How to predict the life of LED?
The life expectancy is a universal and urgent requirement in the LED industry. The half-life of LEDs is usually the time when the luminous intensity or luminous flux decays to 50% of the initial value. For the prediction of the life of LEDs, IEC has held several light source expert meetings to raise the temperature. Carry out an accelerated life test. Generally, life prediction tests are divided into two categories.
One, one of the LED life test methods
(1) Long-term life test. In order to confirm whether the life of the LED lamp reaches 35,000 hours, according to the regulations of the American ASSIST Alliance, a long-term life test should be carried out. First, it needs to be electrically aged for 1000 hours, and then the luminous flux is measured as the initial value. Then add the rated current and energize for 3000h, the measured luminous flux should attenuate less than 4%, and then continue to energize for 3000h, the luminous flux attenuation should be less than 8%, and then energize for 4000h, the measured luminous flux attenuation should be less than 14% of the initial value, so after the luminous flux is measured A total of 11,000 hours were energized, and the luminous flux reached more than 86% of the initial value. At this time, it can be proved to ensure that the life of the LED reaches 35,000 hours. This method is more troublesome. 11,000 h means more than one year of experimentation, which is really of little practical significance.
Two, led life test method two
(2) Accelerated life test. The accelerated life test of electronic devices can be carried out under increased stress (the stress here is not the mechanical stress, but refers to the corresponding experimental conditions). The method to be discussed here is the use of temperature stress, and the measured and calculated life is the average LED Life, namely MTTF. "Information Technology and Standardization" magazine proposed this method. Using this method will greatly shorten the test time of LED life, which is beneficial to timely improvement and improvement of LED reliability. The life test method of increasing the temperature stress has been mentioned in many materials, mainly by quoting the "yamakoshi" (yamakoshi) light-emitting tube light power slow degradation formula, through the degradation coefficient to obtain the life test of the LED under different accelerated stress temperatures Data, and then use the numerical analysis method of the "Arrhenius" equation to obtain the average life of the LED under normal stress, referred to as the "degradation coefficient analysis method", which uses three different stress temperatures, namely 165, 175, and 185℃ Next, the measured data calculates the consistency of the average lifespan at room temperature. The test method is reliable. It is based on the accelerated life test method of electronic components specified in the national standard (GB1772), and the working environment temperature is selected as the accelerated stress. At present, relevant units have drafted and formulated the "Test Methods for the Life of Semiconductor Light-Emitting Diodes" standard, and some domestic enterprises have also developed equipment and instruments for accelerated life testing at the same time. This promotes the development of the LED industry. In addition to using temperature stress, current stress can also be used to perform accelerated life tests on high-power LEDs, using 1.5 times the current, or applying temperature stress, which can be a comprehensive attempt.
3. What is the result?
Currently used LED street lights, such as the manufacturer's accelerated aging test, and the national testing agency's test and calculation of the 5000h light attenuation rate is less than 3%, it is inferred that the light attenuation to 70% needs 50,000h. This data has been proven in more than a year of practice, and the LED lights that pass the test should be safe to use as road lighting.
