Join Rick Allen Lippert for an in-depth discussion in this video Understanding color temperature, part of On Camera: Video Lighting for the Web.
Have you ever noticed that some white light looks different than others, how sunlight seems to be more on the blue side while a small night light looks kind of yellowish? That is because they have different color temperatures. In this movie I'm going to explain, simply enough I hope, why that is. Quick science lesson. Bear with me here because this really is a basic knowledge regarding lighting. A long time ago a British scientist named William Thomson the 1st Baron Kelvin, otherwise known as Lord Kelvin, figured out that different light sources emit different colors, and he assigned a temperature, measured in degrees Kelvin, so the rest of us could understand it.
In between light waves we cannot see-- infrared on one end of the spectrum with ultraviolet on the other--is the range of visible light. Candlelight has the lowest temperature, between 1 and 2000 degrees, and sunlight is the highest, between 5,000 and 10,000 degrees, or more depending on the time of day. Average sunlight is considered to be 5600 degrees Kelvin. In between those two extremes is fluorescent light that is typically about 4000 degrees.
It falls in the green range as the visible light color changes from red to blue. As you might imagine, green light isn't very flattering, so try not to use fluorescents. The lower temperatures are referred to as warm, while the higher temps are said to be cool. Confusing, I know. It seems backwards, but it has to do with how the light looks rather than the number. This matters to you because if you mix a bluish light--sunlight--with a reddish light like an incandescent lamp, you will end up looking funny.
Part of you will red and the other part of you will look blue. For that reason you should avoid mixing your light sources. Color balancing this type of shot can be very difficult to fix in the editing. All dedicated video cameras are designed for using lights at 3200 degrees Kelvin. That's the color temperature of most studio and professional portable lights. Your small handheld video camera may have a menu setting for white balance using different light sources, typically either sunlight or indoor light.
These settings help the camera produce more pleasing pictures. The cameras in your smartphone, tablet, or a webcam are strictly automatic. A trained human eye can detect variations in light color, but most humans just see it all as white. Cameras, however, aren't so forgiving. Sure, they automatically adjust the color balance, but by understanding the concept of color temperature, you can improve your picture quality. You're going to want to know more about this because we'll be using this information in the next movies.