82 Better Available Light Digital Photography
Light is light?
Light may be 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. (See “Who Is This Kelvin Guy?”)
The sun on a clear day at noon is 5500 K. On an overcast day,
the color temperature of light rises to 6700 K. You will experi-
ence 9000 K in open shade on a clear day. When we photograph
that special sunrise, its color temperature may be well down on
the Kelvin scale—to about 1800 K. Lights used by videogra-
phers or tungsten light lightbulbs used in so-called “hot lights”
have a Kelvin temperature of 3200 K. The light from household
lamps is close to that color temperature, measuring about
2600 K.
One of the toughest light sources to Color Balance is fl uorescent.
The type and age of each tube in a fi xture affect color and fi lm
cameras usually require special fi ltration to produce an image
that looks neutral. Filters may be helpful in correcting the light’s
color, but they also darken the viewfi nder, making it harder to
focus and compose the image, and they increase exposure time.
With digital cameras, all that’s changed.Photographing in museums, such
as the San Diego Automotive
Museum, can be a challenge
because of the kind of mixed-
lighting conditions that exist.
Exposure was 1/15 sec at f/4.5 at
ISO 400. Understanding the con-
cepts behind White Balance and
the many options that are avail-
able to digital photographers
make sure that this white vintage
Indy racer is really white. That’s
what this chapter is all about. ©
2006 Joe Farace.
Who Is This Kelvin Guy?
I am constantly amazed at the misinformation I hear about the Kelvin scale. On the Internet, a power company
states that the “History of Kelvin temperature originally comes from the incandescent lamp.” Duh? Long before
Edison invented the incandescent light, William Thomson (Lord Kelvin), an Englishman, proposed a new
temperature scale suitable for measuring low temperatures. During the 19th century, he suggested that absolute
zero should be the basis for a new scale. His idea was to eliminate the use of negative values that occurred when
measuring low temperatures using either Fahrenheit or Celsius scales. In honor of Lord Kelvin’s contributions,
this system is called the Kelvin scale and uses the unit “kelvin” (lowercase), which is abbreviated “K” and is used
without the degree symbol or the word “degrees.” Another unit of color that you might see occasionally is the
mired (micro reciprocal degrees), which is a unit of measurement equal to 1 million divided by the color
temperature, and is used to indicate color-correcting fi lter densities.