The Principle of Three Primary Colors in Colorimeter

The colorimeter is mainly based on its color light ternary principle and complementary color principle to detect the color and control the color quality of the product. None of the three primary colors can be combined with the other two colors. In addition, the three primary colors as the basic colors of colors can be mixed into various colors through the color gamut. In the process of color perception, the color of the light source is related to the three factors of the light source, the eyes and the brain. Therefore, the selection of the three primary colors of the color light involves factors such as the wavelength and energy of the light source, and the spectral response range of the human eye. However, from the energy point of view, the brightness of the mixed color light is superimposed, and the mixed color light must be brighter than each color light before the mixing. Only the color light with low brightness can be mixed with a relatively large number of colors as the primary color. Otherwise, the color light with high brightness is used as the primary color, and its addition is brighter, so that the color light with low brightness can never be mixed. The three primary colors are distributed in different regions of the visible spectrum. If they are concentrated in a certain region, they will not be able to mix more colors.

In the white light dispersion experiment of the colorimeter, we can observe that the three colors of red, green and blue are relatively uniformly distributed in the entire visible spectrum, and occupy a wide area. But if we adjust the prism angle of the experiment to narrow the spectrum, we will find that the area occupied by the corresponding color light will also change. In the narrowed spectrum of the colorimeter color experiment, it will be found that the obvious changes of red, green and blue light are the most significant, and the rest of the light colors gradually decrease, and some are about to disappear. Through the experiment, it can be concluded that the wavelength ranges of the three colors are: R（600~700nm），G（500~570nm），B（400~470nm）.

In color science, the entire visible spectrum is generally divided into blue, green and red regions for study. When mixed with red, green and blue light, yellow, cyan and magenta light can be obtained respectively. Magenta light is spectrally absent, and we call it an off-spectral color.

When the human eye sees an object, there are three types of color-sensing cells on the retina - red-sensing cells, green-sensing cells, and blue-sensing cells, which are sensitive to red light, green light, and blue light respectively. When one of the color-sensing cells is strongly stimulated, it will cause the excitement of the color-sensing cells, resulting in the feeling of the color. In the same way, in the process of colorimeter color measurement, the red color light stimulus is received inside the instrument, and red information will be sent to the microprocessor of the instrument. The three color-sensing cells of the human eye have the ability to synthesize colors. When a complex color light stimulates the human eye, the color-sensing cells of the human eye can decompose it into three monochromatic lights of red, green and blue, and then mix them into one color. It is because of this ability to combine colors that we can identify a wider range of colors than red, green, and blue.

In 1931, the International Commission on Illumination (CIE) stipulated the wavelengths of the three primary colors: λR=700.0nm, λG=546.1nm, λB=435.8nm. In color research, in order to facilitate qualitative analysis, white light is often regarded as being synthesized by the addition of three primary colors of red, green and blue.