subject: Understanding Color Temperature in Photography [print this page] Understanding Color Temperature in Photography
Introduction:
It would boggle any mind the mathematical calculations of light, color temperature, spectral power distribution and many other scientific calculations which if understood allow us to deliver a great photograph. Lesson one in any photography course is that "Light" writes the photograph. We call it "Painting a Portrait with Light" but it"s all the same. If we need light and light is a complicated mathematical process that we now have to learn then it"s time to learn it.
Lesson Content:
For photographic purposes a preferred method of quantifying the light quality of an incandescent source is by means of its color temperature. Did we just say, "for photographic purposes a preferred method of quantifying the light quality of an incandescent source is by means of its color temperature?"
a. So we are QUANTIFYING the light quality on an incandescent source
Description: Quantify
Description: Incandescent
= (equals) COLOR TEMPERATURE
This is defined in terms of what is called a Planckian radiator, (say what) a full radiator or simply a black body.
This is a source emitting radiation whose SPD (Spectral Power Distribution) depends only on its temperature.
Color temperatures are measured on the thermodynamic or Kelvin scale, which has a unit of temperature interval identical to that of the Celsius scale (Do you even know what a Celsius scale is?) but with its zero at -273.15 C.
I know, I know, most artists are not mathematicians. This type of information can be overwhelming at first. But you're a bright person, a bright apple right? Proceed slowly and re-read the information and you'll get it down, I guarantee you will.
The idea of color temperature can be appreciated by considering the progressive change in color of the light emitted by a piece of metal as its temperature is raised, going from dull black through red and orange to white heat. The quality of the light emitted depends on the temperature of the metal.
Luminous sources of low color temperature have an SPD relatively rich in red radiation. With progression up the color scale the emission of energy is more balanced and the light becomes whiter.
At high values the SPD is rich in blue radiation. It is unfortunate that reddish light has been traditionally known as warm and bluish light as cold, as the actual temperatures associated with these colors are the other way round.
The idea of color temperature is strictly applicable only to sources that are full radiators, but in practice it is extended to those that have an SPD approximating to that of a full radiator or quasi- Planckian source, such as a tungsten-filament lamp. The term is, however, often applied incorrectly to fluorescent lamps, whose spectra and photographic effects can be very different from those of full radiators. The preferred term describing such sources is correlated color temperature, which indicates a visual similarity to a value on the color temperature scale (but with an unpredictable photographic effect, particularly with color reversal film). I know it may be painful to read this type of techno-mumbo but once you learn the math it"s as simple as perfecting your art.
In black-and-white photography, the color quality of light is of limited practical importance. In color photography, however, it is vitally important, because color materials and focal plane arrays (FPA) are balanced to give correct rendering with an illuminant of a particular color temperature. Consequently, the measurement and control of color temperature must be considered for such work, or the response of the sensor adjusted, usually termed white balance
