Lighting, display, light source is three major applications for LED. Among them, LED display industry is the most mature one in terms of technology, product and market applications. Under the push of development law: technology progress and cost reduction. LED display industry chain can operate independently. In the past two years, as fund swarmed into LED upstream industry-LED chip display industry, manufacturers and makers began their crazy competitions for limited marketing resources. Below-cost sales occurred frequently. In the LED display market, despite that a few companies (display as their main business) are ready for listing, but there are also some LED display manufactures closed down. The economic crisis may be a factor, but the main reason is the limited resources but too intense competitions.
In the LED display chain, LED chip display industry is the most important link. Chip manufacture should pay more attention on how to improve the quality of their products and how to use these chips correctly. The process features of LEDs determine the importance of testing. Testing should run through the entire LED industry chain.
The processing and packaging of LED chips should be divided into several levels in accordance with wavelength (light color), brightness, reverse voltage, leakage current and other related parameters. Electronic parameter detections are the same as detections for LED (light-emitting diodes). Detection for wavelength and brightness are relatively hard than other parameters, need professional sorters. Luminance colorimeter is typically used in display factories, testing the wavelength and evenness of brightness of LED Panel Light chips. However, this kind of equipment has problems in accuracy and calibration. Normally used luminance colorimeters, like BM-7, CL-100, can reach a precision of three digitals after decimal point, which is not sufficient for wavelength measurement. Thus LED chips from different production processes will be hard to mix-use.
For commonly used LED screens, brightness variations less than 10% can hardly detected by human eyes, and color variations less than 4nm can hardly detected, neither. So that, the general classification standard for normal LED chips is brightness variations less than 20% and color variations less than 5nm. Brightness/color changes within this range will provide relatively ideal effects. For LED modules, brightness variations less than 3% and color variations less than 2nm can hardly detected by human eyes. Thus modules’ mix-usage has much strict requirements than LED chips’ mix-usage. Normally, producers need to take chrominance and luminance calibrations.