LED product quality analysis and judgment standard

In order to develop LED technology, developed countries attach great importance to the research of LED testing methods and standards. For example, detection of the American National Standards Institute (NIST) research organization international testing experts to carry out LED testing, focus on the LED luminescence properties and temperature characteristics and attenuation characteristics of test methods, trying to establish a set of LED testing methods and technical standards, testing in LED has been at the forefront of the world.

Semiconductor light-emitting diode (LED) has many new problems in quality evaluation and detection methods because of its small size, directional emission, high brightness, and electrical characteristics of PN junction. Different applications, determines the performance requirements of LED products. From the optical performance, the display of the LED, mainly brightness, viewing angle distribution, color and other parameters. For the general lighting of the LED, pay more attention to luminous flux, beam spatial distribution, color, color rendering parameters and other parameters, and biological applications of LED, is more concerned about the biological effective radiation power, effective irradiance parameters. In addition, the light emitting diode is not only a kind of light source, but also a kind of power semiconductor device, so its quality must be evaluated from the aspects of optics, electricity and heat.

From the point of view of the current structure and industrial development of LED products, the main parameters of LED lighting products are optical properties, electrical properties, thermal properties, radiation safety and life expectancy.

Optical properties: the optical properties of LED are mainly related to the spectral, photometric and colorimetric performance requirements. According to the new industry standard "semiconductor light emitting diode, a test method of" main emission peak wavelength and spectral radiation bandwidth, axial luminous intensity, half intensity angle, beam flux, radiation flux, luminous efficiency, chromaticity coordinates, color temperature and color purity and dominant wavelength, color rendering index. Display LED, mainly intuitive visual effect, therefore the color temperature and color rendering index is not required, and lighting with white LED, it is particularly important to the two parameters, it is an important index of lighting atmosphere and effect, and the color purity and dominant wavelength are generally not required.

Electrical performance: LED the electrical characteristics of the PN junction, determines the LED in lighting applications different from the traditional electrical properties of the light source, that is, a single nonlinear conductivity characteristics, low voltage drive, as well as sensitive to static characteristics. At present, the main measurement parameters include forward drive current, forward voltage drop, reverse leakage current, reverse breakdown voltage and electrostatic sensitivity.

Thermal performance: LED lighting to enhance the luminous efficiency and power is one of the key problems of current LED industry development at the same time, PN junction temperature and shell heat of LED is particularly important, generally represented by the shell temperature, thermal resistance, junction temperature and other parameters.

Radiation safety: at present, the International Electrotechnical Commission IEC LED products equivalent to the requirements of semiconductor laser radiation safety testing and demonstration. Because LED is a narrow beam, high brightness light emitting device, taking into account the radiation may harm to the retina, therefore, for different applications of LED, the international standard specifies requirements and test methods for the value of effective radiation limit. Currently in the European Union and the United States, lighting LED products radiation safety as a mandatory safety requirements.

Reliability and longevity: the reliability index is a measure of the ability of LED to work in a variety of environments. Especially important in LCD backlight and large screen display. Life is a quality index that can be used to evaluate the available period of LED products. In lighting applications, the effective life is the duration of the LED when the luminous flux decays to the specified percentage of the initial value under the rated power.

LED industry should attach importance to the development of measurement standards

Luminous surface of small LED, high brightness, narrow beam determines the specificity of the detection, in order to deal with this problem, CIE has established a "TC2-45LED measurement and TC2-46CIE/ISOLED intensity measurement standard" two technical committee. The CIETC2-34 team met in Vienna in October 1997 to develop and recommend the CIE127-1997LED standard, which relates to LED radiometric, photometric and colorimetric measurements. However, due to the rapid development of LED technology in recent years, especially for white LED lighting products, many problems are not considered in the past. Therefore, held in Kyoto 1999 annual meeting of the CIE, the developed countries on behalf of the proposal, made by CIETC2-34 white LED lighting standard, the Japanese delegation also submitted a draft standard two white LED general lighting.

In order to develop LED technology, developed countries attach great importance to the research of LED testing methods and standards. For example, detection of the American National Standards Institute (NIST) research organization international testing experts to carry out LED testing, focus on the LED luminescence properties and temperature characteristics and attenuation characteristics of test methods, trying to establish a set of LED testing methods and technical standards, testing in LED has been at the forefront of the world. Japan set up a white light LED Test Research Committee, a special study of white LED lighting test methods and technical standards. The developed countries in the world in order to seize the commanding heights of LED research, in the LED standards and testing have invested a lot of manpower and material resources, in terms of standards to select the characteristics of the LED parameters and test methods.

In China, there are no corresponding national standards for the testing methods of semiconductor light-emitting diodes, so there is a lot of controversy between different manufacturers and users.