1.Electrical characteristics

 

The electrical characteristics of the LED include forward current, forward voltage, reverse current, and reverse voltage. This test is generally performed using a voltage ammeter, in the case of a constant current constant voltage source. Through the test of the electrical characteristics of the LED, the parameters of the maximum allowable forward voltage, the forward current, and the reverse voltage and current can be obtained. In addition, the optimum working electric power value of the LED can be obtained.

 

2. Light characteristics

 

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

 

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

 

Light intensity and light intensity distribution characteristics: Because the light intensity distribution is inconsistent, the test results vary with the test distance and the size of the detector aperture, allowing each LED to be tested and evaluated 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 parameter can also be obtained by the spectral power distribution. Generally, the measurement of the spectral power distribution needs to be performed by splitting, and the monochromatic light in the mixed light is separated one by one for measurement, and the prism and the grating can be used for the 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 change rule of the working state and material properties of the LED at the moment of power-off and power-off can be obtained, so as to understand the loss of the LED by the power-off.

4. Color characteristics

 

There are mainly chromaticity coordinates, dominant wavelength, color purity, color temperature and color rendering. The test methods include spectrophotometry and integral method.

 

Spectrophotometry: The spectral power distribution of the LED is measured by monochromator spectrometry, and then the corresponding chromaticity parameters are obtained by integrating the chrominance weighting function.

 

Integral method: The chromaticity parameter is directly measured by using a specific color filter in conjunction with a photodetector.

 

5. Thermal characteristics

 

Also refers to the thermal resistance and junction temperature. Thermal resistance refers to the ratio of the temperature difference along the heat flow path to the power dissipated on the channel. The junction temperature refers to the PN junction temperature of the LED. There are two test methods for LED junction temperature. One is to measure the surface temperature of the LED chip by infrared temperature measurement microscope or micro thermocouple, and the other is to use the inverse ratio between the forward bias and the junction temperature under the determined current. The relationship is used to determine the junction temperature of the LED.