1. Electrical characteristics
The electrical characteristic parameters of the LED screen of the industrial display include forward current, forward voltage, reverse current and reverse voltage. This test is generally performed with a volt-ampere meter under the condition of constant current and constant voltage source power supply. The maximum allowable forward voltage, forward current, reverse voltage, and current parameters can be obtained through the test of the electrical characteristics of the LED. In addition, the best working electrical power value of the LED can also be obtained.
2. Light characteristics
It mainly includes luminous flux and luminous efficiency, luminous intensity and luminous intensity distribution characteristics, and spectral parameters.
Luminous flux and luminous efficiency: There are usually two methods, the integrating sphere method and the variable angle photometer method. Although the test result of the latter is the most accurate, the former is generally used due to its time-consuming process. When testing with the integrating sphere method, the tested LED can be placed in the center of the sphere or on the wall of the sphere. After the luminous flux is measured, the luminous efficiency of the LED can be measured with an electrical parameter tester, that is, the luminous efficiency.
Light intensity and light intensity distribution characteristics: Because the light intensity distribution of the LED is inconsistent, its test results vary with the test distance and the size of the detector aperture, which can allow each LED to perform light intensity test and evaluation under the same conditions. This result is more accurate.
Spectral parameters: mainly include peak emission wavelength, spectral radiation bandwidth and spectral power distribution. The spectral characteristics of the LED can be represented by the spectral power distribution, and the chromaticity parameters can also be obtained through the spectral power distribution. Generally, the test of spectral power distribution needs to be carried out by light splitting, and the monochromatic light in the mixed light is distinguished one by one for measurement. Prisms and gratings can be used to achieve light splitting.
3. Switching characteristics
It refers to the light, electricity, and color change characteristics of the LED at the moment of power-on and power-off. Through this test, the working state and material properties of the LED can be obtained at the moment of power-on and power-off, so as to understand the loss of the LED when the power is turned on and off.
4. Color characteristics
Mainly include chromaticity coordinates, dominant wavelength, color purity, color temperature and color rendering, etc. The test methods include spectrophotometry and integral method.
Spectrophotometry: The LED spectral power distribution is measured by a monochromator, and then the corresponding chromaticity parameters are obtained by integrating the chromaticity weighting function.
Integral method: Use a specific color filter with a photodetector to directly measure the chromaticity parameters.
5. Thermal characteristics
It also refers to the thermal resistance and junction temperature. The thermal resistance refers to the ratio of the temperature difference along the heat flow channel to the power dissipated on the channel, and the junction temperature refers to the PN junction temperature of the LED. There are two methods for testing the junction temperature of LEDs. One is to measure the surface temperature of the LED chip using an infrared temperature measuring microscope or a miniature thermocouple, and the other is to use the inversely proportional change between the forward bias voltage and the junction temperature under a certain current. The relationship to determine the junction temperature of the LED.
