Testing standards for optoelectronic performance of LED products

　　1. Electrical characteristics

　　The electrical characteristic parameters of LED include forward current, forward voltage, reverse current and reverse voltage. This test is generally carried out using a voltage and current meter under the condition of constant current and constant voltage power supply. Through the test of LED electrical characteristics, the maximum allowable forward voltage, forward current and reverse voltage and current parameters can be obtained. In addition, the optimal working power value of LED can also be obtained.

　　2. Optical properties

　　It mainly includes luminous flux and luminous efficiency, light intensity and light intensity distribution characteristics and spectral parameters.

　　Luminous flux and luminous efficacy: There are usually two methods, the integrating sphere method and the variable angle photometer method. Although the latter has the most accurate test results, the former is generally used because it takes a long time. When testing with the integrating sphere method, the LED to be tested can be placed at the center of the sphere or on the wall of the sphere. After measuring the luminous flux, the luminous efficiency of the LED, that is, the luminous efficacy, can be measured with an electrical parameter tester.

　　Light intensity and light intensity distribution characteristics: Since the light intensity distribution of LED is inconsistent, its test results vary with the test distance and the size of the detector aperture. The light intensity of each LED can be tested and evaluated under the same conditions, so that the results are more accurate.

　　Spectral parameters: mainly include peak emission wavelength, spectral radiation bandwidth and spectral power distribution. The spectral characteristics of LED can be represented by spectral power distribution, and chromaticity parameters can also be obtained through spectral power distribution. Generally, the test of spectral power distribution needs to be carried out by spectroscopic analysis, and the monochromatic light in the mixed light is distinguished one by one for measurement. Prisms and gratings can be used to achieve spectroscopic analysis.

　　3. Switching characteristics

　　It refers to the light, electricity and color change characteristics of the LED when the power is turned on and off. Through this test, we can get the changing rules of the LED's working state, material properties, etc. at the moment of power on and off, so as to understand the loss of the LED caused by power on and off.

　　4. Color characteristics

　　The main ones include chromaticity coordinates, dominant wavelength, color purity, color temperature and color rendering, etc. The testing methods include spectrophotometry and integration method.

　　Spectrophotometry: The LED spectral power distribution is measured by spectrophotometry with a monochromator, and then the corresponding chromaticity parameters are obtained by integrating the chromaticity weighted function.

　　Integration method: Use specific color filters and photodetectors to directly measure chromaticity parameters.

　　5. Thermal properties

　　It also refers to thermal resistance and junction temperature. Thermal resistance refers to the ratio of the temperature difference along the heat flow channel to the power dissipated in the channel. Junction temperature refers to the PN junction temperature of the LED. There are two ways to test the LED junction temperature. One is to use an infrared temperature measuring microscope or a micro thermocouple to measure the surface temperature of the LED chip . The other is to use the inverse relationship between the forward bias voltage and the junction temperature under a certain current to determine the junction temperature of the LED.