What is the relationship between Lux, Lumen and Candeira? What effect does color temperature have on our life?

The luminous intensity is referred to as light intensity, and the international unit is Candeira (abbreviated as Candeira) cd. Lcd refers to the luminous flux emitted by a light source in a specified direction within a unit solid angle. When the light source radiates uniformly, the light intensity is I = f/ω, ω is the solid angle, and the unit is sphericity (sr). F is the luminous flux, and the unit is lumen. For point light source, I=F/4. Brightness refers to the brightness of the light-emitting surface, which refers to the ratio of the luminous intensity of the light-emitting surface in the specified direction to the area of the light-emitting surface perpendicular to the specified direction, and the unit is candela per square meter. For diffuse reflection surfaces, although the light intensity and luminous flux in all directions are different, the brightness in all directions is equal. The screen of a TV is similar to such a diffuse surface, so when you look at the image from all directions, you will have the same brightness. Lux (legal symbol lx) illuminance unit is the illuminance received at a distance of 1 m from the light source, and the light intensity of the light source is 1cd, commonly known as candlelight. That is, at the distance from the light source 1 m, the luminous flux received at the illumination of 1 m2 is 1lm. Lumens, a unit of luminous flux. A point light source with luminous intensity of 1 Candeira (cd) emits luminous flux of "1 lumen" in unit solid angle (1 sphericity), which is abbreviated as lm. What is color temperature? What effect does color temperature have on our vision? The unit of color temperature is degree K, that is, the unit of absolute temperature. -273 degrees Celsius is the absolute temperature of 0 degrees K, so the freezing point of water is 273 degrees K and the boiling point is 373 degrees K.

Color temperature is a phenomenon in nature. When the universe is in a star without the sun and any luminous body, the temperature at this time is 0 degrees K, that is, everything is black, like a black hole. When a substance is heated (for example, the sun burns to 5000 degrees K of the surface temperature), the energy radiated by the substance includes the spectrum of visible light, such as red, clear, yellow, green, blue, indigo, purple, infrared, ultraviolet, gamma, beta rays and other different spectra.

Color temperature is the surface temperature of the luminous body, and the frequency spectrum generated has nothing to do with the intensity of the light source, that is, the feeling that the light source looks when it shines on a piece of white paper; For example, a piece of white paper is red under the tungsten lamp, a little yellow under the fluorescent lamp (4500 degrees K) and a little purple at noon, so the scenic sea water in the equatorial region is particularly blue, blue to a little purple (about 13000 degrees k~ 15000 degrees K).

Take the tungsten filament bulb as an example. When the tungsten filament is electrified and heated to about 2,200, the light emitted is almost red. Fluorescent lamp electrons collide with phosphor, and the color temperature produced by the collision is about 4500 degrees K; The color temperature of p22 phosphor of standard crt TV is about 7,300 when it is hit by electrons. The color temperature of the computer monitor that we China people are used to is 9300. ..

Color temperature is the feeling of human eyes to luminous body or white reflector, and it is a feeling of physical, physiological, psychological and other complex factors, which also varies from person to person. The color temperature can be changed artificially in TV (luminous body) or photography (reflector). For example, in photography, we use a 3200-degree-K incandescent lamp (3200-degree-K), but we add a red filter to the lens to filter out a little red light, so that the color temperature of the photo looks higher. Similarly, we can also reduce a little red on TV (but too much reduction will also affect the performance of normal red) to make the picture look a little higher in color temperature.

Preference for color temperature varies from person to person, which is related to the scenery we see every day. For example, people near the equator usually see a frequency average color temperature of 1 1000 degrees k(8000 degrees k (dusk) ~ 17000 degrees k (noon)), so they prefer a high color temperature (it looks more realistic). People at higher latitudes (the average color temperature is about 6000 degrees K) prefer low color temperature (5600 degrees K or 6500 degrees K), that is, if you use a TV with high color temperature to express the scenery of the North Pole, it will look blue. On the contrary, if you watch subtropical customs on TV with low color temperature, you will feel a little red, so this is also the time when photographers want to do some color temperature adjustment with their own cameras. Choose the filter and the color temperature on the negative or vcam camera, and take into account the audience's display equipment (such as the color temperature on the TV or movie projector) to make the audience feel the most realistic scenery.

On the other hand, how is the color temperature of TV or display screen defined? Because the average color temperature of scenery in China is about 8,000 degrees K ~ 9,500 degrees K all year round, TV stations always take pictures with the color temperature of 9,300 degrees K when making programs. However, due to the difference in the usual color temperature between Europe and America, the average color temperature in the whole year is around 6000 degrees K, so when we look at those foreign films, we will find that 5600 degrees k~6500 degrees K is the most suitable for watching. Of course, this difference makes us feel that when we see the screens of computers or televisions in Europe and America, we feel that the color temperature is red and warm, and some of them are inappropriate.