Types of Light
The two main colors in most light sources are orange-red or blue-teal, which will give you the relative warmth or coolness of white light. These colors make up 95% of the available light. In photography, the quality of light is as important as the availability of light. This means the color of the light is as important as how much is falling on and around the subject. When a photographer is getting ready to take a photo, he/she should always take a reading of the color of the light. This is as important as the rest of the settings. To understand how to read light, the photographer needs to know how to read the Kelvin scale.
The Kelvin (K) scale is simply a unit of measurement for temperature. In photography, we most often use it to measure the color temperature of a light source. Every light source gives off heat, and with that heat, there is a color associated with it. Due to this color cast, subjects that appear white in real life may not appear white in a photograph. This is because cameras have a hard time distinguishing between the different kinds of light. The diagram to the left gives you the most commonly used numbers for the Kelvin scale for photography
To understand how to use the Kelvin scale, a photographer needs to understand how to read the scale and how the camera makes its adjustments while using the scale. The camera will counteract the color cast given by the light source by adding the opposite color. This can be confusing due to its complex nature; the camera will use the numbers from the K scale, but just in reverse; 1,700K and 2,100K will now be adding blue-teal and 6,500K and 12,000M will be adding red-orange.
In the above diagram, the candle flame's color temperature is between 1,700K and 2,100K; this means that a candle flame has a color cast of red-orange. Giving off a red-orange color cast will make a white subject have a red-orange cast on the subject. The camera will add in a blue-teal tone to offset the red-orange cast. This will remove the color cast and make the white subject white; the same would be true if the color cast would be blue-teal.
As a photographer, this information is important in understanding how the image will turn out. Nowadays, many cameras come with auto white balance, which will do the same as working with the Kelvin scale.
The difference is, when using auto white balance, the camera is only reading an average of the light. So, it can get it wrong sometimes. Below is a diagram depicting the different auto white balances. There are several ways to set the white balance in-camera: AWB (auto white balance), CWB (custom White balance), White Balance by Preset (i.e., sunny, cloudy, fluorescent, tungsten, etc.), or White Balance by Kelvin.