b. What Color Temperature Is.
Notice that color temperature refers
only to the visual appearance of the light source, not to its photographic
characteristics.
(1) For example, fluorescent and tungsten lamps may present a visual
match but the photographic results differ appreciably. Color temperature is
most reliable when used to describe the spectral quality of tungsten light
sources.
(2) The spectral quality of a light source is related to its Kelvin
temperature.
Incandescent lamps produce light when electrical current
passes through a thin filament to glow.
(a) The hotter the filament becomes, the brighter the light.
With
the increase in temperature, there is a change of color quality.
(b) At lower incandescent temperatures, the filament glows red, as
the temperature rises, the color changes to orange and yellow hues then
finally to white. Thus, you can see color is related to temperature.
8.
Undesirable Radiations.
Some radiations produce undesirable effects in photographic emulsions.
These radiations are ultraviolet, infrared, gamma, and X-rays. The results
can range from a completely unusable photographic image to minor losses in
image definition.
a. Ultraviolet. Ultraviolet radiation and some visible blue light, if
scattered by the atmosphere, can result in a loss of image definition. This
scattering, caused by moisture and other airborne particles, is called haze.
Light scatter may restrict the exposing of color materials during the early
morning and late afternoon. Light scatter can become objectionable when it
causes undesirable shifts in color balance.
b. Infrared. Infrared is always associated with heat. This heat has
an adverse effect on the stability of the dyes used in color materials. At
3000K, three-fourths of the radiation emitted by a tungsten lamp is
infrared. Color printing enlargers, using tungsten lamps as light sources,
employ heat-absorbing filters to prevent damage to the negative during
printing.
Heat also can cause significant increases in the fog level of
photographic materials. You must consider this factor when you store color
materials for any length of time.
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SS0514
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