White light is made up of all colour, which is why we see colour of objects evenly when lit by a balanced white light. If we reduce the output of any colour in a white light source, we reduce the reflective strength of that colour in objects. For example if we look at a ripe tomato under a blue light, we don’t see its red colour, because there is no red light available to reflect off it and onto our eyes. The ability to render colour fully and accurately is one major drawback with LED lighting that has not been designed correctly.
Color “Temperature” is a measure of the relative amounts of red or blue light being emitted. It is not a measure of temperature at all. Most commercially available LEDs aim to provide the highest luminous efficacy, meaning the brightest light output in Lumens for a standard of one watt of electricity used. These high powered LEDs use InGaN, GaN (gallium nitride) in the emitter and tend to produce the highest light output. The problem is there is a dominance of blue in the light, peaking at about 465nm and less of the red light that gives the impression of warmth. In order to correct this, the favoured method is to coat the InGaN emitter with phosphor of different colour. The phosphor absorbs the light energy and emits a more balanced output with a wider spectrum to produce white light. A fraction of the blue light undergoes the stocks fluorescence being transformed from shorter wavelengths to longer (500–700 nm.). Depending on the colour of the original LED, phosphors of different colour can be used. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively increasing the color rendering index (CRI) value of a given LED. These LED are called phosphor based white LEDs.