The color temperature is defined as the light color radiated by a black body at different temperatures. When it is close to the light color of the light source, the relative color temperature of the light source is defined as the temperature of the black body. Kelvin believes that if a pure black object can absorb all the heat falling on it without loss, and at the same time can release all the energy generated by the heat in the form of “light”, it will be It changes into different colors by the height of heat.
When the color of the light emitted by the light source is the same as the color radiated by the black body at a certain temperature, the temperature of the black body is called the color temperature of the light source, and the absolute temperature K (Kelvim, or Kelvin temperature, K=℃+273.15) Express. Blackbody radiation theory is based on thermal radiation. Therefore, the spectral power distribution of thermal radiation sources such as incandescent lamps is relatively close to the spectral power distribution of black bodies in the visible region. They are both continuous spectrum. The concept of color temperature can completely describe this. The characteristics of the color of the similar light source.
When a black body (such as iron) is heated to a certain temperature, it starts to emit dark red light, and the color of the light becomes dark red, yellow-white, white, and blue-white when the temperature rises. For example, when the heat received by a black body is equivalent to 500~550℃, it will become dark red, and when it reache1050~1150℃, it will turn into yellow… Therefore, the color component of the light source is the same as the heat received by the black body. Corresponding to the temperature. A low color temperature is warm, and a high color temperature is cool. For example, the color temperature of candlelight is 2000K, and the color temperature of the sun at noon on a sunny day is 6500K.
According to MaxPlanck theory, heating a standard blackbody with complete absorption and radiation ability, the light color will change as the temperature gradually increases; the blackbody curve (Blackbodylocus) on the CIE color coordinate shows the process of black body from red to orange red to yellow to yellow and white to white to blue and white. The temperature at which the black body is heated to the same or close to the light color of the light source is defined as the correlated color temperature of the light source, and the unit is K. Since the gas discharge light source is generally a non-continuous spectrum, which cannot be completely consistent with the continuous spectrum of black body radiation, the correlated color temperature is used to approximate its color characteristics. When the color temperature is around 3000K, the light color becomes yellowish. Light sources with a color temperature (or correlated color temperature) below 3300K have a reddish color and give people a warm feeling. When the color temperature exceeds 5300K, the color is bluish, giving people a cool feeling. Lights of different color temperatures have different lighting and visual effects. Generally, people use light sources with a color temperature higher than 4000K in areas with higher temperatures, while light sources with a color temperature of less than 4000K are used in areas with lower temperatures. The correlated color temperature of different light source environments is shown in Table 1.
| light source | Color temperature (K) | light source | Color temperature (K) |
|---|---|---|---|
| Northern clear sky | 8000~8500 | High-pressure mercury lamp | 3450~3750 |
| cloudy day | 6500~7500 | Warm fluorescent lamp | 2500~3000 |
| Summer noon sun | 5500 | Halogen lamp | 3000 |
| Metal halide lamp | 4000~4600 | Tungsten lamp | 2700 |
| Afternoon daylight | 4000 | HPS | 1950~2250 |
| Cool fluorescent lamp | 4000~5000 | Candle light | 2000 |
The color temperature of the light source is different, and the light color is also different. The color temperature below 3300K has a stable atmosphere and a warm feeling; the color temperature is 3000~5000K as the intermediate color temperature, which has a refreshing feeling; the color temperature above 5000K has a cold feeling. The best environment composed of different light colors of different light sources is shown in Table 2.
| Color temperature (K) | Light color | Atmospheric effect |
|---|---|---|
| ＞5000 | Cool (white with blue) | Cold atmosphere |
| 3300~5000 | Middle (white) | Refreshing atmosphere |
| ＜3300 | Warm (reddish white) | Calm atmosphere |
Under the illumination of a high color temperature light source, if the brightness is not high, it will give people a cold atmosphere; under the illumination of a low color temperature light source, the brightness will be too high to give people a sultry feeling. Using two light sources with large light color difference in the same space will have a gradation effect. When the light color contrast is large, the brightness level can be obtained while the light color level is obtained. Different color temperatures will cause people to have different emotional reactions. Generally, the color temperature of the light source is divided into three categories:
(1) Warm color light. The color temperature of warm light is below 3300K, and the color of warm light is similar to that of incandescent light. There are more red light components, giving people a warm, healthy and comfortable feeling. It is suitable for homes, houses, dormitories, hospitals, hotels and other places, or temperature comparison Low place.
(2) Warm white light. Also called intermediate color, its color temperature is 3300~5300K. The warm white light is soft, which makes people feel happy, comfortable and serene. It is suitable for shops, hospitals, offices, restaurants, restaurants, waiting rooms and other places.
(3) Cool color light. It is also called daylight color. Its color temperature is above 5300K. The light source is close to natural light. It has a bright feeling and makes people concentrate. It is suitable for offices, meeting rooms, classrooms, drawing rooms, design rooms, library reading rooms, exhibition windows, etc. place.