8.4 UV radiation. Osram HQI-E 150 W/NDL CL
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Larger deviations are associated with a clear tint. The distance to Planck is also known as the chromaticity gap Δc.
Colour rendering is specified by irradiating defined test colours in succession with a reference source (an ideal
Planck radiator with the temperature and therefore colour temperature of the test light source) and with the test light source. The specific resultant colour shift ΔE i is defined for every test colour i in the uniform colour space CIE 1964 (W*, U*, V*).
Table 4: Test colours from DIN 6169
Testcolours
R1 – Dusky pink R2 – Mustard yellow
R3 – Yellow green R4 – Light green
R6 – Sky blue R5 – Turquoise blue
R7 – Aster violet R8 – Syringa violet
Saturated colours and additional test colours
R9 – Red
R11 – Green
R13 – Skin colour
R10 – Yellow
R12 – Blue
R14 – Leaf green
The specific colour rendering index R i
is defined as follows
R i
= 100 – 4.6 Δe
The arithmetic mean from the first 8 test colours
(see Table 4) shows the general colour rendering index
CRI or R a
.
i
Every special colour rendering index can therefore reach a maximum value of 100 when the test colour appears identical under reference and test light source. Negative values are also possible with greater deviations (and hence larger ΔE i
).
8.2.1 Test colours from standard DIN 6169
Apart from the first 8 colour rendering indexes,
DIN 6169 also defines other test colours, which are four saturated colours and additional test colours. The further test colours permit a more precise description of the colour rendering properties of the light source.
In principle it is possible to define any random number of many different test colours.
Table 5: Colour rendering levels
Evaluation Colour rendering level Colour rendering index CRI
Very good 1A ≥ 90
Very good 1B 80 – 89
Good
Good
2A
2B
70 – 79
60 – 69
Suboptimal
Suboptimal
3
4
40 – 59
20 – 39
The general colour rendering index results in the colour rendering levels for light sources given in
Table 5.
Thanks to a higher possible wall load, the colour rendering properties when using POWERBALL ® technology have been visibly improved compared to the lamp with cylindrical ceramic arc tube. A further improvement specific Color rendering index
HQI-T POWERSTAR
Typical lamp with cylindrical ceramic
Fig. 52: Comparison of the specific colour rendering indices for various metal halide lamps
49
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