LED product testing
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The North American LM-79 and LM-80 standards have been around for some time and are useful in characterising the performance of LED products. The LM-80 test is a life & temperature limit test for LED modules and is typically performed by the manufacturer.
When you design your luminaire around the LED module, an ISTM (In-situ temperature measurement) test profiles the temperature characteristics inside your luminaire to ensure the LED module is operating optimally. The results of an LM-79 test identify the key performance metrics: photometry, colorimetry and energy efficiency. |
Photometry
Information we provide to you from our laboratory takes many forms: test reports, photometric and spectral data files, charts for presentation, spreadsheets. Traditional communication of results is in the form of electronic test reports, for accredited activities we supply NATA endorsed reports.
Distribution photometry yields a significant mass of data, best represented in a form that is computer readable. We generate photometric data in many formats, a selection being :
Additionally, the charts that appear on our photometric test reports can be issued to you in electronic format for inclusion in your catalogues. You gain the ease of use of electronic reports, in distribution, publishing and archiving while retaining the security of unambiguous traceability. Photometric data is the raw currency of lighting design. We can put your photometric data to work. With many decades of experience in lighting design and the application of lighting in architecture our designers can create pleasing designs whatever your requirements. Photometric results, coupled with electrical measurements, feed into efficacy and energy efficiency calculations. We can help you find the optimal performance characteristics of your luminaire. |
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LM-79 Testing
LM-79 is an approved method by the Illuminating Engineering Society of North America (IESNA),for measuring the electrical and photometric performance of SSL products. The standard covers total flux (light output), electrical power, efficacy, chromaticity, and intensity distribution. The five required metrics on the LED Lighting Facts label come from LM-79 test results.
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ISTM Testing
In-situ temperature measurement tests are an important part of ensuring LED products meet energy efficiency and lifetime expectations.
An LM80 test, typically issued by an LED manufacturer an LED product, primarily yields the reduction of luminous flux for over time at a given temperature measured at the Temperature Measurement Point (TMP) of the LED. The ISTM test measures the operating temperature and drive current of the LEDs inside the luminaire as would be encountered when the luminaire is operated normally. The Standard prescribing the luminaire conditions during the ISTM test is 60598. Assuming that the TMP temperature and drive current measured in-situ in the luminaire are within the bounds of the LM80 report, the TM21 standard can be used to estimate the expected lifetime of the luminaire. |
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LM-80 & TM21 Calculations:The North American IES standard LM80 prescribes a test method whereby a batch of LEDs are mounted onto a carrier and are tested at a specific drive current and ambient temperature. At intervals during this test the luminous flux, CCT and other metrics are measured. Three ambient temperatures are used in the test: 55°C, 85°C and a temperature chosen by the LED manufacturer. The samples are operated at these temperatures and at a specific drive current for a period of 1000hrs, then the LEDs are removed from the oven, allowed to cool to 25°C ambient and their light output characteristics are measured as per the LED manufacture's specified method; typically by energising the LED for a short interval between 10 and 20 ms. The LEDs are then placed back in the oven and the process repeated for a minimum of 6000hrs (approximately nine months).
Once the LM80 test has concluded, the measurements are used to determine a depreciation curve for the luminous flux at each temperature. The data is extrapolated using the method described in the North American Technical Memorandum TM21 to determine the "Lumen Maintenance Life Projection (Lp)". The end point of the extrapolation is typically 70% of the initial light output. There is a spreadsheet calculator available at the EnergyStar website to perform the calculations. |
