We know that the illumination source has a great influence on the color of the object. Different light sources have their own spectral energy distribution and color, and the color of the surface of the object changes as they illuminate. In order to unify the understanding of color, it is first necessary to specify a standard illumination source. Because the color of the light source is closely related to the color temperature of the light source, CIE specifies the color temperature standards for four standard illuminators:
Standard illuminator A: represents the light emitted by the complete radiator at 2856K (X0=109.87, Y0=100.00, Z0=35.59);
Standard illuminant B: represents direct sunlight with a correlated color temperature of approximately 4874K (X0=99.09, Y0=100.00, Z0=85.32);
Standard illuminant C: represents the average daylight with a correlated color temperature of approximately 6774K, and the light color is approximately the daylight of the cloudy sky (X0=98.07, Y0=100.00, Z0=118.18);
Standard illuminant D65: represents daylight with a correlated color temperature of approximately 6504K (X0=95.05, Y0=100.00, Z0=108.91);
Standard Illumination D: Represents daylight other than standard illuminator D65.
The standard illuminant specified by CIE refers to the specific spectral energy distribution and is the specified color standard of the light source. It does not have to be provided directly by a light source, and it is not necessarily achieved with a certain light source. In order to meet the requirements of the standard illuminator specified by the CIE, a standard light source must also be specified to specifically achieve the spectral energy distribution required by the standard illuminator.
CIE recommends the following artificial light sources to achieve the standard illuminant specifications:
Standard light source A: Inflatable spiral tungsten filament lamp with a color temperature of 2856K, its light color is yellowish.
Standard light source B: The color temperature is 4874K, which consists of an A source and a B-type DG liquid filter. Light color is equivalent to noon daylight.
Standard light source C: The color temperature is 6774K, which is composed of A light source and a C-type DG liquid filter. The light color is equivalent to the sky light with clouds.
CIE standard illuminators A, B, and C are implemented by standard sources A, B, and C, but for standard illuminator D65, which simulates typical daylight, CIE does not currently recommend a corresponding standard source. Because its spectral energy distribution is currently not accurately realized by real light sources. The development of a standard light source corresponding to the standard illuminant D65 is currently underway internationally.
The three analog D65 artificial light sources that are currently being developed are: high-voltage xenon arc lamps with filters, incandescent lamps with filters, and fluorescent lamps. Their relative spectral energy distribution is consistent with D65. The high-voltage Xenon arc lamp with filter provides the best simulation. The simulation of the incandescent lamp with filter in the ultraviolet region is not ideal, and the simulation of fluorescent lamp is poor. . In order to meet the needs of fine color production activities, there is also a mixed light source consisting of a fluorescent lamp and an incandescent lamp with a filter called a D75 light source. Its color temperature can reach 7500K. Mainly used in the fine color discrimination work such as the original cotton rating.
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