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Two methods of testing LED lighting life
The most important feature of LED light source is the long-life, can reach 50,000 to 100,000 hours, long-term monitoring of its light fades situation is not practical, therefore, this standard will predict the lifetime of LED lighting through an accelerated life test method. This standard applies to all types of LED lighting life testing, does not contain the test of the lamp driver. The technical requirements of the LED lamps light output is 70% of the initial light output as a lifetime judge failure indicators. First test method, it is important reason for the junction temperature of the LED light affect attenuation. LED junction temperature rise causes the light fades quickly. LED working at high currents may generate additional heat, which accelerate the aging. This test method uses a different drive currents, selecting five LED lamps at 25 ℃ ambient temperature, with different current accelerated life test, gain the mathematical model of the light output attenuation. Mathematical model y = exp (-αt) α = m × exp (nI) wherein y represents the relative light output, α represents the attenuation constant, t is time of lighting, m, n is a constant, I is the test current. According to the test data on the y and t obtained under different current, final results of the different lighting attenuation coefficient α, so as to arrive at 70% lumen maintenance lifetime value of t70%. Second test method, the temperature as a constant accelerated stress , calculate the life expectancy at 25 ℃ LED lighting failure criterion of 70%. Select five identical specifications of the LED lamps, adjust the oven temperature, respectively, at 50 ℃, 80 ℃, 100 ℃, 120 ℃, 150 ℃ condition, rated current, constant-current condition as a constant acceleration conditions. Recorded 5 set all the parameters during the test of reliability: the light output (light intensity or illumination or luminous flux),
the test time, current, power, the junction temperature etc. Using a mathematical model alendronate Nice P = P0exp (-βt) β = β0IFexp (-Ea / kTj) wherein P0 is the initial light output, P is the time after heating power on light output, β is the attenuation under a certain temperature, t is a power working time under a certain temperature, β0 is a constant, Ea is the activation energy, k is Boltzmann's constant, IF is the operating current, Tj is the junction temperature. • After transformation and test data derived from the formula Ea = [K × In (t2 / t1)] / (1 / Tj2-1 / Tj1) t2 = t1 × exp [Ea / K (1 / Tj2-1 / Tj1) thereby failure judgment obtained at 25 ℃ life expectancy of 70%.
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