Colour rendering

Depending on the location and the purpose, artificial light should enable colours to be perceived correctly as though being seen by natural daylight. Such assessments are based on the colour rendering properties of a light source, which are expressed in terms of the "general colour rendering index" Ra. The colour rendering index is a measure of the comparison between the chromaticity of an object under the light source being measured and its chromaticity under a reference light source.

Colour rendering property Colour rendering group Colour rendering index Ra Typical lamp Excellent 1 A 90 Tungsten halogen lamps, LUMILUX DE LUXE fluorescent lampsHQI.../D Very good 1 B 80 - 89 LUMILUX fluorescent lamps HQI.../NDL or WDL Good 2 A 70 - 79 Basic fluorescent lamps (25) Satisfactory 2 B 60 - 69 Basic fluorescent lamps (20,23,30) Fair 3 40 - 59 HQL Poor 4 39 High-pressure and low-pressure sodium discharge lamps
The chromaticity of eight (or 14) test colours standardized in DIN 6169 that occur when they are illuminated by the light source being tested are compared with the same test colour when illuminated by the reference light source. The smaller the difference the better the colour rendering property of the lamp being tested. A light source with an Ra value of 100 shows all the colours perfectly, as in the case of the reference light source. The lower the Ra value, the worse the colour rendering.
Test colours for Ra8 R1 Old rose   R5 Turquoise   R2 Mustard yellow   R6 Sky blue   R3 Yellow-green   R7 Violet   R4 Light green   R8 Lilac   Additional test colours with saturated colours (Ra14) R9 Red   R12 Blue   R10 Yellow   R13 Skin tone   R11 Green   R14 Leaf green