Blue LEDs with very high luminous intensity and shorter peak wavelength create new problems in their evaluation. Specially constructed photometers are needed for accurate evaluation.
The quantities in LED measurements are discussed and their measurement conditions clarified. Necessity of standards created from the same type of LEDs is emphasized. New recommendations of the CIE organization are mentioned.
LEDs are light- and near-infrared emitting diodes. Their line-like emission spectra causes considerable difficulties, not unlike phosphor emission of color CTRs, when accurate color measurement is required. LEDs exhibit many different spatial distribution characteristics as well, requiring relatively large area, uniform detector surface for photometric and colorimetric evaluation. Discussion of several diffferent type of colorimeters follows, showing trade-off between precision and price as well as suitability in their application for many different situations.
Special glass-filters are designed for imaging colorimetric purposes using full-filter technology. Spectral characterization of a CCD camera is performed and a CIELUV chroma difference map is used to characterize a globally filtered detector.
Color measurement techniques are discussed, comparing chromaticity coordinate values obtained by two different methods. Tristimulus (TS) colorimeters based on detectors matched with specialized filters exhibiting response curves like the CIE color matching functions are simpler and yet useful tools for most industrial applications. Limitations in their applicability is also shown.
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