Because the light emitted by most light sources is collectively referred to as white light, the color surface temperature or correlated color temperature of the light source is used to refer to the relative whiteness of the light color to quantify the light color performance of the light source. According to Max Planck's theory, a standard black body with complete absorption and radiation ability is heated, and the temperature gradually increases, and the luminosity also changes; - yellow-yellow-white-white-blue-white process. The temperature at which the black body is heated to the same or close to the light color as the light source is defined as the correlated color temperature of the light source, called the color temperature, in absolute temperature K (Kelvin or Kelvin) as the unit (K=℃+273.15). Therefore, when the black body is heated to red, the temperature is about 527°C, or 800K, and other temperatures affect the change of light color.

  The more blue the light color, the higher the color temperature; the redder the lower the color temperature. The light color of the painted light also changes with time: 40 minutes after sunrise, the light color is yellow, and the color temperature is 3,000K; at noon, the sun is snow-white, rising to 4,800-5,800K; at noon on a cloudy day, it is about 6,500K ; The light color is reddish before sunset, and the color temperature drops to 2,200K on paper. The correlated color temperature of other light sources, because the correlated color temperature is actually a black body radiation close to the light color of the light source, the evaluation value of the light color performance of the light source is not an accurate color comparison, so two light sources with the same color temperature value, There may still be a slight difference in the appearance of the light color. Color temperature alone cannot tell the color rendering ability of the light source to the object, or how the color of the object is reproduced under the light source.

Northern clear sky 8000-8500k

Cloudy 6500-7500k

Summer noon sunshine 5500k

Metal halide lamp 4000-4600k

Afternoon sunlight 4000k

Cool color camp light 4000-5000k

High pressure mercury lamp 3450-3750k

Warm color camp light 2500-3000k

3000k halogen lamp

Tungsten filament lamp 2700k

High pressure sodium lamp 1950-2250k

Candle light 2000k

  The color temperature of the light source is different, and the color of the light is also different. The color temperature below 3300K has a stable atmosphere and a warm feeling; the color temperature between 3000--5000K is an intermediate color temperature, which has a refreshing feeling; the color temperature above 5000K has a cold feeling. Different light colors of different light sources make up the best environment.

  Color temperature is the human eye's perception of a luminous body or a white reflective body. The color temperature can be changed artificially on TV (illuminator) or photography (reflector), for example, in photography we use a 3200K incandescent lamp (3200K), but we add a red filter to the lens Filtering through a little red light makes the photo look cooler; in the same way, we can reduce a little red on the TV (but reducing too much will also affect the performance of normal red) to make the picture look higher in color temperature.

  The preference for color temperature depends on the person, which is related to the scenery we see every day. For example, for people close to the equator, the average color temperature seen every day is 11000K (8000K (dusk) ~ 17000K (noon)), So people prefer high color temperature (looks more real), on the contrary, people in higher latitude areas (average color temperature about 6000K) prefer low color temperature (5600K or 6500K), that is to say, if you use a high color temperature If you use a TV with a low color temperature to show the arctic scenery, it will look bluish; on the contrary, if you use a TV with a low color temperature to watch the subtropical scenery, you will feel a little reddish.

  How is the color temperature of a TV or display screen defined? Because the average color temperature of the scenery in China is between 8000K and 9500K throughout the year, the TV station uses the color temperature of the audience as 9300K to take pictures in the production of the program. However, because of the differences in the usual color temperature in Europe and the United States, the average color temperature throughout the year is about 6000K as a reference, so when we look at those foreign films, we will find that 5600K ~ 6500K is the most suitable for viewing. Of course, this difference makes us feel that the color temperature is reddish and warm when we see the screens of computers or TVs in Europe and America.

  It means that people with black eyes see 9300K as white, but people with blue eyes see it as bluish, and people with 6500K with blue eyes see it as white.