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Basic introduction

Semiconductor light emitting diode (LED) has been widely used in indicator light, signal lamp, instrument display, mobile phone backlight, vehicle light source and other occasions. With the continuous development of white LED technology, LED is more and more widely used in the field of lighting. In the past, there were no comprehensive national standards and industry standards for LED testing. In the production practice, only relative parameters were used as the basis. Different manufacturers, users and research institutions had a great controversy on this issue, which greatly affected the development of domestic LED industry.

Optical property measurement

Luminous flux

Method 1 integrating sphere spectroradiometer

Reference standard:

Cie84:1989 measurement of luminous flux;

IESNA lm79-08 electrical and photometric measurements of solid state lighting products

Method 2. Distribution photometer

Reference standard:

Cie84:1989 measurement of luminous flux;

IESNA lm79-08 electrical and photometric measurements of solid state lighting products

Test items:

Beam angle luminous efficiency luminous flux

Spectral power distribution, chromatic aberration peak wavelength

Luminous flux maintains color rendering index, color coordinate and color tolerance

Light intensity distribution (light distribution curve)

Methods: distribution photometer

Reference standard:

IESNA lm79-08 electrical and photometric measurements of solid state lighting products

CIE 121:1998 luminaire photometry and distribution photometry

CIE 043:1979 "testing of projection illuminance"

GB / T 9468 General requirements for measurement of distribution photometry of luminaires

GB / T 7002:2008 photometric testing of floodlighting luminaires

Test items:

Lamp energy efficiency, beam angle, light intensity distribution and brightness limit curve

Budget estimate curve, equal intensity distribution curve, total luminous flux and annular luminous flux of indoor lamps and lanterns

The results show that the curve of plane equal illuminance, circular isoluminous curve, and rectangular equal intensity curve of ballast lumen coefficient (BLF)

test method

LED is a single polarity PN junction diode composed of semiconductor inorganic materials. The relationship between voltage and current is called volt ampere characteristic. Led electrical characteristic parameters include forward current, forward voltage, reverse current and reverse voltage. Led must be driven by appropriate current and voltage to work normally (as shown in Figure 1). The maximum allowable forward voltage, forward current and reverse voltage and current of LED can be obtained by testing the electrical characteristics of LED. In addition, the best working power of LED can be measured.

The electrical characteristics of LED are usually tested by Voltmeter under the power supply of corresponding constant current and constant voltage source.

Optical property test

Similar to other light sources, the measurement of LED light characteristics mainly includes luminous flux, luminous efficiency, radiation flux, radiation efficiency, light intensity, light intensity distribution characteristics and spectral parameters.

Luminous flux and luminous efficiency

There are two methods for measuring luminous flux, namely integrating sphere method and variable angle photometer method. Variable angle photometer is the most accurate method to measure luminous flux, but because it takes a long time, the integrating sphere method is generally used to measure luminous flux. There are two kinds of test structures for LED luminous flux measurement by integrating sphere method. One is to place the LED at the center of the sphere, and the other is to place the LED on the wall.

When the integrating sphere method is used to measure luminous flux, the self absorption of 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 LED can be measured with the electrical parameter tester. The measurement method of radiation flux and radiation efficiency is similar to the measurement of luminous flux and luminous efficiency.

Light intensity and light intensity distribution characteristics

The light intensity of point light source is evenly distributed in all directions of space, and the test results received by detectors with different receiving aperture at different distances will not change. However, due to the inconsistent light intensity distribution of LED, the test results vary with the test distance and detector aperture. Therefore, cie-127 proposes two recommended test conditions to test and evaluate the light intensity of each LED under the same condition, as shown in Figure 5. At present, cie-127 recommended test conditions have been cited by LED manufacturers and testing institutions.

Spectral parameters

The spectral characteristic parameters of LED mainly include peak emission wavelength, spectral radiation bandwidth and spectral power distribution. The spectrum of monochromatic LED is a single peak, and its characteristics are expressed by peak wavelength and bandwidth, while the spectrum of white LED is composed of many monochromatic spectra. The spectral characteristics of all LEDs can be represented by spectral power distribution, and the spectral power distribution of white LEDs. The chromaticity parameters can also be calculated from the spectral power distribution of LED.

The measurement of spectral power distribution needs to be carried out by light splitting, which can distinguish the colored light from the mixed light. Generally, prism and grating can be used to achieve spectral power distribution.

Our strengths

1. With professional qualifications, experienced experts and technical team, to provide you with professional consulting and services.

2. It has advanced laboratory equipment to ensure the accuracy and reliability of test data.

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Semiconductor light emitting diode (LED) has been widely used in indicator light, signal lamp, instrument display, mobile phone backlight, vehicle light source and other occasions. With the continuous development of white LED technology, LED is more and more widely used in the field of lighting.

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