LED Measurement and Standards

Abstract

Light emitting diodes (LEDs) have been widely used in full-color displays, traffic signals, and backlighting for cell phones and also have considerable potential in general lighting applications [1]. It is highly desirable for LED manufacturers to have LED's characteristic parameters, including photometric parameters such as luminous intensity (Iv) and total luminous flux (F V ), colorimetric parameters such as chromaticity coordinates (x, y), peak wavelength (l p ) and dominant wavelength (l d ), and electrical parameters such as forward voltage (V F ), and reverse current (I R ), because of the necessity for quality management [2]. Measurement of LEDs differs greatly from conventional light sources because of the distinctive properties of LEDs such as asymmetrical light-emission profile, narrow spectral bandwidth, and temperature sensitivity [3][4][5]. The spectral power distributions and colorimetric parameters of LEDs are very important quantities for the characterization of LED light sources. The CIE (the Commission Internationale de l'Eclairage) has published a technical report, CIE 127, as a guide to the photometric and colorimetric measurement of LEDs. In CIE 127, colorimetric parameters are derived from spectral power distributions (SPD) measurement results. Accordingly, high-accuracy spectral measurement is especially important. The SPD measurements can be obtained by using the imaging spectroscopic technique [6]. Spectrometers in the colorimetric measurement of the light source include two types: mechanical scanning spectrometer and array spectrometer [7]. Compared to mechanical scanning spectrometers, the array spectrometers based on the charge-coupled device (CCD) can capture the whole spectral image at once. There are relevant research efforts on LED's photometric parameters testing and colorimetric parameters testing [8,9].With the improvement of the high power LED's performance and its luminous efficiency, LEDs have begun to gradually replace traditional light sources in the field of functional lighting with a rapid and strong momentum, especially in road lighting. Presently, a great number of light fixture manufacturers in the world have pioneered the trial use of LED road lights in the market and have launched demonstration projects in many places. However, the relevant measurement standards of LED road lights have not been issued at home or abroad LED Packaging for Lighting Applications: Design, Manufacturing and Testing, First Edition. Sheng Liu and Xiaobing Luo.