Solid-state lamps composed of coloured primary light-emitting diodes (LEDs) are promising sources of white light both for specialised and general lighting. Their unique features the capability of varying the colour temperature at a constant flux, dimming with constant chromaticity, and control of efficiency/colour-rendering trade-off. However, solid-state lamps based on the conventional trichromatic (red-green-blue, RGB) LED system suffer from inherent problems with colour rendering. In particular, it is difficult to achieve a uniform distribution of the special colour rendering indices because of incomplete coverage of the visible spectrum by three narrow-band primary LEDs. This drawback can be overcome in lamps containing a larger number of primary LEDs (quadrichromatic and quintichromatic lamps), which provide quasi-continuous spectra [1,2]. An optimised quadrichromatic red-ambcr-green-blue (RAGB) lamp with a uniform distribution of the special colour rendering indices has been already demonstrated [2], One of the key issues in the development of polychromatic solid-state lamps is the stability of the light parameters with respect to the variation of relative power of the primary LEDs, the variation in the peak wavelengths due to a spread in the semiconductor composition, and the variation the p-n junction temperature. In the present report, we address these issues by estimating the variations of correlated colour temperature (CCT) and the general colour rendering index (CRl) in a RAGB lamp.
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