![]() The former determines the area covered by the beam and the latter the illumination provided. Two considerations enter into the choice of a projector, viz., beam size and light output. The illumination level (lumens/m) required depends upon the type of building, the purpose of the floodlighting, the amount of conflicting light in the vicinity etc. The problem of flood-lighting calculations may be roughly separated into three steps. Projectors are classified according to the beam spread: In some cases the projectors may be housed in ornamental stand standards. As far as possible the projectors should not be visible to the passers-by. ![]() ![]() The front of the projector is usually of clear glass, often bowed outwards to protect it from the heat of the lamp use of diffusing glass is made when a diffuse beam is required. This may be achieved by providing sufficient radiating surface. When 500 or 1,000 watt lamps are used in projectors, ventilation may have to be provided for adequate cooling. For permanent installations use of cast-metal cases is made to achieve robustness and protection against weather and for temporary installations or those in sheltered situations, use of sheet metal casing is made. The casing and its mounting are arranged so that the inclination of the beam can be varied in both a vertical and a horizontal direction on site. Metal reflectors being more robust are usually preferred. This may be made of silvered glass or chromium plate or stainless steel the efficiency of silvered glass is about 90% while that of polished metal is only about 70%. The reflecting surface is the most important part in a projector. Since it is usually installed in remote positions, therefore, it must be robust and weatherproof in construction. The particular type of reflector and its housing used for concentrating the light into narrow beam is known as floodlight projector. For floodlighting it is necessary to concentrate the light from the light source into a relatively narrow beam.
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