Today’s Post by Joe Farace
Light is an interpretive tool in the hands of a photographer. He can make it harsh or soft, revealing or concealing, flattering or libelous. The more he knows about the versatility of light, the easier it is to cope with any picture-taking situation he encounters.”—Peter Gowland
Most of us think about daylight as the proper time for making photographic exposures when photo ops at night, later in the day as well as indoors are often overlooked. They shouldn’t be, but even all colors of daylight are not the same.
You may have heard me say that “Light is light.” That may essentially be true but it’s not always the same color. The color temperature emitted by various light sources is measured in degrees on the Kelvin scale. 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.”
How I made this photo: Photographing in private collections and museums, such as the San Diego Automobile Museum, shown above, can be a challenge because of the kind of mixed lighting conditions that exist. The camera used was a Canon EOS 50D with the wonderfully useful (for photographing cars) EF-S 10-22mm f/3.5-4.5 USM lens at 10mm. Exposure for this photograph of classic Chevy trucks was 1/25 sec at f/3.5 at ISO 400. Understanding the concept behind color temperature and the many options \available to digital photographers—starting with the color temperature options in your camera’s menus—make sure that this white Chevrolet truck is really white in the finished photograph.
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.
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
Joe Farace is co-author along with Pulitzer Prize-winning photographer Barry Staver of “Better Available Light Digital Photography” that includes more information on how some of these images were created. New copies are available from Amazon for $21.50m with used copies are starting around $7.00, as I write this.