Spectral power distribution of D65.

CIE Standard Illuminant D65 (sometimes written D₆₅^[1][2]) is a commonly-used standard illuminant defined by the International Commission on Illumination (CIE).^[3] It is part of the D series of illuminants that try to portray standard illumination conditions at open-air in different parts of the world.

D65 corresponds roughly to a mid-day sun in Western Europe / Northern Europe, hence it is also called a daylight illuminant. As any standard illuminant is represented as a table of averaged spectrophotometric data, any light source which statistically has the same relative spectral power distribution (SPD) can be considered a D65 light source. There are no actual D65 light sources, only simulators. The quality of a simulator can be assessed with the CIE Metamerism Index.^[4][5]

The CIE positions D65 as the standard daylight illuminant:

Relative spectral power distribution of illuminant D and a black body of the same correlated color temperature, normalized about 560nm.

History

The CIE introduced three standard illuminants in 1931:

• A: Incandescent bulb simulator
• B: Daylight simulator (direct)
• C: Daylight simulator (shade)

B and C were derived from A by using liquid filters. The approximation to real light this provided was found lacking, so in 1967 the CIE accepted a proposal by Judd, MacAdam, and Wyszecki for a new series of daylight simulators, bearing the initial D.^[6][7][8]

Definition

D65 is a tabulated SPD in increments of 5nm from 300nm to 830nm, using linear interpolation on the original data binned at 10nm.^[9][10] The CIE recommends using linear interpolation of the component SPDs, S₀, S₁, and S₂ if the application requires greater precision, but there is a proposal to use spline interpolation instead.^[11]

The CIE 1931 color space chromaticity coordinates of D65 are x=0.31271, y=0.32902 using the standard observer and x=0.31382, y=0.33100 using the supplementary observer. Normalizing for relative luminance, the XYZ tristimulus values are X=95.04, Y=100.00, Z=108.88. Since D65 represents white light, its co-ordinates are also a white point, corresponding to a correlated color temperature of 6504 K. Rec. 709, used in HDTV systems, truncates the CIE 1931 coordinates to x=0.3127, y=0.3290.

Why 6504 K?

Chromaticity of D₅₀, D₅₅, and D₆₅ as points on the daylight locus in the CIE 1960 UCS.

References

1. ↑
2. ↑
3. ↑ ^{a b}
4. ↑
5. ↑
6. ↑
7. ↑
8. ↑
9. ↑ CIE. Relative SPD of D65, 300?780nm in 5nm increments.
10. ↑ Relative SPD of D65, 300?830nm in 1nm increments. Derived by linear interpolation of the 5nm table.
11. ↑

External links

• Selected colorimetric tables in Excel. CIE.

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