Light color and color rendering
‘True’ colors do not exist
People tend to judge colors under what they consider to he natural or true lighting – conditions, often mistakenly using daylight for this purpose. But the colors seen under daylight on a Sunny day can be different to those seen on a day with overcast sky. For the spectral distribution of daylight is not constant, but is continually changing from hour to hour and from season to season. The correct thing to do, of course, is to assess the colors under the same type of lighting as that existing in the area where they will be finally seen.
For example, an evening dress should be chosen under incandescent lighting, for this is the sort of lighting most likely to be employed at the evening function where it will be worn. Similarly, the internal color scheme for an office should preferably be chosen under lighting identical to that which will later be installed there.
The spectral distribution of the light determines the color characteristics
It is the spectral distribution of the visible radiation, which determines both the color impression and the color rendering capability of light. This criterion is becoming increasing importance as new lamps, each having its own specific color characteristics, appear on the market, As the choice becomes greater, so too does the difficulty of deciding on the right lamp for a particular lighting situation.
Relation between light color and preferred lighting level
The choice of light source for a particular situation is also related to the lighting level employed. Warm-colored light (low color temperature) is associated with warmth and is preferred at low lighting levels (as in sunset), while cool light (high color temperature) is experienced as being more natural when the lighting level is relatively high. This is why cool, bright light is so popular in the tropics and subtropics (where daylight levels are naturally high), whereas in more temperate climates precisely the opposite is true.
The color characteristics of lamps, as specified in recommendations, are generally expressed in terms of:
4color temperature in Kelvin (K);
4 color rendering index (Ra).