Color rendering index
Main article: Color rendering index
Color rendering index (CRI) is a measure of how well colors can be perceived using light from a source, relative to light from a reference source such as daylight or a blackbody of the same color temperature
. By definition, an incandescent lamp has a CRI of 100. Real-life fluorescent tubes achieve CRIs of anywhere from 50 to 99. Fluorescent lamps with low CRI have phosphors that emit too little red light. Skin appears less pink, and hence "unhealthy" compared with incandescent lighting. Colored objects appear muted. For example, a low CRI 6800 K halophosphate tube (an extreme example) will make reds appear dull red or even brown. Since the eye is relatively less efficient at detecting red light, an improvement in color rendering index, with increased energy in the red part of the spectrum, may reduce the overall luminous efficacy.
Lighting arrangements use fluorescent tubes in an assortment of tints of white. Sometimes[weasel words]
this is because of the lack of appreciation for the difference or importance of differing tube types.
Mixing tube types within fittings can improve the color reproduction of lower quality tubes.
Some of the least pleasant light comes from tubes containing the older, halophosphate-type phosphors
(chemical formula Ca5
). This phosphor mainly emits yellow and blue light, and relatively little green and red. In the absence of a reference, this mixture appears white to the eye, but the light has an incomplete spectrum
. The CRI of such lamps is around 60.
Since the 1990s, higher quality fluorescent lamps use either a higher CRI halophosphate coating, or a triphosphor
mixture, based on europium
ions, that have emission bands more evenly distributed over the spectrum of visible light. High CRI halophosphate and triphosphor tubes give a more natural color reproduction to the human eye. The CRI of such lamps is typically 82–100