Because of its small volume, beaming light, high brightness （Brightness Meter）, environmental protection and energy saving and other LED characteristics, LED has been more widely liked and accepted by people. With the application of all kinds of LED (LED Testing) products becoming mature, and at the same time, the prices of LED chip continue to drop. Three years ago, the price of 1 watt LED chip is probably three dollars, but now it has fallen to less than $1, the price of some chips inTaiwanand the mainland is even 3 RMB each. With such a wide range of chip prices, we certainly hope to spend the least money to buy the best things. Then how to judge the quality of LED (LED Tester)? From the aspect of the optical properties, for LED used for displaying, mainly are parameters such as the brightness, perspective distribution, color (Colorimeter) and so on. For LED used for general lighting, we should pay more attention to parameters such as the flux, the spatial distribution of the beam, color, color-rendering characteristics and so on. For LED biological applications, we are more concerned about parameters such as the LED biological effective radiated power, effective radiation intensity of illuminance. In addition, LED is not only a kind of light source, but is a kind of power-type semiconductor device, so the quality must be comprehensively evaluated from the aspects of light, electricity, heat and other aspects.
The optical properties of LED (LED Test Instruments) mainly involve spectrum, the luminosity, color, and other aspects of the performance requirements. According to the new industry standard “test method for semiconductor led “, the main parameters are peak wavelength, spectral radiant bandwidth, luminous intensity, beam half intensity angles, flux (Flux Meter), radiation fluxes, the luminous efficiency, chromaticity coordinates, correlated color temperature (Color Temperature Meter), color purity and dominant wavelength, color rendering index. LED used for displaying is mainly the visual impression, so it does not make the request for the correlated color temperature and the color rendering index. But for LED used for lighting, the above two parameters are particularly important, they are the important indexes of the lighting atmosphere and effects, and color purity and dominant wavelength generally have no requirements.
The electrical characteristics of LED PN junction, determines the electrical (Electrical Safety Test) properties that LED differs from the traditional source for the lighting applications. Namely characteristics include one-way nonlinear conduction characteristics, low voltage driver and electrostatic sensitivity, etc. At present the main measuring parameters include positive drive current, and forward voltage drop, reverse leakage current (Leakage Current Test), reverse breakdown voltage and electrostatic sensitivity, etc.
LED Thermal Properties
The improvement of the luminous intensity and power of the LED used for lighting is one of the key problems for the LED industrial development. At the same time, the LED’s PN junction temperature and shell heat dissipation problems is particularly important, which are generally indicated by LED thermal resistance, shell temperature, junction temperature to express.
At present, the International Electro technical Commission IEC has conducted the radiation safety testing and verification for the LED products according to the requirements of semiconductor laser. For LED is the luminescent device with narrow beam, high brightness, considering the LED radiation may harm the human eye retina, LED application for different occasions, international standard specifies the requirements of the effective radiation limits and testing methods. At present in the European Union and theUnited States, the radiation safety of LED lighting products has been seen as mandatory safety requirements.
Reliability and Life
Reliability index is the measurement of the normal work ability of LED in all sorts of environments. It is particularly important in the liquid crystal back light and big screen display. Life (LED Aging Test) is the quality index that evaluates the available cycle of LED products, usually is indicated by effective life or end life. In lighting applications, the effective life means the duration of the time when the LED in the power rating conditions, the light attenuation of the flux arrives at the percentage of the initial value.
Through the above points, comprehensively judging the quality of a LED is the scientific and right method.