The colour quality of a lamp or an illuminant with nearly white light is characterised by two features:
Light colour of the illuminant,
Colour rendering – identified through the colour rendering index – which impacts the chromatic appearance of objects and persons illuminated by said illuminant.
An illuminant’s light colour is expressed through the closest colour temperature Tcp (température de couleur proximale). The closest colour temperature is the temperature required for heated platinum to appear in the same colour as the light source (see fig.).
Figure 3.30: Extract from the chromaticity diagram according to CIE with Planckian curve representing the light colour of heated platinum. The closest colour temperatures in Kelvin (K) as well as approximate chromaticity coordinates of light colours, e.g. for fluorescent lamps, are charted. E is the white point.
Table 3.13: Light colour and closest colour temperature of lamps according to EN 12464-1
Low colour temperatures are used to describe warm light colours appearing in yellowish red/white e.g. candles, halide lamps and other thermal radiators. High colour temperatures are used to describe cold light colours appearing in blue-white (see table), such as daylight with roughly 6.500 K (clouded sky).
EN 12464-1 (see chapter ) does not recommend any light colours for the illuminants to be used, since their selection is strongly dependent on psychology, aesthetics and what is considered normal in the various regions of Europe. The selection of the suitable light colour for the illuminant also depends on illuminance levels, the colours of the room and the furniture, the surrounding climate as well as the application scenario. In warm climates, a higher colour temperature such as daylight white is generally preferred, in cold climates people prefer a lower colour temperature as present in warm white light colours. For most visual tasks, the light colours warm white and neutral white, which are preferred around Central Europe, are recommended.
