white light

white light

This data is reviewed by the project of data compilation and application of Science Encyclopedia of science popularization in China.

Also known as white light, achromatic light, achromatic light. The visible light emitted by the thermoluminescent body when heated to 1500 ℃ is actually a mixture of various colored lights. Can be in the spectrum of three primary colors of light: blue, red and green, according to a certain proportion of mixed white light. The mixture of all visible light in the spectrum is also white.

The composition of white light

When light is divided into different wavelengths by a white prism, or by a combination of different wavelengths, light is usually refracted into different wavelengths. If any two of the three primary colors overlap each other, intermediate colors will be produced, and the three primary colors will be mixed with each other to become white, so it is also called "additive three primary colors". Among the three primary colors, green is the most important, because green occupies 69% of the brightness of white, and is in the center of the color horizontal arrangement table. It can be seen from the chromaticity diagram (1931) published by the International Commission on illumination that white can also be synthesized by two colors of light, such as yellow and blue, or blue-green and red, although their spectral components are different.

Color deviation of white light

The light we can see is an electromagnetic wave. Electromagnetic wave is formed by energy, which propagates from space in the process of periodic change. People can't see light everywhere, but light travels at a certain wavelength. Because white is a mixed color, there is no identifiable wavelength value, so it is represented by its coordinate value on the chromaticity diagram. We define it as "cold white" and "warm white". In all kinds of colors, there is the problem of color deviation, among which blue and white are more obvious, especially white. When the color temperature is less than 3000K, the white light shows warm white (white with red), giving people a warm and steady feeling; when the color temperature is between 3000K and 5000K, the white light does not bias, giving people a refreshing feeling; when the color temperature is more than 5000K, the white light shows cold white (white with blue), giving people a cool feeling.

Realization of artificial white light

There are three ways for led to realize white light: one is to synthesize white light through the combination of red, green and blue primary color multi chip; the other is to use blue LED chip to excite yellow phosphor, which can synthesize white light from LED blue light and yellow green light emitted by phosphor; in order to improve color rendering characteristics, appropriate amount of red and green phosphor can be added; the third is to use ultraviolet LED (UVLED) to excite three primary color phosphor to synthesize white light. Nippon Yat Sen Co., Ltd. takes the lead in developing a white inganled light source, which is obtained by combining blue inganled with YAG phosphor. The blue light emitted from the LED chip is scattered in the phosphor layer for many times and partially absorbed by the phosphor. The phosphor is excited to produce green light with a peak wavelength of 550nm, which is combined with the transmitted blue light to form white light. Of course, according to chromaticity, red, green and blue LEDs can also be used to synthesize white light, namely three primary colors of white light. The cost of white LED made by these two methods is very high, because the main light source is blue and green LED with high price, which directly affects the promotion and application of devices.