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1949 TELEVISION STUDIO LIGHTING 621
to hang most of our lighting equipment from overhead where it is out of the way of scenery, props, cameras, and personnel.
It will be apparent from the foregoing that a considerable amount of power is required for lighting. It is considerable, but not nearly so bad as in the days before the image-orthicon tube. With imageorthicon cameras and approximately half of the lighting units of the fluorescent type, we come out with a requirement of about 25 kilowatts connected load for a small studio of the order of 25 by 30 feet. For a large studio, perhaps 40 by 60 feet, the connected load would probably be around 60 kilowatts. A good rule-of-thumb for estimating lighting power is about 30 watts per square foot of floor area in the studio.
One should distinguish between "connected load" and actual load at any one time. It will be understood from preceding references to preset lighting that all the lighting units are never expected to be used at one time. The broadcast operator would probably not use more than 25 or 30 per cent of the units at any one time. The electrical codes will not permit one to economize on wire, conduit switches, and fuses on the basis of this probability. However, a real saving can be effected in air-conditioning facilities by taking account of this partial usage of lighting facilities.
There are a few incidental points that must be taken into account in any good studio lighting installation. Mention has been made of the need for quietness in operation. The devices shown for tilting and turning the lighting fixtures meet the requirements of silence in movement. Quiet operation of switching is also necessary. Snapaction switches cannot be tolerated in the studio. For small installations there is a silent toggle switch with mercury contacts. For a little larger installation there is a mercury-contact relay whose coil circuit can be switched with the silent toggle switches. For the largest installations a separate relay room is worth while. Then it does not matter how noisy the relays may be and their coils can be operated with push buttons in the studio.
Some fluorescent-lamp ballasts develop an objectionable hum. These cannot be tolerated in the studio. A lot of wiring can be saved if the ballasts are near the lighting units. Therefore, it is wise to select good quiet operating ballasts and mount them so that hum vibration cannot get into the fixtures or supporting grid where it can radiate noise. These points are given due consideration in the manufacture of lighting units shown in the accompanying illustrations.