Fluorescent lamps are available in a variety of colors for decorative use as well as numerous shades of white for general illumination. The predominant white shade recommended for most office areas is cool white. Other shades of white used for various purposes include daylight, deluxe cool white, white, warm white, and deluxe warm white. Daylight and cool white provide a crisp, cool, businesslike atmosphere, and the warm whites find application in restaurants, homes, theaters, and similar areas. The appearance of colored materials will be better under a fluorescent light that contains a high component of the same color. Blue backgrounds improve with the cool whites and daylight. Deluxe warm whites strengthen oranges and yellows.
Fluorescent lamps require ballasts to limit the current and to supply proper voltage to start and to operate the lamps. For general lighting purposes, the ballasts also contain a capacitor to improve power factor. The NEC requires that all indoor fluorescent fixtures (except those with simple reactance ballasts) incorporate ballasts with thermal protection. The thermal protector isolates the ballast and fixture from the circuit in the event of overheating. As a result, damage from fires and from leaking compounds should be reduced. There are small fuses available that can be installed in the fixture to provide this protection for existing ballasts.
Mercury lamps (fig. 5-77) have the best maintained light output because the electrodes operate at a relatively cool temperature, resulting in less evaporation of the metals and oxides. The clear mercury lamp has a better lumen maintenance than those with phosphor coating. Long average life (16,000 hours and up) is a primary characteristic of most mercury lamps. There will be a different economic life for mercury lamps at each installation, depending on lamp mortality, power cost, equipment and wiring costs, frequency of replacement and cleaning of lamps, and other factors. Mercury lighting is one of the most economical means of lighting high- and medium-bay industrial areas, particularly in areas where color rendition is not critical. Small wattage lamps have been introduced, and it is anticipated that future designs will see a more widespread use of these in low-ceiling nonindustrial areas. An objectionable characteristic of mercury lamps is the time required to reignite (several minutes) after a momentary loss of power.
CAUTION While the lamp bases are the same size as incandescent lamps, mercury lamps must never be used to replace a burned-out incandescent lamp because a ballast must be used with mercury lamps.
Metallic-vapor lamps resemble mercury-vapor lamps in appearance and have similar uses. The initial efficiency and control are better with metallic-vapor lamps than with mercury-vapor lamps. In regard to disadvantages, the rate of depreciation is much greater with metallic than with mercury, the cost is higher, and the life expectancy is shorter.
High-pressure sodium-vapor lamps are used for highway interchanges, parking lots, and high-bay industrial areas. They are the most efficient of the light sources in general use in number of lumens produced per watt of electricity. The relative cost is high, the life ratings are not well established, and a special ballast is required. The color is slightly yellowish
Walls, ceilings, and surroundings are an important part of the overall illumination system since they redirect light to the working area. The most efficient lighting system is obtained when the fixtures are new and when the walls, ceilings, floors, and furnishings of
Figure 5-77. - Mercury lamp.Continue Reading