[Source: "High - tech LED - Technology and Applications" November issue ] This paper briefly introduces the development of lumen maintenance life assessment standards for LED light sources in the North American System (IES) and the International Electrotechnical Commission (IEC) system, and maintains the lifetime of the IES TM-21-11 LED light source released by the American Society of Lighting Engineering in 2011. The data selection and data processing methods in the calculation method are questioned. The problematic view is illustrated by the data processing example of the lumen maintenance life of an LED light source in E3.0, which proves the author's point of view. It is expected to provide reference for relevant people in the domestic semiconductor lighting industry.
I. Introduction At present, due to the lack of detection methods and standards, there is no uniform specification for the life evaluation of LED light sources, which leads to uneven products in the LED light source market. In the LED market, LED light source products claiming a life of 50,000 or even 100,000 hours are often seen, but in the use of users, the results are not satisfactory. This situation has greatly hampered users' confidence in LED light source products, thus limiting the healthy development of the entire LED industry.
Due to the complexity and particularity of the LED light source, the lumen maintenance life of the LED light source product has not yet been released by professional organizations in the international industry. It cannot be extrapolated by the test results accelerated in a short time, but needs to be compared. Long-term life testing can be approximated, so the correctness and accuracy of the life assessment method is critical to the assessment.
Second, the development and status quo of LED light source life assessment standards The life evaluation criteria for the slow degradation of LED light sources are mainly typical of the North American System (IES) and the International Electrotechnical Commission (IEC) system. Among them, the IEC system does not advocate the evaluation of the life of the LED light source, but the grading according to the lumen maintenance rate within a limited time, and the temperature of the aging test cannot exceed the maximum ambient temperature used by the light source.
In 2008, the Energy Star certification standard IES LM-80-08 issued by the American Society of Lighting Engineering required the minimum duration of the LED light source lumen maintenance test to be 6000 hours, and the recommended test duration was 10,000 hours. The ENERGY STAR 2011 release of the IES TM-21-11 LED source lumen maintenance life is a supplement to the test results in the IES LM-80-08. In the IES TM-21-11 standard, the fitting estimate for lumen maintenance life of an LED source can only approximate the lifetime of the product.
Third, doubts about the IES TM-21-11 standard The lumen maintenance life of LED light sources is defined in IES TM-21-11, which provides a method for predicting the lumen maintenance life and extrapolating the lumen maintenance life at other service temperatures. However, several statements or algorithms in the text are debatable.
First, IES TM-21-11 pointed out in the text 5.2.3 that the test data within 1000h is not used as the effective data point of the least squares fitting curve of the LED light source. The lumen maintenance life test is between 6000h and 10000h, at least 5000h. Data; greater than 10000h, with the last 50% of the data. Since the lumen degradation rate of LED products is directly related to the operating temperature of the product, there is no basis for the selection of the data processing interval. Moreover, the test interval specified in IES TM-21-11 is every 1000h. Therefore, there are only 6 test data for 5000h duration, and the data change amount is small after the test, which is greatly affected by the operation error of personnel and equipment, resulting in the fitting curve. Deviation, extrapolation lumens maintain life data distortion. Due to the lack of a large amount of experimental data for support, the author believes that the above statement is not rigorous and inadequate.
Second, the Alenis equation in IES TM-21-11 text 6.3 is incorrect. The temperature in the equation should be the junction temperature Tj,i instead of the shell temperature Ts,i. Due to the incorrect parameter values used, the calculated activation energy and the lifetime of the LED source at a certain temperature obtained by extrapolation are not credible. For example, two LED light sources A and B with the same shell temperature and different models have different thermal resistances from the A and B light source chips to the package due to different structures and thermal designs, so that the junction temperatures of the A and B light sources are different. Larger. The degradation rate of the output light flux of the LED light source is positively correlated with the temperature, so the lumen maintenance life of the two light sources is different. If the equations in the paper are used, the lumens of the two sources will maintain the same lifetime.
Unfinished For more information, please refer to "High - tech LED - Technology and Applications" November issue 
July 27, 2023
