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