CIE standard illuminants (original) (raw)

Author: the photonics expert (RP)

Definition: standardized optical spectra for white light sources

Categories: article belongs to category light detection and characterization light detection and characterization, article belongs to category vision, displays and imaging vision, displays and imaging

Related: white lightwhite light sourcescolor temperaturecolorimetry

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DOI: 10.61835/6ho Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn

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Contents

What are CIE Standard Illuminants?

The CIE (Commission Internationale de l'Éclairage = International Commission on Illumination) has defined various standard illuminants with different types of white light. These can be used as standard light sources both in calculations of colorimetry and in experimental measurements, using real light sources which will approximate those standard illuminants.

Each white illuminant has a certain white point which is not fully characterized by the correlated color temperature alone. For the standard illuminants, chromaticity coordinates in different color spaces are available.

Versions of Standard Illuminants

Standard Illuminant A

Standard illuminant A is closely matched by tungsten incandescent lamps (including halogen lamps) with a color temperature of 2856 K. It thus represents a typical situation with incandescent lighting, although in practice the color temperatures can be significantly lower or higher.

Standard Illuminants B and C

Standard illuminant B approximates daylight at noon with a correlated color temperature of 4874 K. Similarly, standard illuminant C approximates average daylight with a higher color temperature of 6774 K (due to a relatively stronger contribution of the blue sky).

Illuminants B and C were later deprecated in favor of the illuminant series D.

Standard Illuminant D Series

Standard illuminant D series is a more realistic approximation of daylight than the earlier versions B and C, but is more difficult to produce technically. CIE has defined rules for calculating the chromaticity coordinates of illuminant D for different color temperatures. A particularly important version, used as a standard in various circumstances, is illuminant D65 with a correlated color temperature of 6504 K.

Standard Illuminant E

Standard illuminant E has a constant spectral exitance (in terms of ($M_{\textrm{e},\lambda}$)) throughout the visible spectrum. It leads to chromaticity coordinates of (1/3, 1/3) in CIE XYZ color space. The correlated color temperature is 5455 K.

Standard Illuminant F Series

Standard illuminant series F has been designed to represent fluorescent lamps with various common types of phosphors.

Standard Illuminant LED Series

Similarly, a new series of standard illuminants for LED lighting has been published in 2018, as LED lighting is getting increasingly common.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What are CIE standard illuminants?

They are standardized spectral power distributions of light defined by the International Commission on Illumination (CIE). They serve as references for colorimetric calculations and for experimental setups using real light sources that approximate their properties.

What is the difference between the various series of illuminants (A, D, F, etc.)?

Each series represents a different type of light source. For example, illuminant A represents tungsten incandescent lamps, the D series represents various phases of natural daylight, the F series represents fluorescent lamps, and a new series represents LED lighting.

Which standard illuminant represents average daylight?

Illuminant D65 is a very common standard representing average daylight, with a correlated color temperature of about 6504 K. The earlier illuminants B and C were also for daylight but are now deprecated.

Are there standard illuminants for modern light sources like LEDs?

Yes, as LED lighting became more common, the CIE published a new series of standard illuminants in 2018 to represent the spectral characteristics of various common types of LEDs.

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