Standard Illuminants

Synonyms

CIE standard illuminant

Related Concepts

Chromaticity

Definition

A standard illuminant, as defined by the International Commission on Illumination (Commission International de L'Eclairage, abbreviated as the CIE), denotes a specific relative distribution of energy (“spectral power distribution”) for an illuminant, over the range 300–830 nm [3].

Background

The motivation for a definition of standard illuminants arises from the need for accurate measurement of the colors of objects. It is well understood that for a Lambertian surface with a spectral reflectance function given by r(λ), and under an illuminant given by i(λ), the three-vector of CIE XYZ tristimulus values is given by [8]:

$$\begin{array}{rcl} X &=& k\int_{\lambda} \bar{x}(\lambda) i(\lambda) r(\lambda) d\lambda \\ Y &=& k\int_{\lambda} \bar{y}(\lambda) i(\lambda) r(\lambda) d\lambda \\ Z &=& k\int_{\lambda} \bar{z}(\lambda) i(\lambda) r(\lambda) d\lambda, \end{array}$$

(1)

where $\bar{x}$, $\bar{y}$, $\bar{z}$...