The third step is to estimate the coefficient of beam utilization (CBU), which is the ratio of lumens striking the floodlighted surface to beam lu- mens. The area to be flooded is super- imposed on the photometric grid of the luminaire chosen, and the ratio of lumens inside the area to total beam lumens is calculated. A typical CBU value is 75 to 80 per cent if the unit is properly chosen. If the value is below 60 per cent, a more economical light- ing plan probably can be devised by using different floodlight locations or luminaires with narrower beams.
The next step is to calculate the number of luminaires required:
Number of luminaires =
A x FC
BLXCBUXMF
where A is area of the surface to be lighted by the footcandles (FC) desired, BL is beam lumens of the unit, and MF is maintenance factor of the lumin- aire. Maintenance factor depends on type of luminaire, location, and main- tenance practices; it is typically 70 to 80 per cent for enclosed units and 85 per cent for projector and reflector lamps.
The last step is a geometric check to make sure that the luminaires chosen will cover the surface smoothly. Gen- erally, each beam pattern should be overlapped completely by those on either side (unless pattern lighting is desired). If coverage is not complete, the engineer applies a larger number of lower-wattage units or wider-beam units and recalculates.
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Government House, Hong Kong, floodlit by 76 tungsten lamps
A fine example of modern flood- lighting practice is the Pan Am Build- lighting practice is the Pan Am Build- ing, New York, which is lighted from the tenth floor setback up to the top of the 59th floor, a distance of 550 ft. (fig. 1). To achieve such lighting, special searchlight type luminaires were de- veloped. The lamp had to have the most compact filament possible to en- able the luminaire mirrors to project narrow but intense beams to the top of the building.
At the same time, enough spread was needed to enable the luminaires to cover the lower areas, and burning
Near-distance tungsten lamps placed behind the colonnades of the Supreme Court Building, Hong Kong, and directed against the facades of the building effectively silhouette the columns and ballustrades
life of more than a year was desired. The lamp that was developed has a globular bulb of hard glass 8 in. in diameter and a special 80-volt filament operating at 2,000 watts.
A collector grid traps tungsten par- ticles as the filament vaporizes, pre- venting bulb blackening and thereby assuring good lumen maintenance. The special luminaires have cast aluminum housings with mirrored glass reflectors and clear tempered lenses. Each of the 170 units produces 2,750,000 candelas.
The smaller faces of the building are floodlit with 1,000-watt quartz- iodine lamps in luminaires that supply the same light distribution provided by the searchlights on the larger sides. Al- together, the luminaires wash the build- ing with some 376 kW of lighting.
In Hong Kong a well-known land- mark which is effectively floodlit at night is the Government House. Its spacious grounds allow the sighting of long, medium and near-distance lamps to evenly distinguish the white walls and tower.
Seventy-six G.E.C. tungsten lamps are used for this installation. There are 12 FF69020 Dover 1,000-watt conve mirror long-distance lamps, 27 F69038 Singapore 1,000-watt plain-glass me 1- ium distance lamps, and 37 F69023 plain-glass lamps of 500 to 1,000 watts for near distances.
Acknowledgement
This feature is based on a paper prepared by Mr. K. Chen, Facilities Department Lamp Division, and Mr. E.B. Karns, product com- munications manager, Lighting Division, Wes- tinghouse Electric Corporation.
Far East BUILDER, December 1968
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