mized in some new lamps, which em- ploy an amalgam principle of mercury vapour control to maintain high light output over a 100-degree temperature span. The amalgam is an alloy of mer- cury and indium that releases more mercury vapour as temperature falls, thereby controlling vapour pressure.
Mercury lamps are almost as effi- cient as fluorescent lamps (about 60 lumens per watt) and somewhat more compact. Colour rendition in general is inferior to incandescent lighting.
J
High-pressure lamps have high effi- ciency for example 120 lumens per watt for the Westinghouse Ceramalux lamp, which provides a rich warm am- ber light that renders colours of build- ing materials well.
Projector lamps are developed for particular needs. A 6-volt 120-watt in- candescent lamp, for example, produces a thin beam that is very effective for lighting tall buildings, columns, steeples, water towers, and the like. Its beam spread of 41⁄2 degrees in one plane by 7 degrees in the other is achieved by masking critical areas of the reflector to prevent refocusing of light.
Flat lighting is uniform illumination of a building. It creates few, highlights
Table 2. Floodlight luminaire types
and shadows and little modeling, but it can be the most economical kind because installation usually is simple and little of the light pattern misses the building. Luminaires can be mount- ed on the ground, on poles, or on the roofs of adjacent buildings or buildings across the street.
Basic effects
Grazing lighting dramatically ex- presses the character of a building by producing strong highlights and sha- dows. It is achieved by mounting flood- lights close to the facade, so it is often lights close to the facade, so it is often used where mounting space is restricted. The best light source for tall buildings is a clear mercury lamp with its arc tube along the axis of a concentrating specular reflector.
Lighting patterns can be used to emphasize or subdue adjacent architec- tural elements, strengthen design con- cepts, or increase the attraction of an otherwise plain surface. The key to success in non-uniform lighting is to create the impression that the effect was planned.
Colour lighting can supplement the increasing use of bold colours in mo- dern construction, both in general
Minimum Efficiency (percent)
Mercury
Incandescent
Fluorescent
Beam Spread (degrees)
NEMA
Effective Reflector Area (sq. in.)
Туре
Under
Over
Under
Over
227
227
227
227 Any
10 to 18
1
34
35
20
18 to 29
2
36
36
22
30
25
29 to 46
3
39
45
24
34
35
46 to 70
4
42
50
35
38
42
70 to 100
5
46
50
38
42
50
100 to 130
6
42
46
55
130 and up
7
46
50 55
Source: National Electrical Manufacturers' Association. Asymmetrical-beam floodlights may be designated by a combination type designation which indicates horizontal and vertical beam spreads in that order; e.g., a floodlight with a horizontal beam spread of 75 degrees (Type 5) and vertical spread of 35 degrees (Type 3) would be designated as a Type 5 x 3 floodlight.
Table 3. Recommended footcandle levels for floodlighting building exteriors
Dark
Footcandles Maintained*
Surrounding Area Bright
Surface Reflectance
Construction Material
Light Marble, White or Cream Terra Cotta, White Plaster
(percent) 70-85
15
5
Concrete, Tinted Stucco, Light Grey and Buff Limestone, Buff Face Brick
45-70
20
10
Medium Grey Limestone, Common
20-45
30
15
Tan Brick, Sandstone
Common Red Brick, Brownstone,
10-20
50
20
Stained Wood Shingles, Dark Grey Brick
Source: Illuminating Engineering Society.
*Light output maintained over the service life of the light source.
floodlighting and as a means of es- tablishing highlights and focal points. It can be achieved either by use of colour filters or by utilizing the in- herent colour differences among the light sources.
Incandescent lighting produces a natural look, mercury lighting tends to cast a slight greenish colour on neutral colours, fluorescent lighting strengthens white or light blue colours, and sodium lighting is rich in amber colour and very effective in adding warmth.
Sparkle or glitter, achieved with ex- posed lamps, also complements modern architecture with its emphasis on line and plane. The lamp size required for a sparkle pattern depends on the bright- ness of the area and the effect desired.
Choosing a luminaire
The first step in determining the type, number, and size of floodlight luminaires required to light a building is to choose a tentative floodlight on the basis of type of light source (in- candescent, fluorescent, mercury, or sodium), shape and size of beam (round or rectangular; wide, medium, or nar- row); and wattage or light output (beam lumens) of the source. As a general rule, if a single requirement must be met, the engineer simply selects the lamp and luminaire best suited for the job. Where there is no clear-cut require- ment, he compares the various lamp and luminaire characteristics and weighs the importance of each.
If more than one light source is suitable, an economic study must be made to determine which would be the best choice for a number of years of service. The comparison of light sources in table can be effectively used as a quick selector.
With the light source chosen, a lu- minaire is selected. Floodlight lumin- aires are usually divided into seven types on the basis of beam spread (table 2). Beam efficiencies (ratio of luminaire output lumens to lamp lu- mens) vary with the type of beam and lamp, as shown.
The second major step in choosing a luminaire is to determine the proper illumination level. A helpful guide is the American Illuminating Engineering Society (IES) recommendations for minimum maintained levels of flood- lighting for various surrounding bright- ness levels and building materials (table 3). If a building is located in an area that is normally crowded, it sometimes is advisable to reduce the brightness on the lower portion of the building to prevent possible annoyance to pedes- trians and motorists.
34
Far East BUILDER, December 1968
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