The CIE 1931 system of colorimetry uses the photopic luminous efficiency function V( l) as one of the It is possible to abandon the use of real primaries in favor of imaginary primaries that have some useful characteristics. Since it is known that the chromaticity of any light source can be determined by a linear combination of three primaries, In the u, v color space, the same distance between any two points are presumed to be perceptually equal. The CIE 1976 chromaticity diagram was constructed by mathematically transforming the x, y chromaticity coordinates to u, v: The blackbody locus represents the chromaticities of blackbodies having various (color) temperatures. In Figure 6, the spectral locus, the purple boundary, and the blackbody locus comprise the chromaticity diagram. Using x, y as the coordinates, a two-dimensional chromaticity diagram (the CIE 1931 color space diagram) can be plotted as shown in Figure 2. From X, Y and Z, the chromaticity coordinates x, y, z can be obtained as follows:įigure 1. The color-matching functions give the tristimulus value X,Y and Z: The 1931 CIE (x, y) chromaticity coordinates are calculated from the spectral power distribution of the light source and the CIE color-matching functions (Figure A-1). The color is also written in RGB and hexadecimal format.Īs with our Wavelength-Colour demo, the perception of colour by the the human eye depends not only on the wavelength of the incoming radiation but also on a number of additional factors (including psychological ones), so this scale should best be thought of as an approximation.The CIE approximation functions to the black-body curve (that results the CIE Dnnnn values) are about 1% off from the accurate blackbody curve. The slider above allows you to control the temperature, which in turn changes the display to the color of the light that would be emitted from an object at that temperature. Using the term "cool" to describe something glowing red hot could be thought of as a slight misnomer, but it helps you to understand that compared to blue-hot objects, red-hot objects certainly are cool! For the sake of this explanation, a "hot" object will have a temperature of around 15,000 Kelvin, a "warm" object will be at approximately 6,500 Kelvin and a "cool" object will be around 1,500 Kelvin.īlue light has a higher frequency than red light, so it follows that hot objects will glow bluish, warm objects will glow white (made up from a combination of blue and red light), and cool objects will glow red. In very simple terms, a hotter object emits more high frequency radiation than a less hot one. (If you're interested in the exact way in which this occurs, please head over to our demo of Planck's Law of Blackbody Radiation.) As an object heats up, it begins to emit light.
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