Colorimetry is used to characterize and quantify the color perception of the human eye. The characteristics of light which is emitted by radiation or remitted by any object and arriving at the human eye can be objectively measured with a spectrophotometer. But this measurement of the color stimulus φ[λ] doesn’t represent the human perception of color. Therefore, the CIE had standardized the spectral sensitivity of the human eye. The sensitivity functions x[λ], y[λ] and z[λ] are shown in the image below. The color stimulus φ[λ] is rated with each cone function x[λ], y[λ] and z[λ] to compute the CIE 1931 XYZ color space tristimulus values. Y is similar to the luminosity. Any color can be represented by these three values. Based on these fundamental values a translation in various color spaces is possible, e.g. [x, y], [L*, a*, b*] or [L*, u*, v*].