AREA LIGHTING SYSTEMS This section covers streetlighting, floodlighting, and security lighting systems. When properly constructed and installed, these original basewide lighting systems will provide years of trouble-free operation with a minimum of minor maintenance and bulb changing required to keep the system fully operational.

Several factors can change the base requirements for area lighting. These factors include such changes as facility usage, updating of systems, changes in the base mission, or expanding existing systems.

With the cost of energy rising daily, any system that can provide a higher level of efficiency for the energy used must be considered. The use of the newer high-

pressure discharge systems for lighting seems to offer savings both in the lifespan of the bulbs and in the lumens per watt of energy used These systems are replacing the older incandescent systems in an ever-increasing pace. The higher initial cost of these systems is being offset by the efficiency of the energy used and savings of energy dollars.

TERMINOLOGY AND DEFINITIONS You will need an understanding of lighting techniques and effects to understand the physical concepts and terminology involved in lighting systems.

We will use both the American Standard (AS) and the metric system (SI) when discussing lighting concepts. The AS standards will be without brackets, whereas the SI terms will be noted in square brackets [ ].

The candlepower [candela], abbreviated cp [cd], is the unit of luminous intensity. It is comparable to the voltage in an electrical circuit and represents the force that generates the light you can see. An ordinary wax candle has a luminous intensity of approximately one

Figure 6-12.- Basic passive fiber-optic coupler design.

candlepower [candela], hence the name (fig. 6-13). A candle radiates light equally in all directions. If you imagine such a source surrounded by a transparent sphere of one foot [meter] radius (figure) than by definition, the amount of luminous energy (flux) emanating from one square foot [meter] of surface on the sphere is one lumen [lumen], abbreviated lm.

Since there are 40 square feet [meters] of surface area in such a sphere, it follows that a source of one candlepower [candela] intensity produces 40 or 12.57 lm (a lumen is a unit of light quantity), and in terms of power is equal to 0.0015 watt. It therefore also follows that 1-cp [cd] source produces 12.57 times 0.0015 watt; that is, 0.0189 watt or approximately 1/ 50 watt of luminous energy. The lumen, as luminous flux, or quantity of light, is comparable to the flow of current in an electrical circuit One lumen of luminous energy occurrence on one square foot of area produces an illumination of one footcandle (fc). When the area is expressed in square meters, the illumination is expressed in lux (lx). If you were to consider a light bulb to be comparable to a sprinkler head, then the amount of water released would be the lumens and the amount of water per square foot (meter) of floor area would be the footcandles [lux]. The metric unit, lux, is smaller than the corresponding order to change footcandle to lux, you would multiply by 10.764.

Restating what you have just learned mathematically, it would look like this:

footcandles = lumens square feet of area

Or lux= lumens square meter of area

High Intensity Discharge Lighting Efforts to improve the power efficiency and reduce the maintenance costs led to the development of a new family of lighting that has been generally categorized as high--intensity-discharge lamps (HID). These lamps all have a negative-resistance characteristic. This means that the resistance decreases as the lamps heat up.

As the resistance decreases, the current increases. In fact, the current will increase indefinitely unless a current--limiting device is provided. All gaseous conduction HID lamps, therefore, have current limiters, called "ballasts." Lamp life and more light per watt are two main advantages that HID lamps have over incandescent bulbs. The basic types of HID lamps used unit, footcandles, by a ratio of approximately 10 to 1. In in area lighting consist of three groups of lamps:

Figure 6-13.- Relationship between a light source of one candlepower and the illumination produced.

mercury lamps, metal halide lamps, and high-pressure sodium lamps. All high-intensity-discharge lamps produce light from an arc tube that is usually contained in an outer glass bulb.

Figure 6-14 shows the basic configuration of a HID lamp. In these lamps, a material, such as sodium, mercury, or metal halide, is added to the arc tube. In design, the lamp has three electrodes- one acting as a cathode and the other as an anode with the other electrode being used for starting. The arc tube contains small amounts of pure argon gas, halide salts, sodium, and vapor to aid in starting. Free electrons are accelerated by the starting voltage. In this state of acceleration, these electrons strike atoms and displace other electrons from their normal atomic positions.

Once the discharge begins, the enclosed arc becomes the light source.

Commercial companies that produce these light bulbs claim a 100-percent increase in lamp life over tungsten filament bulbs that produce the same amount of light. The power in watts required to operate these lamps is less than one half of that required for filament lamps. The initial cost of the components for lights is

Figure 6-14.- HID lamp configuration.

substantially greater as these lights will require ballasts; however, this cost can be made up later by the savings of energy costs. The selection of lighting fixtures will

depend on budgeted dollars for new installation projects versus maintenance dollars.

Most discharge lighting fixtures are supplied with the required ballast installed in the fixture. In some cases ballasts, usually called transformers, are externally installed.