|Television Production Handbook|
|©1980-2009 Roger Inman & Greg Smith. All rights reserved.|
There are four basic kinds of lights used in television. They are the spot, the broad, the flood, and the soft light.
The spot has a narrow beam that casts well-defined shadows.
The broad is a rectangular light that has a somewhat wider beam and casts softer shadows.
The flood light throws a broad, even illumination in a circular pattern with diffuse shadows.
The soft light (also called a "bathtub") is a array of lights reflected by the white interior of a large box. Used for general background illumination, the bathtub creates shadows that are barely noticeable.
The intensity and beam spread of spots and some other lights may be adjusted by moving the lamp forward or back in the lamp housing. When the beam is narrow and intense the lamp is "spotted down." When the beam is wide and more diffuse the lamp is "flooded out." Not all lamps have this adjustment.
Most lamps can be fitted with "barn doors," which are black metal flaps fastened to the front of the lamp housing. These flaps are used to keep light from falling where it's not wanted. Use of barn doors is most important on backlights, which can cause objectionable lens flare if their light is allowed to strike the camera lens directly.
Scrims are special disks of screen wire which can be used to soften lights and reduce their intensity slightly. Not only can two or more scrims be used in the same lamp to increase the effect, but half scrims or variable density scrims can be used for selective softening of lights. Scrims can also be used in lamps which don't already have protective covers or lenses to contain debris in the event the bulb explodes. Explosions, while rare, are not unknown.
Tungsten-Halogen bulbs are generally used for television lamps. These bulbs retain their brightness and correct color temperature throughout their lives. Unlike household bulbs, however, they can be damaged if touched with fingers (depositing oil on the glass) and are more susceptible to damage by shock. Barring accidents, halogen lamps last from 100 to 300 hours.
Housings may generally be fitted with several different bulbs of different wattages. Acceptable bulb substitutions are often listed on the housing. Bulbs are identified by a three-letter code. Only those bulbs listed should be used in a housing.
Lamps and housing become extremely hot when they're in use. Hot lamps should be handled only with protective gloves to prevent burns.
Television lights are much more powerful than normal incandescent lights. They range from 25 watts for DC camera lights up to as high as 5000 watts. Lights used for electronic news gathering (ENG) or electronic field production (EFP) normally range from 500 to 1000 watts each. This presents problems whenever they're used in locations that weren't intended for television recordings.
The normal utility electrical circuit has a maximum capacity of 15 or 20 amps at approximately 120 volts. One 500 watt lamp uses about 4.55 amps. A 650 watt lamp uses 5.10 amps, and a 1000 watt lamp uses 9.09 amps. To be safe, no circuit should be loaded to more than two thirds of its capacity to prevent overloads from power surges and to allow for possible weaknesses in the circuit. In other words, a maximum of two 500 or 650 watt television lights should be used on a 15 amp circuit.
The above implies that you know which outlets are connected to each circuit, what the rated amperage for each circuit is, and what else is plugged into each circuit.
The formula for finding the amperage for a specific power consumption is:
To be safe, divide the total wattage by 100. This will provide a margin of safety and makes the arithmetic easier.
Any extension cords used with lights should be heavy enough to carry the load. For short distances, number 14 AWG with rubber insulation will carry 15 amps safely. For long runs, it is advisable to use number 12 AWG, which is the same size wire used in household wiring. In addition, grounding wire and circuits should be used where possible.
The formula above has a second use in calculating battery life. If you have a camera light it's most likely a 25 watt quartz light. At twelve volts, a typical one amp hour battery could operate the light for half an hour.