IMPROVEMENT OF SPATIAL CHROMATICITY MEASUREMENT OF WHITE LED LUMINAIRES

摘要

The application of white LEDs is wider and wider in lighting, with the improvement of theirrnluminous efficiency. However, the non-uniformity of spatial chromaticity is one of the importantrnissues to white LED luminaires. The chromaticity non-uniformity might be caused by thernnon-uniformity of phosphor layer, effective optical depth inconsistence of blue beam excitationrnfrom chip in phosphor layer, dispersion of attached secondary optics, and interference of therncoating which is used to improve the reflecting and transparent performance of optical surface.rnThere are two methods for spatial chromaticity measurement of LED luminaires: arncolorimeter and spectroradiometer to be combined with the goniophotometer. A calibratedrnCCD spectroradiometer is generally used in the goniophotometer to get absolute spatialrnchromaticity. However, for low intensities, the exposure time of CCD and data transport limitsrnthe measuring speed. It will cost lots of time to measure the non-uniformity of the spatialrnchromaticity of LED luminaires. The advantages of broadband colorimetric measurement arernquick response, good repeatability and accurate measurements of chromaticity coordinates forrnthermal sources. However, the main disbenefit of those measurements which has to bernconcerned is colour mismatch of the detectors.rnFor white LED luminaires used in lighting, although chromaticity might be some variation inrnspace, the spectral distribution is generally very similar. Low cost CCD spectroradiometersrncould be used to measure the spectral distribution on the optical axis of the LED luminaire ofrninterest (generally in normal). The colour mismatch of the detectors with the spectral responserns_(xr)(λ), s_(xb)(λ), s_Y(λ), s_Z(λ) can be corrected based on the above spectral distribution, and thernaccuracy for the measurement of spatial chromaticity of LED luminaires could be improved.rnIn this way, the spatial chromaticity of both LED PAR lamp and LED luminaire isrninvestigated. The chromaticity values in several selected directions were measured by a highrnaccuracy scanning spectroradiometer, and the colorimeter in the goniophotometer at this workrnis used to determine non-uniformity of spatial chromaticity. And then the measuring results ofrncolorimeter could be corrected with the spectral distribution, which is measured by a portablernCCD spectroradiometer with 50 mm focus length. The results show that the uncertainty ofrnabsolute chromaticity coordinates could be reduced from 0.02 for Δx, Δy to 0.0015 for Δx, Δy.rnIn conclusion, it’s possible that the measurement of chromaticity of LED luminaires in fullrnspace could be implemented quickly in the colorimetric goniophotometer by using low costrnspectroradiometers.