Quality analysis and judgment standard of decrypted LED products

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 performance: performance requirements for the optical properties of LED mainly involves spectrum, luminosity and chroma etc.. 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.

The electrical properties of junction electrical characteristics of LED, LED determines the electrical properties different from the traditional light source in lighting applications is central, conductivity, low driving voltage and nonlinear one-way sensitivity to electrostatic characteristics. At present, the main measurement parameters include forward drive current, forward voltage drop, reverse leakage current, reverse breakdown voltage and electrostatic sensitivity.

Thermal properties: 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 product is equivalent to the requirements of laser diode safety testing and demonstration radiation. 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.

The life and reliability of: the ability to measure LED in various environments is the normal work of the reliability index. 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.

Pay attention to the development of measurement standards

LED light emitting surface of small, narrow beam, high brightness 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. To development of LED lighting technology, developed countries have attached great importance to and standard test method LED. 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, testing method of semiconductor light emitting diode there is no corresponding national standards, so often big dispute between different manufacturers and users. In recent years, China Guangxie optoelectronic devices branch gradually organized a number of semiconductor light emitting diode test method for academic discussion and communication, the industry gradually formed a unified understanding, and develop the industry standard SJ/T2355-2005 "unified semiconductor light emitting diode test method", has played an important role in communication, compare products in the industry. The standard not only adopted

Methods CIE127-1997 "MeasurementofLEDs"