c. The second curve shows the relative energy from a typical
incandescent light source. Most of its energy falls in the red region 6000
to 8000 angstrons.
For this reason incandescent lamps appear yellow or
slightly red to any light source, determined by the relative sensitivity of
the human eye as represented by the third curve in figure 6-1.
2.
We know that both the plumbicon and the vidicon camera tubes have
response curves closely resembling the sensitivity curve of the eye.
Although both tubes perform satisfactorily as pickup tubes, they are
sensitive to light levels. The spectrum of light is good for both, however,
the plumbicon lighting level for producing good pictures lies between 32 and
64 footcandles with an f:8 lens.
The average TV installation should be
capable of producing 200 footcandles of illumination on any given scene, to
permit flexibility in the control of lighting and lens stops.
3.
Again referring to figure 6-1, you can see that where the energy of
the incandescent lamp is weakest, the sensitivity of the eye is strongest.
Since the sensitivity of the camera tubes and the eye compare favorably, you
can assume that the incandescent lamp is a good light source for TV.
Fluorescent lighting is weak in the red region and, therefore, skintones
appear darker.
4.
It is for this reason that fill light or key light of an incandescent
source must be used with fluorescent lighting.
This knowledge of proper
lighting techniques is important to the maintenance man for making proper
camera adjustments.
5.
Incandescent lamps provide good control of the beam pattern and
intensity of the lighting.
The lamps are easy to dim and very easy to
handle and manipulate.
The good color output of incandescent lamps is
desirable for both monochrome and color applications.
6.
A special type of incandescent lamp developed in recent years is
tungsten-halogen, or quartz. You should use this lamp where color cameras
are used. Characteristics which make it desirable are:
a. Constant lumen output throughout life.
b. Constant color temperature throughout life.
c. Color temperature output that matches the design center for color
cameras, normally 3200 kelvin.
d. Increased life over conventional incandescent lamps for equal lumen
output and color temperature.
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