenance measurement

Test Data:

Test report basics cover the following:

---Description of Sources tested

---Ambient conditions (Airflow, temperature, RH etc)

---Case Test point temperature

---Electrical conditions

---Lumen maintenance data

---Observation of failures

---Chromaticity shift over time

---LED monitoring interval

Test Conditions&Procedure

1. Ambient Conditions

Case Temperature measured and maintained

Case Temperature measurement point

Airflow minimized

Operating orientation & space

2. Electrical Setting

Voltage and Current (AC or DC levels)

Voltage waveform (harmonic distortion <3%)

Current regulation

3. Temperatures

4. Testing Intervals

---6000 hours min testing period, 10K preferred

--- Minimum at least every 1000 hours



TM-21 is a technical memorandum being developed by an Illuminating Engineering Society (IES).

It is currently in the IES vote/comment stage and therefore, may change before final publication.

It is one separate estimation method to test long term luminance maintenance, which is one important supplement for LM-80.


---Adopted by organizations/programs as documentation of performance

---Program may define who does calculations( lab, manufacturer or other)

---TM-21 may be requested as part of LM-80 test

---Test lab will need to develop calculation sheet

Notice: TM-21 is under development. Here we do not make further discussion about it.

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