Investigation On Surface-luminance Measurement Of Light-emitting Diodes And Development Of Luminance Analysis System

Light-emitting diode(LED)is a miniature light emitting device of PN junction.Because of its high luminous efficiency,long life,small size and manyothe radvantages,LED is destined to play an important role in general lighting field and special lightingfiled in the future.However,LED cannot produceuniform lightsdue to the unique dimensions of its luminous surface,leading to some consistency difference in luminance of LED chip.The traditional luminance test method only focuses on the total value of LED luminance,but with no concern about the luminous details of the chip surface.Therefore,how to achieve luminance uniformity detection of the LED chip more efficiently and moreconveniently has become an important research topic.Under such situation,two aspects of research has been carried out in this article.1.Proposing a novel method for measuring surface-luminance of LED bare chip.Firstly,based on the photographic and photometric theory,weput forward a relationship between the luminance of LED and the exposure time of digital camera and the gray-value of captured image.Then,a theoretical model for testing the surface-luminance of LED chips is constructed.Secondly,in order to reduce the test error and improve the test accuracy,the dark current and non-uniformity calibrations of entire luminance test system were carried out.Through the curve fitting of the image gray value and the actual luminance,the reliability of our model can be verified according to the value of R-squared.Thirdly,using such method to carryout numerousmeasurements,and randomly selected a series of measured-luminanceand standard-luminance at different electrical currents for error analysis,proved that such method has the advantage of high test accuracy.2.Developing a LED luminance uniformity analysis system software.LED luminance uniformity analysis system which developed by DELPHI is a visualization software for analyzing the surface-luminance distribution of LED chips.It is convenient to use such a software due to itsversatility,including camera control,image processing,graphics rendering and real-time luminance measurement.The micrograph of the LED chip obtained in the darkroom can be imported into the software to generate pseudo images and the surface-luminance distribution can also be analyzed simultaneously.The system can not only reflect the uniformity of the luminance distribution on LED surface,but also realize the qualitative and quantitative analysis of the surface-luminancedistribution.This software can provide an important reference for electrode pattern design,thus ensuring the reliability of LED quality.