In another thread the question emerged, where the LEDs with 5 or more dies of different colours are. (Kudos to Brian Drummond) The background is as follows:
RGB LEDs are very popular for creating colourful lighting effects. In fact, due to the three receptor types in the human eye virtually every possible colour we can perceive can be produced with a red, a green and a blue LED although the LEDs can produce only a very delimited section of the visible spectrum. With three colours it is even possible, provided a perfect mixture ratio, to produce a light perceived as a pure white. The human vision cannot recognise different light sources if they excite the three colour sensing cones in the eye at the same levels. This effect is called metamerism.
However the human can very well perceive the quality of light sources when light is being reflected by coloured surfaces or objects. Because the reflection of light on coloured surfaces is effectively a multiplication of the light spectrum with the remission spectrum of pigments. The remitted spectrum differs vastly for different sources of white light.
To cut a long story short: White light from RGB-LEDs is a mess. If you try to use it for general illumination purposes, colours of artwork are reduced to a greyish mélange and human skin looks like beeing afloat in a quarry pond for a week.
White LED having a blue chip and a conversion layer produce considerably better light for illumination but can't be tuned to produce light with different colour temperatures let alone pure colours.
While there are some LEDs with a white chip and three colour chips in one housing, those usually tend not to address a better colour rendering but to have a higher luminous flux at white light.
So the question with some additional words is:
Why are there no multichip LEDs (5 or more chips) for the production of light with higher colour rendering?
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