Fluorescent Lighting

Fluorescent lamps of high-pressure, hard glass are now being used to some extent for floodlighting where a low-level, highly diffused light is desired. This would include club parking lots, outside shopping areas, parks, or grass areas. This bulb is much the same in operation as the mercury-vapor lamp with the exception that the fluorescent tube has an inside coating of material called phosphor that gives off light when bombarded by electrons. In this case, the visible light is a secondary effect of current flow through the lamp. As with other electric-discharge lamps, the fluorescent lamp requires a ballast for operation. The color produced by the light depends on the phosphor material used.

Luminaire Ballasts

Every electric-discharge lamp needs a ballast to operate. The ballast is simply a coil of insulated wire wound on a frame, or a laminated iron core.

Ballasts may perform any or all of the following functions:

Limit the current flow through the lamp to the value for which the lamp is designed.

Cause a drop in line voltage and provide the desired lamp voltage, which, in turn, determines the rated current in the lamp.

Provide power factor correction.

Provide radio interference suppression.

The ballast core is made of laminated transformer steel wound with copper or aluminum magnet wire. The assembly is impregnated with insulating material that provides electrical insulation while aiding in heat dissipation and, with leads attached, is placed into a case. The case is filled with a potting material containing a filler, such as silica. This compound completely fills the case encapsulating the core, coil, and capacitor.

Average ballast life at a 50-percent duty cycle and at proper ballast operating temperature is normally estimated at about 12 years. At higher ballast temperature or longer duty cycle, shorter ballast life will result.

According to the National Electrical Code^R, (NECR)1, Article 410-73e, it is mandatory that all fluorescent lamp ballasts used indoors be internally protected and that replacements for these ballasts be integrally protected. These protective measures were taken to prevent misapplication of the ballast as well as to protect against undesirable failure and conditions which can occur at the end of ballast life. The thermally protected Underwriters' Laboratories approved ballast is known and marked, or labeled, as "Class P."

The operating characteristics of the ballast may result in a low- or high-power factor. The measured watts of a low-power-factor ballast are approximately the same as the measured watts of the high-power-factor ballast when they are connected to the same load. The low-power-factor ballast draws more current from the power supply, and therefore, larger supply conductors may be necessary. The high-power-factor ballast permits greater loads to be carried by the existing wiring system.

Fixtures

There are fixture configurations to meet almost any lighting requirement or design. While the basic purpose of the fixture is to hold and prevent damage to the lamps and lamp sockets,

¹ National Electrical Code^R and NEC^R are registered trademarks of the National Fire Protection Association, Inc., Quincy, MA.

the fixture also helps direct the light beams into the lighting patterns desired. The fixture, with its reflector and lens, determines the quality of the light being produced. Reflectors can either concentrate or diffuse light rays, and the lens can pass or refract light rays. Quite often, the lens may be used to do both from one light source; that is, part of the light rays are refracted to produce a soft, even spread of light in the outer part, while the light rays are concentrated in other areas of the lens to produce a bright, hard light at a specific area. Some streetlight fixtures are examples of this. The sides of the lenses produce a general diffused lighting to prevent blinding automobile operators while, at the same time, they produce a bright light pattern below the lamp along the curb.

Flood or security lighting fixtures may be either open or enclosed. The open fixtures provide higher maintained efficiency and more accurate beam control. The open fixture will, under some conditions, require a "hard glass" bulb to prevent bulb breakage caused by rain, snow, or insects striking the hot bulb.

Most fixtures will have provisions for mounting ballasts (transformers) within the fixture and will provide protection for the ballast. In some cases, particularly in high bay lighting, the ballasts may be mounted at some central location and not mounted in the fixture. Figure 1-2 shows representative samples of the styles of fixtures

Figure 1-2.\Fixture styles available.

available. In the pole-mounted group, the ballasts are located in the pole base. Several methods of fixture attachment are possible and should be considered when fixtures for a particular job are ordered. The location and job determine whether the fixture is suspended, bracket mounted, or arm mounted. Most brackets can be attached either to wood or metal support structures. In either case, the fixture should be firmly attached to the structure so that precise aiming for light distribution can be made.

LIGHT CIRCUITS

As we stated earlier, a number of light systems are in use today, such as streetlights, floodlights, and security lights. These systems are either series or multiple (parallel), depending on how they are used and the equipment available.

The series circuit is supplied by a regulating transformer which gives a constant current, usually of 6.6 amperes, to the lighting circuit. If a higher amperage is required, *autotransformers are available for stepping up the current to 15 or 20 amperes. This higher amperage permits the use of more rugged lamp filaments, which give longer life for lamps of equal candlepower and higher lamp efficiency.

The series circuit is easily controlled, but any break interrupts the entire circuit. The use of film-disk cutouts (fig. 1-3) in the lamp socket

Figure 1-3.\Series lamp, socket, and film disk.

prevents lamp failure from interrupting the circuit.

The multiple (parallel) circuit consists of a number of streetlights supplied by a distribution transformer delivering a constant low voltage to a circuit or secondary main which also supplies other loads. However, running secondary conductors any great distance to supply a parallelconnected lamp or a group of lamps is impractical because of the excessive voltage drop.

The cost of the multiple luminaire is low compared to the series type because the low voltage allows for the elimination of other luminaire accessories. This saving is largely offset, however, by the increased requirement for control devices and the copper wire cost. Lamp life and efficiency are comparatively low and the illumination is not as uniform as in the series circuit.

In choosing a system, here are a few suggestions which may aid in your selection.

If the total wattage of the circuit exceeds 2 kilowatts or more than 15 lights, consider a series lighting system.

When extending an existing system, use the existing circuit.

If low-voltage capacity exists at the proposed location, use a multiple system even though the load exceeds 2 kilowatts.

When several small lights are to be spaced rather far apart and no low-voltage secondary exists along the route, use the series system regardless of the load size or the number of lights.

When estimates show that one type of system will save money and time, use the more economical system.