LED photoelectric performance testing
basic introduction
Semiconductor light-emitting diodes (LEDs) have been widely used in indicators, signal lights, instrument displays, mobile phone backlights, vehicle light sources and other occasions. White LED technology is also constantly developing, and LEDs are increasingly used in the lighting field. In the past, there were no comprehensive national standards and industry standards for LED testing. In production practice, it could only be based on relative parameters. Different manufacturers, users, and research institutions were very controversial about this, which resulted in the development of the domestic LED industry being greatly affected. Big impact.
Light performance measurement
Luminous flux
Method 1 Integrating sphere spectroradiometer
Guideline:
CIE84:1989 "Measurement of Luminous Flux";
IESNA LM79-08 "Electrical and Photometric Measurements of Solid State Lighting Products"
Method 2 Goniophotometer
Guideline:
CIE84:1989 "Measurement of Luminous Flux";
IESNA LM79-08 "Electrical and Photometric Measurements of Solid State Lighting Products"
Test items:
Beam angle Light efficiency Luminous flux
Ring light pass Spectral power distribution Chromatic aberration Peak wavelength
Luminous flux maintenance Color rendering index Color coordinates Color tolerance

Light intensity distribution (light distribution curve)
Method Goniophotometer
Guideline:
IESNA LM79-08 "Electrical and Photometric Measurements of Solid State Lighting Products"
CIE 121: 1998 "Lamp Photometry and Goniophotometry"
CIE 043: 1979 "Test of Floodlight Luminance"
GB/T 9468 General requirements for goniophotometric measurement of lamps
GB/T 7002: 2008 Photometry test of floodlighting lamps
Test items:
Lamp energy efficiency, beam angle, lamp intensity distribution, brightness limit curve
Approximate curve of indoor lamps, equal light intensity distribution curve, total luminous flux, annular luminous flux

Plane isoluminance curve, circular isoluminance curve, ballast lumen factor (BLF), rectangular isoluminance curve

Test Methods
LED is a unipolar PN junction diode made of semiconductor inorganic materials. The relationship between its voltage and current is called volt-ampere characteristics. LED electrical characteristic parameters include forward current, forward voltage, reverse current and reverse voltage. LEDs must be driven by appropriate current and voltage to operate normally (as shown in Figure 1). By testing the electrical characteristics of the LED, the maximum allowable forward voltage, forward current and reverse voltage and current of the LED can be obtained. In addition, the optimal operating electrical power of the LED can also be determined.
The electrical characteristics of LEDs are generally tested using a voltage and ammeter under the power supply of the corresponding constant current and constant voltage source.
Optical characteristics test
Similar to other light sources, the test of LED light characteristics mainly includes luminous flux, luminous efficiency, radiant flux, radiant efficiency, light intensity, light intensity distribution characteristics and spectral parameters.

Luminous flux and light efficiency
There are two methods for testing luminous flux, namely the integrating sphere method and the variable angle photometer method. The variable angle photometer method is the most accurate method for testing luminous flux, but because it takes a long time, the integrating sphere method is generally used to test luminous flux. There are two test structures in the existing integrating sphere method for measuring LED luminous flux. One is to place the LED under test at the center of the sphere, and the other is to place it on the wall of the sphere.
When the integrating sphere method is used to test luminous flux, the self-absorption of light by the light source will affect the test results. Therefore, it is often necessary to introduce auxiliary lights.
After measuring the luminous flux, the luminous efficiency of the LED can be measured with an electrical parameter tester. The testing methods of radiant flux and radiant efficiency are similar to the testing of luminous flux and luminous efficiency.

Light intensity and light intensity distribution characteristics
The light intensity of the point light source is evenly distributed in all directions in space, and the test results obtained by using detectors with different receiving apertures at different distances will not change. However, due to the inconsistent light intensity distribution of LEDs, the test results vary with the test distance and detector aperture. Therefore, CIE-127 proposes two recommended test conditions so that each LED can be tested and evaluated for light intensity under the same conditions, as shown in Figure 5. Currently, CIE-127 recommended test conditions have been cited by various LED manufacturers and testing agencies.

Spectral parameters
The spectral characteristic parameters of LED mainly include peak emission wavelength, spectral radiation bandwidth and spectral power distribution. The spectrum of a monochromatic LED is a single peak, and its characteristics are expressed in terms of peak wavelength and bandwidth, while the spectrum of a white LED is synthesized from multiple monochromatic spectra. The spectral characteristics of all LEDs can be represented by spectral power distribution, white LED spectral power distribution. The chromaticity parameters can also be calculated from the spectral power distribution of the LED.
The test of spectral power distribution needs to be carried out through spectroscopy, which separates the various colors of light from the mixed light for measurement. Generally, prisms and gratings can be used to achieve spectroscopy.