LIGHTING After installing the switches needed to control the lighting, you need to mount the light fixture itself. Each lighting installation is designed to produce a specific level of illumination adequate for those working in the area. The amount of illumination initially provided starts to decline almost as soon as it is put in operation. This reduction is caused by dirt on the lamps and luminaries, a decrease in lamp lumen output, and dirt on the room walls and ceilings. Illumination should be sufficient to eliminate eyestrain, support a high level of production, and promote safety and employee morale.

Lighting fixtures are designed for a particular lamp size and type. Many fixtures, however, were installed in military buildings long before the manufacturers started producing higher and higher wattage lamps in ever smaller envelopes. Consequently, it is possible to use much higher wattage lamps than the fixture or the circuit can handle adequately.

CAUTION Excessive heat of higher wattage lamps can damage the sockets, increase failure rate, and overload the circuits. Personnel are cautioned to use only the lamp size (in watts) recommended for the fixture, rather than a higher wattage lamp that may physically fit.

INCANDESCENT LAMPS Incandescent lamps come in a variety of voltage ratings. For most applications, the lamp voltage rating nearest the available line voltage should be selected. Under this condition, the lamp will produce its rated values of life, watts, and light output. Many incandescent lamps are available with life ratings considerably in excess of ordinary general service lamps. Some have ratings of 5,000 hours or more, and some even are guaranteed to burn for 5 years. General use of these lamps is not recommended because the initial cost is comparatively high and the extended life is gained by reducing the light output. There are, however, a few areas where it is necessary to use bulbs with a long life. Typical locations include high-ceiling auditoriums, exit lights, stairwells, and marker lights on towers or fire alarm boxes. For these areas, do not use a special rated lamp. Do use an ordinary general service lamp whose voltage rating is higher than the circuit voltage; for example, 130-volt or higher lamps for 120-volt circuits. When you are operating the lamp below its rated voltage, the life is increased at a sacrifice in light output. For general use, the lamp voltage rating nearest the available line voltage should be used.

Many kinds of incandescent lamps are especially designed for placement in a variety of situations; for example, under severe physical conditions (such as vibration or extreme temperatures), in inaccessible locations, or when special lighting effects are desired. Some of these types of incandescent lamps and their uses are as follows:

INSIDE-FROSTED LAMPS are used in most fixtures designed for incandescent lamps. The frosted finish reduces lamp brightness and glare. 

CLEAR LAMPS are used in fixtures where control of the light is required (such as in reflectors having polished reflecting surfaces and in enclosed globes or reflectors of prismatic glass), particularly where concentrated light control is required, as in high, narrow bays.

Reflector equipment of the diffusing globe type, where the lamp protrudes through the bottom of the fixture, requires WHITE BOWL LAMPS. The white bowl reduces the surface brightness and glare from the working surfaces.

SILVERED-BOWL LAMPS are used principally for indirect lighting and in reflector equipment. The fixture parts should not touch the lamp as the thermal expansion may cause the bulb to crack and fail prematurely.

REFLECTOR LAMPS with the reflecting surface inside the lamp are, in effect, a fixture in themselves. A collection of dust and dirt on the exterior of the lamps can cause them to lose their effectiveness.

PROJECTOR LAMPS are installed in indoor and outdoor display lighting fixtures. They use a self-contained reflector but have an advantage over the reflector type since they are suitable for extreme temperature conditions and provide more accurate light control.

HEAT AND DRYING LAMPS, available with built-in reflectors or with separate reflectors, are an inexpensive answer to a requirement for instantaneous infrared energy. The reflector bulb keeps the initial cost to a minimum and provides a new reflecting surface with each new lamp.

HARD-GLASS LAMPS, made of special glass with high resistance to thermal shock, are effective where rain, splashing liquids, insects, snow, fixture parts, or hot metallic spray may touch the glass bulbs.

VIBRATION SERVICE LAMPS are available that withstand excessive vibration that cannot be eliminated by flexible fixture mounting. Where the lamp will be subjected to shock, such as at the end of a drop cord or near machinery, you will want to select ROUGH SERVICE LAMPS. With filament supports, these lamps can withstand severe shocks without failure. High-cost replacement areas, such as towers, industrial high bays, theater marquees, halls, and stairwells, are lighted with LONG-LIFE LAMPS.

QUARTZ-IODINE LAMPS offer a concentrated source of incandescent light with excellent light control characteristics, good color, and a life twice that of regular general service incandescent lamps. They depreciate at a lower rate than the general service lamp. The lamp cost is considerably higher, however, than a general service lamp, and a special fixture is required.

FLUORESCENT LAMPS There are two principal types of fluorescent lamps: instant-start and rapid-start preheat lamps. Both have practically the same physical dimensions but different internal construction. The type of circuit in which the lamp should be used is etched on the end of the lamp. The rapid-start preheat lamp operates satisfactorily with either the preheat or rapid-start circuits. It has a short lamp life in an instant-start circuit. The instant-start lamp operates satisfactorily with an instant-start ballast, burns out the ballast in a rapid-start circuit, and does not light in a preheat circuit. Preheat lamps dominated the field for many years but are no longer considered a major type. They continue to be in use, however, particularly in fixtures using lamps smaller than 40 watts. Examples of circuits for the major types are readily found in current manufacturers' publications. Example of some circuits are shown in figure 5-76. The 4-foot rapid-start lamp is the preferred lamp for most applications.

Figure 5-76.- Representative fluorescent circuits.

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(c) 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.