Light emitting diodes (LEDs) and solid state lighting (SSL) products that incorporate LEDs pose many measurement challenges compared with other lighting elements, such as traditional tungsten and fluorescent. Advanced optical radiation measurement equipment and new techniques are often required to determine basic photometric and colorimetric parameters for LEDs and SSL products.
Updated measurement instrumentation, calibration and performance characterization methods have allowed for improvement in the repeatability and reproducibility of measurements of average LED intensity, total luminous flux and colorimetric quantities. Lower uncertainty, detector-based standards provide a convenient transfer and monitoring from primary measurement standards.
High sensitivity spectroradiometers using backside-thinned charge-coupled device (CCD) detectors provide much improved sensitivity in the blue spectral region over previous array-based systems. This is very important for obtaining consistent photometric performance results from white SSL products. New methods of characterizing the integrated stray-light performance of these detector array-based spectroradiometers allows the determination of colorimetric quantities from narrow spectral emission LEDs to almost match the results obtained from double-grating, scanning spectroradiometers. Because LEDs and SSL products can have significant variation in color as a function of direction of the emitted light, measurements as a function of angle or goniometric characterization is required, further complicating the quality assessment. The use of high quality measurement instrumentation is a basic requirement but this alone does not assure that consistent and repeatable results will be obtained.