White Balance Concepts

Today’s Post by Joe Farace

Most of us think about daylight as the “proper time” for making photographic exposures when photo ops at night or later in the day are often overlooked. They shouldn’t be, but even all colors of daylight are not the same.

You’ve often heard me say “Light is light” but it’s not always the same color. The color temperature emitted by various light sources is measured in degrees on the Kelvin scale. The sun on a clear day at noon is 5500 degrees Kelvin. On an overcast day the color temperature rises to 6700 degrees K, while 9000 degrees K is what you will experience in open shade on a clear day. When we photograph that sunrise, its color temperature may be well down on the Kelvin scale—at about 1800 degrees. Tungsten lights have a temperature of 3200 degrees K, while incandescent light bulbs measure about 2600 degrees Kelvin.

I am constantly amazed at the misinformation I hear about the Kelvin scale. On the Internet, a power company states the “History of Kelvin temperature originally comes from the incandescent lamp.” Duh? Long before Edison and during the nineteenth century Lord Kelvin proposed a new temperature scale suitable for measuring low temperatures, suggesting that absolute zero temperature should be the basis for a new scale. His idea was to eliminate the use of negative values when using either Fahrenheit or Celsius scales. Thus the system is called the Kelvin scale and uses the unit “Kelvin” or sometime just “K.”

Color Temperatures of Common Light Sources

  • Skylight 12000˚to 18000˚K
  • Overcast Sky 7000˚K
  • Average Daylight 5500˚K
  • Electronic Flash 5500˚K
  • White-flame carbon arc 5000˚K
  • 500-watt, 3400 K photo lamp  3400˚K
  • 500-watt, 3200 K tungsten lamp 3200˚K
  • 200-watt light bulb 2980˚K
  • 100-watt light bulb 2900˚K
  • 75-watt light bulb 2820˚K

Photographing in museums, such as the San Diego Automobile Museum, shown above, can be a challenge because of the kind of mixed lighting conditions that exist. Exposure for this photograph of classic Chevy trucks was 1/25 sec at f/3.5 at ISO 400. Understanding the concepts behind White Balance and the many options that are available to digital photographers make sure that this white Chevrolet truck is really white.

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Along with photographer Barry Staver, Joe is co-author of Better Available Light Digital Photography that’s now out-of-print but new copies are available from Amazon for $17.52 or used copies for less than seven bucks, as I write this.