Introduce two LED lamp life test methods

• The biggest characteristic of LED light source is long life, which can reach 50,000~100000 hours. It is not practical to monitor the light decay condition for a long time. Therefore, this standard will predict the life of LED lamps through an accelerated life test method.

Scope of application

• This standard applies to the life test of various types of LED lamps, and does not include the test of the power supply part of the lamps.

skills requirement

• The light output of the LED luminaire is 70% of the initial light output as an indicator of life failure.

Test method one

• Junction temperature is an important cause of LED light attenuation. An increase in junction temperature can cause LED light to decay quickly. LEDs operating at high currents generate more heat and accelerate aging.

• This test method uses different driving currents, select 5 LED lamps, and use the different currents for accelerated life test at 25 °C ambient temperature to obtain a mathematical model of light output attenuation.

• mathematical model

y=exp(-αt)

α=m×exp(nI)

Where y represents the relative light output, α represents the decay constant, t is the lighting time, m and n are constants, and I is the test current.

• According to the test data about y and t obtained under different currents, the attenuation coefficient α of different lamps is finally obtained, and the lifetime value of the luminous flux maintenance rate at 70% is obtained.

Test method two

• Using temperature as a constant acceleration stress, calculate the expected life at 70% of the LED lamp failure criteria at 25 °C.

• Select 5 LED lamps of the same specification and adjust the temperature of the oven at 50 °C, 80 °C, 100 °C, 120 °C, 150 °C, respectively, under the condition of constant current and constant current as constant acceleration conditions.

• Record all parameters of the 5 sets of LED test procedures: light output (illuminance or light intensity or luminous flux), test time, current, power, junction temperature, etc.

• Using the Alannis mathematical model

P=P0exp(-βt)

β=β0IFexp(-Ea/kTj)

P0 is the initial light output, P is the light output after heating and heating t time, β is the attenuation coefficient at a certain temperature, t is the power-on working time at a certain temperature, β0 is a constant, and Ea is the activation energy. , k is the Boltzmann constant, IF is the operating current, and Tj is the junction temperature.

• Through formula transformation and experimental data

Ea=[K×In(t2/t1)]/(1/Tj2-1/Tj1)

T2=t1×exp[Ea/K(1/Tj2-1/Tj1)

Thus, the failure at 25 ° C is judged to be 70% of the life expectancy.

Test sample problem

• The selection of sample models and specifications should be typical and representative.