Reasons for excessive lumen attenuation of LED lighting products

At the thermal management and reliability technology branch in November 11, 2013, lu Guangjun, R & D engineer from the State Key Laboratory of semiconductor lighting joint innovation, made a report entitled 'analysis on the causes of excessive lumen attenuation of indoor LED lighting products measured by CSA020 method. LV Guangjun said: Compared with traditional lighting products, LED products as the third generation of lighting have many advantages such as energy saving, environmental protection, long service life, safety, good appearance plasticity, flexible driving and easy miniaturization. LED industry is in line with the current policies of energy conservation and environmental protection and building a green and low-carbon life advocated by various countries, so it has received strong support from governments of various countries, especially applications related to public utilities (Such as LED street lamps, etc)It is developing rapidly. However, due to the constraints of cost and other factors, it will take time to completely replace traditional lighting for civilian use. Due to fierce market competition, rapid product upgrading and shortening of development time, it has become an urgent need for the industry. Therefore, the National Semiconductor Lighting Engineering Research and Development and Industry Alliance standardization committee (CSAS) The Alliance standard CSA020 'accelerated attenuation Test Method for LED lighting products' formulated and issued is mainly applicable to LED lighting products such as LED street lamps, LED tunnel lamps, LED spotlights, LED downlights and LED bulb lamps. First of all, the acceleration principle of CSA020 acceleration attenuation test method is that on the premise that the accuracy of the test equipment is guaranteed, it is assumed that the optical pass maintenance rate has an e exponential attenuation relationship with time, the 3600-hour luminous flux attenuation data can be used instead of the 6000-hour data required by the ES test method. In addition, the accelerated attenuation test method uses Arrhenius accelerated model, which has been proved feasible by measured data for many times, to describe the life of LED products at high junction temperature. Therefore, the method uses the ambient temperature (Used to increase LED junction temperature)Further shorten the test time. Under the test condition that the recommended high temperature is 55℃, the data within 2000 hours can be used to replace the data of 6000 hours at room temperature required by ES method. For LED lighting products with high standard working temperature less than 55℃, the high standard working temperature of the products is required to be the high test temperature. The feasibility and rationality of the accelerated attenuation test method adopted in this standard are not only proved in theory, but also verified by actual test data of LED lighting lamps. Secondly, the inspection process proposed by CSA020 standard adopts sampling method, that is to say, the composition of inspection batches: adopt the same materials, components and light sources, and have the same structural form, products continuously produced on the same production line form inspection batches. Inspection samples shall be randomly selected from at least two manufacturing batches. The luminous flux of the sample shall conform to stable attenuation. For sample samples, in the selection of accelerated test temperature, the test chamber is set to the 4 test temperatures listed in Table 1 in sequence, and each test temperature is kept for at least 60 minutes, make the sample reach a stable state of heat balance, and measure the optical properties of the sample at this temperature (Such as illuminance). After each measurement, the sample shall be taken out of the temperature test chamber and allowed to stand at room temperature. When the sample reaches a stable state of thermal equilibrium, the luminous flux shall be measured. The difference between the luminous flux measured by the sample outside the temperature test chamber should be within 5, and the difference between the optical properties measured at the four set test temperatures in the temperature test chamber should be within 10, the test temperature (Except 25 ° C) Reduce 5℃ as the accelerated test temperature for accelerated attenuation test. In the accelerated test, a high accelerated test temperature meeting the above conditions shall be adopted, but shall not be higher than 55℃, and shall not be higher than the nominal high working temperature of the product. Then the accelerated test is carried out, and the sample needs to measure the initial luminous flux first. The sample is then placed in a test chamber for accelerated testing. The test environment temperature is the accelerated test temperature determined above, the relative humidity of the Test environment is not more than 65, and the sample works continuously under the rated voltage. It is concluded that the accelerated test reaches the standard: CSA lists the standard determination methods for samples with nominal life of 25000 hours, 30000 hours and 35000 hours respectively. For the sample whose nominal life is 35000 hours, at a certain accelerating temperature, after all the samples reach the cumulative load time shown in Table 2, the accelerated light pass maintenance rate is not less than 95, then determine the small life expectancy of the sample to reach its nominal life of 35000 hours. If the accelerated temperature is 55℃, the test time required to determine the life of LED lighting products to be 35000 hours, 30000 hours and 25000 hours is only 1750 hours, 1550 hours and 1300 hours respectively. Later, in order to verify that CSA020 'accelerated attenuation Test Method for LED lighting products' is widely representative, 17 representative LED lighting products were selected from downlights, spotlights, bulb lamps, street lamps and tunnel lamps for verification tests. Accelerated at 55℃ and room temperature (25 ° C) Test and verify that the results of the accelerated attenuation test are consistent with the results of the room temperature test. Compared with the US Energy Star ES method, CSA020 'accelerated attenuation Test Method for LED lighting products' can effectively shorten the test time required to predict the life of LED lighting products. The correctness and extensive representativeness of CSA020 test method theory have been verified by a large number of detailed data. Considering the accuracy of the measurement system, using this method can shorten the test time to less than 2000 hours at the test temperature of 55℃. At present, CSA020 is being accepted by dozens of member units of the National Semiconductor Lighting Engineering Research and Development and Industry Alliance. It is believed that it will be recognized by more and more enterprises in the near future, it will definitely play a huge role in promoting the research and development of LED lighting products and industrial development. The number of sample samples is at least 3. The larger the number of samples, the higher the confidence of the test results.