Methods for measuring LED modules (LM80, LM79, LM70, LM21)

Methods for measuring LED modules (LM80, LM79, LM70, LM21)

July 30, 2019

We have got this questions a lot from our customers regularly, and it’s easy to confuse LM80, LM79 and L70 or assume they test the same measure in an LED product. Although all of them are used when discussing LEDs, they are not related measurements.

Understanding LM-79,LM-80, L70 can help you evaluate LED products. Learn why LM-80 matters and how the data can be used to improve your bottom line. So what are the differences of them? This post will give you detailed explanation.

What is LM80?

LM-80 refers to a method for measuring the lumen depreciation of solid‐state light sources, such as LED packages, modules and arrays. Before the advent of LM-80, LED component manufacturers each reported lumen maintenance data using their own disparate and varied systems.

To avoid customer confusion, members of the Illuminating Engineering Society (IES), came together to create a standard methodology that would allow customers to evaluate and compare the lumen maintenance of LED components from different companies. LM-80 was born.

    • It was developed by the Illuminating Engineering Society of North America (IESNA), to allow people the ability to evaluate and compare the lumen maintenance of LED components from different companies.
    • It is typically a 6000hr test (can be 10,000hrs) that shows depreciation and chromaticity shift over the period at particular operating temperatures 55 degrees, 85 degrees and a third manufacturer defined temperature, say 105 degrees.
    Who can perform testing?

    LM-80 testing should be performed by EPA recognized Laboratories. Only reports from recognized laboratories are relevant. This standard is used for Department Of Energy (DOE) ENERGY STAR program early qualification in conjunction with other reports.

    What does it provide?

    The testing report issued according to a standard format will provide luminous flux for a given current over a 6,000 hours period with interval measurements. Luminous flux will be measure for 3 different LED case temperatures: 55ºC, 85ºC and a third temperature to be selected by manufacturer. Besides, the lumen maintenance, the chromaticity shifts over the measured period.

    Typically, LED chips are tested for 6,000 hours and extrapolated until they reach L70. LM-80 determines the rated life of the LED module, but not the life of the complete LED product. Other components, such as drivers, electrical connections, product integrity, etc. may fail before the LEDs.

    What is TM-21?

    LM-21 is the Illuminating Engineering Society of North America (IESNA) approved method for taking LM-80 data and making useful LED lifetime projections. The standards apply to 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.

    Who can perform testing?

    There is not such a thing as testing, it is a mathematical method based on LM-80-08 collected data. Among other thing, TM-21-11 will consider:

    • If total LM-80 data period is between 6,000 and 10,000 hrs, we consider the last 5,000 hours
    • If total data period is above 10,000 hours, we use the last half of collected data
    • In situ case temperature interpolation using Arrhenius equation between LM-80 temperature
    • Projections are limited to 6 times the available LM-80 data period so projected and reported lifetime may or not be the same

    For example, at LEDtroniks we test several of our popular downlight products for 10,000 hours or longer, so that we can claim a 50,000-hour-or-more lifetime for our products.

    What is LM79?

    LM79 is the Illuminating Engineering Society of North America (IESNA) approved method for the Electrical and Photometric Measurements of Solid-State Lighting. It measures an LED luminaire or integral lamp as a whole system according to a standard process using IES and integrating sphere equipment.

    Who can perform testing?

    LM-79-08 testing should be performed by EPA-Recognized Laboratories for the category of product tested. Only reports from recognized laboratories are relevant. This standard is used for Department Of Energy (DOE) ENERGY STAR program qualification and lighting facts advocate program.

    What does it provide?

    The testing report issued according to a standard format will provide:

    • Total Luminous Flux (light output)
    • Luminous Intensity Distribution
    • Electrical Power Characteristics (wattage, voltage…)
    • Luminous Efficacy (calculated)
    • Color Characteristics (CRI, CCT…)

    While LM79 measures several aspects of a complete fixture, LM-80 solely measures the lumen depreciation of the LED module.

    What does it provide?

    The method will provide a projected lifetime for the LED source or system. Life notation results will then use the following standardized nomenclature: Lp (Yk)

    • P: Lumen maintenance percentage. For LED luminaire we consider L70 to be the standard. After 30% lumen depreciation, we consider the system is not performing its duty anymore and should be replaced.
    • Y: Length of LM-80 data period in thousands of hours.
      Example: L70(6k) = 36,000 hours

    What is LM70

    “My LED’s will last for 50,000 hours.” “My LED’s will last for 100,000 hours.” We have all heard these claims. The truth is that an LED being an electronic device with no moving parts could theoretically last forever.

    Three things can kill a LED. Heat, dirty power and moisture will all have detrimental eff ects on LED life. In reality, even if LED’s could last forever, their lumen output will diminish over time to a point where they would no longer function as a useful lighting source. We call this “lumen maintenance.” The industry has determined that the LED ceases to be a useful light source when lumen output reduces to 70% of its initial lumens. This is called L70.

    L70 is a lifetime measurement criteria developed by IESNA (Illuminating Engineering Society of North America) to evaluate the useful lifetime of an LED luminaire in terms of the expected number of operating hours until the light output has diminished to 70% of initial levels. or when the lumen output is 70% of its initial output.

    As LEDs do not fail and “burn out” like other light sources; instead, they gradually decrease over time until they are no longer producing useful light. It is generally established that the human eye is only sensitive to lumen depreciation of 30% or more. Therefore, L70 lifetime is defined by Illuminating Engineering Society Standard LM-80-08, entitled “IES Approved Method for Measuring Lumen Maintenance of LED Light Sources.

    L70 lifetime is dependent upon many variables, such as the operating temperature, drive current, and the technology and materials used to construct the products.

    LEDtroniks products and components are sourced only from recognized suppliers that are able to offer full reports for their products, if you need more information, please get in touch.

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