Why do two light sources with the same white light and the same color temperature have different color reproduction effects?

1, color temperature-the color sign of light.

Take pictures with black and white film, as long as the aperture is fixed according to the intensity of light (the brightness of the object). However, when shooting with color film and color camera, besides the correct exposure, we should also consider the color temperature of the light that illuminates the subject, otherwise, color photos or color TV images will have color differences, and the color of the scene cannot be correctly restored. What is color temperature? The concept of color temperature cannot be understood literally, it is not "the temperature of color". Color temperature is a sign indicating the spectral composition of white light source.

As we said before, white light is composed of colored light. Most of the visible light in life is emitted by the radiator. Such as sunlight, lights and candles, can be regarded as white light. But the degree of white is different, because these light sources contain different spectral components (spectral components, that is, the color components of light). How is the value of color temperature specified? Scientists compare the light emitted by a light source with the light emitted by an absolute blackbody when it is heated to a certain temperature. When the color components are the same, the color temperature of the absolute black body is customized as the color temperature of the light source. Absolute black is also called complete radiator. Refers to an object that neither reflects nor transmits, but can absorb all radiation on it. Experiments show that when the blackbody is heated continuously and the temperature rises continuously, the light emitted is not white light, but colored light. The order of temperature change is from red to yellow to white to blue. The unit of color temperature is the first letter of kehvin), with -273℃ as the starting point, 1C per liter 1K (the international conference stipulates that neither k nor k should be written). 0C = 273K, 3200K = 2927℃, and human eyes have different color perception for light with different color temperatures.

Although the concept of color temperature is expressed by the color component of the light emitted by the radiator (absolute black body) after heating. But in fact, it can be considered that the color temperature of the light source is independent of the physical temperature of the light source. There is a simple reason. The color temperature of the light emitted by tungsten lamp is about 3200K K. When a layer of blue paper is covered on it, the color temperature of the light will increase to 5600K (the extent of increase depends on the deep line of the blue paper). Because after adding a layer of blue transparent paper, the color composition of the projected light will change, blue light will be more, red and green light will be absorbed by the blue paper, but the temperature of the lamp will not change. The color temperature of cold light source is high, but its temperature is not high.

The relationship between color photography and color camera and color temperature is very important. There is no color temperature problem in black-and-white photography and video shooting. Whether taking color photos, movies or TV, we should pay attention to the color temperature of the lighting source. Only in this way can we correctly restore the color of the TV picture or control the color of the picture.

When taking color photos, you can only take photos under daylight illumination with daylight color rolls, and only take photos under illumination (3200K) with light color rolls. At present, light-colored films are used in domestic movies. The color temperature requirement is about 3200K K, so when shooting in the sun, a color filter is needed to reduce the color temperature in front of the camera lens. This color filter is amber, which can reduce the color temperature of sunlight (about 5500K) to 3200 K.

2. The color temperature of sunlight is not fixed in a day, but changes regularly with time. It's low in the morning and evening and high at noon. The average color temperature of sunlight is 5600K, and artificial light sources also have different color temperature indicators. When developing positive films, the chromatic aberration of film photography caused by the change of color temperature from day to day can be corrected by light distribution. In TV camera shooting, it is mainly solved by adjusting the balance between black and white. Specific methods of adjusting the balance between black and white (omitted). Both outdoor natural light and indoor natural light are high color temperature light around 5600K, and indoor light is mainly skylight, which is higher than the color temperature of sunlight. The color temperature of indoor natural light has nothing to do with the lighting quality.

On sunny days, the direct sunlight time is between 9- 15 hours, and the proportion of red, green and blue in sunlight is basically the same, each accounting for 1/3. So it gives people a white feeling. Tungsten lamp and civil light bulbs have low color temperature. Among them, there are more red components, giving people a reddish feeling. Fluorescent lamps contain more blue-green components. Give people a feeling of turquoise.

The color temperature of the lamp changes with the voltage. When the voltage is high, the color temperature is high, and when the voltage is low, the color temperature side is low. The approximate number of the standard voltage is 220V V, and the low voltage of 3-2V has little effect, so the human eye will not notice it.

3. The influence of color temperature of light source on color reproduction of scenery.

We usually see the colors of various objects in white light. This is because people basically live in a white light environment. When colored objects are illuminated by different colors, the color of the objects will change, and the human eye is not sensitive to this change, because the human eye has color vision adaptation, but it is very sensitive to color cameras.

4, color temperature balance-different color temperature light sources are mixed.

At the shooting scene, sometimes two kinds of light with different color temperatures are mixed. For example, in the case of indoor natural light, the color temperature of indoor natural light is high, mainly the skylight outside the window and the reflected light of outdoor scenery. If the brightness of indoor natural light is not enough or ideal, it needs to be supplemented and decorated with artificial light. At this time, the light with lower color temperature is inconsistent with the indoor natural light with higher color temperature. At this time, using two color temperatures to unify the color temperature of light is called color temperature balance. There are two ways to balance the color temperature: one is to put a piece of blue paper in front of the lamp with low color temperature to make the color temperature of the lamp with low color temperature (3200K) close to the color temperature of indoor natural light, and the other is to use the lamp with high color temperature (such as dysprosium lamp), which is commonly used in making movies and TV series. Second, the color temperature of the internal natural light is close to the light, and the window is pasted with orange transparent paper. This method can be used in the case of small window area, with the advantages of improving the efficiency of light (no need to add paper) and reducing the brightness of light after adding transparent paper. The second advantage is that the brightness of the window is weakened, which is beneficial to the brightness balance.

5. Color temperature comparison table of various photographic (camera) light sources.

Artificial light is natural light.

Color temperature of light source (k) Color temperature of light source (k)

Candlelight 1900 sunrise and sunset 1850

Kerosene lamp half an hour before sunrise and sunset 2000 2350

Ordinary civil light bulb 2650 9: 00 to 15: 00 5500

Iodine tungsten lamp 3200 from 9: 00 to 65438+5000-4800 after 05: 00.

Tungsten lamp 3200 has an average sunshine of 5500.

Photographic glare light 3400 summer noon direct light 5800

Dysprosium lamp 5500 Direct light at noon in autumn 6000-6500

Blue sky shadow 12500 5000-6000

Blue sky light 19000-25000

Bo Yun Tiankong Light 13000

Yuntiandeng 7500-8500

Yintianguang 6400-7000