5. Color temperature is the standard presently used in television to measure
the relative reddishness and bluishness of "white" light. A fluorescent bulb
actually emits a blue-green tint while a candle emits a reddish tint.
This
difference can be measured precisely and expressed in degrees kelvin.
Lord
Kelvin devised this scale by heating a carbon filament, which he considered to
be completely light absorbing and therefore a black body, from absolute zero to
various degrees centigrade. He observed that the hotter the black body got,
the more bluish the emitted light became. Conversely, the more the temperature
dropped, the more reddish the light became. If he heated the filament to 3200K
(3200 degrees from absolute zero centigrade) it emitted a fairly white light.
Therefore, we consider 3200K the standard for "white" indoor light.
a. Outdoor illumination is bluer than indoor light and, therefore, has a
different color temperature. The standard color temperature outdoors is about
5600K as measured on a midsummer day at high noon in Washington, DC.
b. Most studio lighting instruments are rated as 3200K, assuming they
receive full voltage.
Lighting instruments that are used to simulate or
augment outdoor illumination have bulbs that are rated at 5600K.
We will
discuss these lighting instruments in more detail in a later section of this
subcourse.
6.
Technical lighting requirements are to provide enough light so that the
camera can "see well" and to limit the contrast between highlight and shadow
areas. In order to understand technical requirements, it is necessary to break
them down into two separate areas, operating light level (base light), and
contrast.
a. In order to make the camera see well, that is, so the pictures are
relatively free of video noise and lag, a minimum operating light, called base
light, must be established. Base light is the overall light level on a set or
event area.
(1) Base light can be achieved in two distinctly different ways. The
first method is to establish a highly diffused illumination through the use of
floodlights.
The specific areas requiring lighting (people, specific set
areas, etc.) could then be added to the base lighting.
(2) The second and most preferred method is to light those areas
requiring specific lighting first, then fill in the harsh shadow areas with
floodlights.
By using this method, very little additional light will be
required to meet the base light requirements.
(3) On remote productions, where time and lighting equipment are
limited, using the first method of establishing base light is the more
practical of the two.
(4) The level of intensity required for proper base light varies with
the type of camera used. However, if 250-foot candles are used as a standard
light intensity level, practically any camera on the market today will function
properly.
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