Understanding Illuminants

Understanding Illuminants

An illuminant is a mathematical representation of a theoretical light source, used for calculating tristimulus values from a spectrophotometric measurement. The numbers represent relative power of the theoretical source for specific wavelengths in the visible spectrum. The relative power distribution of a real light sources may also be used for calculation, but difficult to standardize.

CIE Standard Illuminant A: Mathematical representation of tungsten halogen (incandescent). Color temperature: 2856K. Can be used to test metamerism. Simulates limited residential and commercial retail lighting.

CIE Standard Illuminant D65: Mathematical representation of average noon sky daylight. Color temperature: 6500K. Uses include general evaluation of color, metamerism testing, providing visual correlation with spectrophotometric instrumental readings, and conformance with global industry standards.

CIE Illuminant D50: Mathematical representation of ‘horizon’ daylight in the early morning or late afternoon. Color temperature: 5000K. Uses include general evaluation of color, metamerism testing, and evaluating color uniformity and quality in the graphic arts industry.

CIE Illuminant F2 (CWF-2): Mathematical representation of commercial, wide-band fluorescent (halophosphor) lamps used in developing countries and less frequently in the USA (Cool White Fluorescent). Color temperature: 4200K. Uses include metamerism testing. Simulates limited commercial lighting in the USA due to low initial cost but poor efficacy.

CIE Illuminant F11 (NBF-11): Mathematical representation of commercial, rare earth phosphor, narrow- or tri-band fluorescent used in the USA. Color temperature: 4000K. Uses include metamerism testing. In USA, equivalent to TL84.

Illuminant TL84: Mathematical representation of commercial, rare earth phosphor, narrow- or tri-band fluorescent used in Europe and the Pacific Rim. Color temperature: 4100K. Can be used to test metamerism. Simulates typical office or store lighting in Europe and the Pacific Rim.

CIE Illuminant F12 (U30): Mathematical representation of commercial, rare earth phosphor, narrow- or tri-band fluorescent. Color temperature: 3000K. Can be used to test metamerism. Simulates typical retail store lighting (USA equivalent of TL83).

Illuminant TL83: Mathematical representation of commercial, rare earth phosphor, narrow- or tri-band fluorescent used in Europe and the Pacific Rim. Color temperature: 3000K. Can be used to test metamerism. Simulates typical office or store lighting in Europe and the Pacific Rim.

Some additional illuminant tables found in X-Rite software:

Illuminant SPL (D65): Mathematical representation of D65 as simulated with a filtered tungsten halogen light source in the SpectraLight QC. Color temperature: 6500K. Uses include critical evaluation of color, metamerism testing, providing visual correlation with spectrophotometric instrumental readings, conformance with global industrial standards. Simulates noon sky daylight standard illuminant D65.

CIE Illuminant D75: Mathematical representation of north sky daylight. Color temperature: 7500K. Uses include general evaluation of color, metamerism testing, and visual evaluation of opaque materials as outlined by ASTM D1729. Simulates north sky daylight.

Illuminant SPL (D75): Mathematical representation of D75 as simulated with a filtered tungsten halogen light source in the SpectraLight III. Color temperature: 7500K. Uses include critical evaluation of color, metamerism testing, and visual evaluation of opaque materials as outlined by ASTM D 1729. Simulates north sky daylight.

Illuminant SPL (HOR): Mathematical representation of tungsten halogen light source found in SpectraLight (Horizon). Color temperature: 2300K. Uses include detecting flare and metamerism testing. Simulates dimmed incandescent lighting in residential or commercial spaces (for example, restaurant ‘mood lighting’).

Illuminant TL85: Mathematical representation of commercial, rare earth phosphor, narrow- or tri-band fluorescent used in Europe and the Pacific Rim. Color temperature: 5000K. Similar to CIE Illuminant F10. Uses include metamerism testing. Simulates typical office or store lighting in Europe and the Pacific Rim.