Understanding White Balance
In order to understand light, you need to understand that light consists of color. The light that illuminates our world is made up of three primary colors: red, green, and blue. The combination of these colors impacts how the color in the scene you’re photographing is rendered by the camera. The quality of light can range from the cool blue of early morning to the warm, orange glow of sunset.
The color temperature of any light source is based on the experiments of British physicist William Kelvin, who discovered that a piece of carbon produced varying colors at different temperatures. On a scale ranging from 0 to 10,000 Kelvin, light at lower temperatures of 1,850K to 3,380K (candlelight, tungsten) produces a warm, reddish glow; higher temperature ranges, such as 7,000K to 10,000K (overcast, open shade), produce a bluish color cast.
If there is a baseline for color temperature, it’s direct sunlight, which has a color temperature of around 5,500K. This is the kind of light you probably find yourself shooting under on most days.
On an overcast day, with clouds that diffuse the rays from the sun, the light is cooler, with a color temperature of around 6,500K. This is a much cooler (or bluer) quality of light, which, if not corrected for, will produce a slight bluish tint in all colors, especially skin tones.
When you shoot under tungsten lights, which have a color temperature of 3,200K, you’ll see the warm, orange/yellow glow of a much warmer light source.
You can see the difference in color temperature in this portrait of songwriter and producer Preston Glass. His face was illuminated by the direct sunlight of the late afternoon sun, which has a slight warm glow to it. The yard that was behind him and served as the background was in shade and had a cooler (bluer) color temperature. This produced an image in which the contrast between the warm and cool light added a nice vibrancy to the image, in addition to reinforcing the color contrast between his skin tone and his hat and jacket.
As you travel through the range of light sources, including fluorescent, halogen, and open shade, you’ll see not only difference in color temperatures, but also, more important, their impact on the rendering of color in your scene.
The good news is that you don’t have to remember these numbers in order to make a good photograph. They’re good to know, but not knowing won’t adversely impact your photographs. What’s important to know is that whichever light source you’re shooting under, if you don’t set the white balance correctly on your camera, your colors may not be as accurate as they could or should be.