LED lighting products lumens decay too fast


At the Thermal Management and Reliability Technology Branch on November 11, 2013, Lu Guangjun, a research and development engineer from the National Key Laboratory of Semiconductor Lighting Innovation, gave an analysis of the causes of the lumen degradation of indoor LED lighting products measured by the CSA020 method. report.
Lu Guangjun said: Compared with traditional lighting products, LED products as the third generation of lighting have many advantages such as energy saving, long life, safety, good appearance plasticity, flexible driving and easy size and miniaturization. The LED industry is in line with the policies advocated by countries for energy conservation and environmental protection and green and low-carbon life. Therefore, it has received strong support from governments, especially utilities-related applications (such as LED street lights). However, due to cost and other factors, it will take time to completely replace traditional lighting in civilian use. Due to fierce market competition, rapid product upgrades, and shortened development time, it has become an urgent need of the industry.
Therefore, the National Semiconductor Lighting Engineering R&D and Industry Alliance Standardization Committee (CSAS) has developed the alliance standard CSA020 "LED Lighting Product Acceleration Attenuation Test Method", which is mainly applicable to LED street lights, LED tunnel lights, LED spot lights, LED downlights and LED balls. LED lighting products such as bulbs.
First, the acceleration principle of the CSA020 accelerated decay test method is that, under the premise that the accuracy of the test equipment is guaranteed, assuming that the lumen maintenance rate and the time are exponentially decaying, the 3600 hours of luminous flux attenuation data can be used instead of the ES test method. 6000 hours of data. In addition, the accelerated decay test method uses a number of Arrhenius acceleration models that have been validated by measured data to describe the lifetime of LED products at high junction temperatures. Therefore, the method further reduces the test time by increasing the ambient temperature at the time of testing (to increase the junction temperature of the LED). Under the recommended test conditions of a maximum temperature of 55 ° C, data within 2000 hours can be used to replace the 6000 hours of data at room temperature required by the ES method. For LED lighting products with a maximum nominal operating temperature of less than 55 ° C, the highest nominal operating temperature of the product is required to be the highest test temperature. The feasibility and rationality of the accelerated attenuation test method adopted by this standard are not only proved theoretically, but also verified by the actual test data of LED lighting fixtures.
Secondly, the inspection process proposed by the CSA020 standard adopts the sampling method, that is to say the inspection batch composition: the same material, components and light source, and the same structure form, the product batch inspection batch produced continuously on the same production line Times. Test samples should be randomly selected from at least two manufacturing lots. The luminous flux of the sample should conform to a stable attenuation.
For the selection of the accelerated test temperature, the test chambers are set to the four test temperatures listed in Table 1 and maintained at each test temperature for at least 60 minutes to bring the sample to a thermal equilibrium steady state. The sample is measured at this temperature. Optical properties (such as illuminance). At the end of each measurement, the sample should be removed from the temperature chamber and allowed to stand at room temperature to measure the luminous flux when the sample reaches a thermal equilibrium steady state.
The difference between the luminous flux measured outside the temperature test chamber shall be within 5, and the difference between the optical properties measured at the four set test temperatures in the temperature test chamber shall be within 10, then The test temperature (except 25 ° C) was reduced by 5 ° C as the accelerated test temperature for the accelerated decay test. The highest accelerated test temperature that satisfies the above conditions shall be used in the accelerated test, but shall not be higher than 55 ° C and shall not be higher than the nominal maximum operating temperature of the product.
An accelerated test is then performed and the sample is first measured for initial luminous flux. The sample was then placed in a test chamber for an accelerated test. The test ambient temperature is the accelerated test temperature determined above, the relative humidity of the test environment does not exceed 65, and the sample is continuously operated at the rated voltage.
The accelerated test compliance test was obtained: CSA listed the method for determining the compliance of samples with nominal lifetimes of 25,000 hours, 30,000 hours, and 35,000 hours. For example, if the sample has a nominal life of 35,000 hours, at a certain acceleration temperature, after all the samples reach the cumulative load time shown in Table 2, the accelerated luminous flux maintenance rate is not less than 95, then the minimum expected life of the sample is determined to reach its nominal value. The life span is 35,000 hours. If the acceleration temperature is 55 ° C, the test time required to determine the LED lighting product life of 35,000 hours, 30,000 hours, and 25,000 hours is only 1750 hours, 1550 hours, and 1300 hours, respectively.
Finally, in order to verify CSA020 "LED lighting products accelerated attenuation test method" has a wide representative, 17 representative LED lighting products selected in downlights, spotlights, bulbs, street lights and tunnel lights for verification test . At 55 ° C acceleration and room temperature (25 ° C) test, the results of the accelerated decay test were verified to be consistent with the room temperature test results. Compared with the US ENERGY STAR ES method, CSA020 "LED Lighting Product Accelerated Attenuation Test Method" can effectively shorten the test time required to predict the life of LED lighting products. The correctness and extensive representation of the CSA020 test method theory has been verified by a large number of detailed data. Taking into account the accuracy of the measurement system, this method can be used to shorten the test time to less than 2000 hours at a test temperature of 55 °C.
At present, CSA020 is being received by dozens of member units of National Semiconductor Lighting Engineering R&D and Industry Alliance. It is believed that more and more companies will be recognized in the near future, which will definitely promote the development and industrial development of LED lighting products. . The number of sample samples is at least 3. The more the number of samples, the higher the confidence of the test results.

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