[Source: Gaogong LED 's " LED Good Products" magazine January issue ]
I. Introduction
In recent years, power LEDs have been promoted and applied in the lighting industry, and it is possible to replace energy-saving lamps within five years. The luminous lifetime of the well-known foreign manufacturers in their product manuals is usually L70, and the junction temperature is 80-90 °C.
To verify that L 7 0 of 5 0 0 h needs 6 years, the cost is very high. Therefore, the North American standard IES only needs to verify 3 sets of different TSs, and then predict the L70 by data extrapolation method through IES TM-21-11. More than 35000h can be. How many people can't say L70? Even if this method is adopted, it takes one year, and the cost of the three sets of tests needs at least 100,000 yuan.
In 2009, CREE reported the long-term test results. The white light LAMP had a light decay of about 5% at a junction temperature of 65 ° C. It took 5 years to confirm that the product L70 was greater than 50000 h, and it was expected to be 80-100,000 hours.
LED is a semiconductor device, and it can fully estimate its lumen maintenance life L70 by using the more mature accelerated life test method. It can refer to the standard.
In 2007, our center conducted a step stress and constant stress accelerated life test on Lumileds' 1 watt LED sample, confirming that the LED light decay is exponentially decayed, so that the Arrhenius equation can be used to predict L70 at different junction temperatures.
In 2008, our center carried out an accelerated life test on five kinds of monochromatic one-watt LEDs of red, green and blue used in the Olympic Water Cube Project, and evaluated whether the L70 could reach 50000h.
According to our years of experience in the accelerated life testing of semiconductor devices and hardware facilities, the high-temperature accelerated life test of small sample 1000h has been used, and good results have been achieved. It is expected that the lifetime of five monochromatic LEDs will be greater than that at °C using junction temperature. 50000h.
Below we use the 1 watt green light-2 sample produced by American CREE Company used in the Olympic Water Cube Project as an example to give accelerated life test steps and data processing methods.
Second, the data processing basis
The lumen maintenance life of an LED is the time it takes for the LED luminous flux to decay to its initial value or 50% under rated conditions. The accelerated life of an LED is the time it takes for the luminous flux to decay to an initial value of 70% or 50% under some acceleration stress.
Refer to several formulas cited and derived in the article "Research on LED Accelerated Life Test Methods" in the fifth issue of Information Technology and Standardization, 2009, including the formula for optical power decay, that is, when the LED is in a slow degraded mode, the output The change in power with operating time is expressed as an exponential function:
Pt = P0 exp(-βt) (1)
Where: P0 is the initial luminous flux (or optical power); Pt is the luminous flux (or optical power) corresponding to a certain working time after heating and heating; β is the degradation coefficient at a certain junction temperature; t is a certain junction temperature Working time.
The formula for calculating the activation energy is:
Where: Ea is the activation energy; Lc, i is the accelerated average life at different test environment temperatures; Tj, (i-1), Tj, i are the junction temperatures at different test ambient temperatures.
The formula for calculating the average life at a junction temperature is:
Where: Lc, 0 is the average working life at the junction temperature to be calculated; Tj, 0 is the junction temperature; Tj, i is the junction temperature of a certain accelerated life test temperature.
Third, the test steps
The step stress test is first performed to determine the appropriate ambient temperature for the accelerated life test.
We randomly selected 6 of the XR 7 0 9 0 - L 1 -power green LED samples from the test to perform the step stress test. According to the JEP118 standard, the test environment temperature of the step stress test starts from 75 ° C, the step gradient is 25 ° C, and the working hours of each working point device are tested after each step until all the samples are ineffective. The ambient temperature at which the accelerated life test was finally selected was analyzed to be 100 ° C and ° C.
Unfinished
For more information, please refer to the January issue of Gaogong LED 's " LED Good Products" magazine.
I. Introduction
In recent years, power LEDs have been promoted and applied in the lighting industry, and it is possible to replace energy-saving lamps within five years. The luminous lifetime of the well-known foreign manufacturers in their product manuals is usually L70, and the junction temperature is 80-90 °C.
To verify that L 7 0 of 5 0 0 h needs 6 years, the cost is very high. Therefore, the North American standard IES only needs to verify 3 sets of different TSs, and then predict the L70 by data extrapolation method through IES TM-21-11. More than 35000h can be. How many people can't say L70? Even if this method is adopted, it takes one year, and the cost of the three sets of tests needs at least 100,000 yuan.
In 2009, CREE reported the long-term test results. The white light LAMP had a light decay of about 5% at a junction temperature of 65 ° C. It took 5 years to confirm that the product L70 was greater than 50000 h, and it was expected to be 80-100,000 hours.
LED is a semiconductor device, and it can fully estimate its lumen maintenance life L70 by using the more mature accelerated life test method. It can refer to the standard.
In 2007, our center conducted a step stress and constant stress accelerated life test on Lumileds' 1 watt LED sample, confirming that the LED light decay is exponentially decayed, so that the Arrhenius equation can be used to predict L70 at different junction temperatures.
In 2008, our center carried out an accelerated life test on five kinds of monochromatic one-watt LEDs of red, green and blue used in the Olympic Water Cube Project, and evaluated whether the L70 could reach 50000h.
According to our years of experience in the accelerated life testing of semiconductor devices and hardware facilities, the high-temperature accelerated life test of small sample 1000h has been used, and good results have been achieved. It is expected that the lifetime of five monochromatic LEDs will be greater than that at °C using junction temperature. 50000h.
Below we use the 1 watt green light-2 sample produced by American CREE Company used in the Olympic Water Cube Project as an example to give accelerated life test steps and data processing methods.
Second, the data processing basis
The lumen maintenance life of an LED is the time it takes for the LED luminous flux to decay to its initial value or 50% under rated conditions. The accelerated life of an LED is the time it takes for the luminous flux to decay to an initial value of 70% or 50% under some acceleration stress.
Refer to several formulas cited and derived in the article "Research on LED Accelerated Life Test Methods" in the fifth issue of Information Technology and Standardization, 2009, including the formula for optical power decay, that is, when the LED is in a slow degraded mode, the output The change in power with operating time is expressed as an exponential function:
Pt = P0 exp(-βt) (1)
Where: P0 is the initial luminous flux (or optical power); Pt is the luminous flux (or optical power) corresponding to a certain working time after heating and heating; β is the degradation coefficient at a certain junction temperature; t is a certain junction temperature Working time.
The formula for calculating the activation energy is:
Where: Ea is the activation energy; Lc, i is the accelerated average life at different test environment temperatures; Tj, (i-1), Tj, i are the junction temperatures at different test ambient temperatures.
The formula for calculating the average life at a junction temperature is:
Where: Lc, 0 is the average working life at the junction temperature to be calculated; Tj, 0 is the junction temperature; Tj, i is the junction temperature of a certain accelerated life test temperature.
Third, the test steps
The step stress test is first performed to determine the appropriate ambient temperature for the accelerated life test.
We randomly selected 6 of the XR 7 0 9 0 - L 1 -power green LED samples from the test to perform the step stress test. According to the JEP118 standard, the test environment temperature of the step stress test starts from 75 ° C, the step gradient is 25 ° C, and the working hours of each working point device are tested after each step until all the samples are ineffective. The ambient temperature at which the accelerated life test was finally selected was analyzed to be 100 ° C and ° C.
Unfinished
For more information, please refer to the January issue of Gaogong LED 's " LED Good Products" magazine.
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