Any commercial lighting project for a typical mall, or atrium, starts with selection of the lamps, or light sources.
Most property owners prefer to use as few lamp types as possible to reduce maintenance and stocking costs. Four or five lamp types is a good compromise in most cases, but most lighting designers try to stay with one lamp wattage for each major type specified.
In specifying the stable of lamps, consider using the following products: HID lamps (metal halide is the only real choice), fluorescent lamps (today's popular T8 model), PAR halogen lamps, compact fluorescent sources, and one or two incandescent lamps for accent or sparkle.
Energizing the metal halide lamp The metal halide (MH) light source is an excellent choice for providing the ambient, or general lighting level in a shopping plaza. The layout of such lamps should produce 20-fc horizontal, or less, of illumination. New, low-wattage MH lamps can be applied in ceilings as low as 9 ft. For example, many designers now use MH lamps of 175-W to 250-W ratings to handle general down lighting from high ceilings. This method excludes using a high-wattage light source that could cause distracting glare to shoppers circulating through the area.
The single-ended MH lamp is available in a standard universal burning line, a standard position-restricted line, a safety line, and a special shrouded arc tube line. Standard universal burning lamps, the most widely used type, can be operated in any burning position from base-up to base-down. They are available in clear and phosphor-coated versions, in both mogul and medium-base designs.
Standard position-restricted lamps provide optimum output because of the construction of their arc tubes. When a universal-burning, straight-arc-tube MH lamp is burned horizontally, its arc tends to bow upward because of convection currents; thus, a lamp having an arc tube bent in conformity to this natural bowing process would be position restricted.
The lumen output of a bent-arc-tube lamp is considerably higher than a horizontally burning, straight-arc-tube lamp of the same wattage. The safety-line MH lamp uses a method of disconnecting the power to the arc tube if the outer bulb is broken or shattered. This lamp type is recommended for use in open bottom fixtures. The shrouded arc tube line of MH lamps is for use in open fixtures where increased fixture efficiency and lower maintenance costs are important. Basically, the shroud is a glass cylinder that surrounds the arc tube. Should ballast fragments be discharged from a ruptured arc tube (at the end of lamp life), they will be blocked from hitting the outer glass bulb and shattering it.
Also consider the new high-efficiency 350-W MH lamp that delivers 44,000 lumens compared to 36,000 lumens produced by a standard 400-W lamp and the 40,000 lumens of a high output 400/BU (base up) lamp. The lamp has wide application, particularly as replacement for a line of lower wattage lamps in the 100-W to 400-W range.
The 350-W MH lamp's unique body arc tube also contributes to faster restart time. A standard pinched-body arc tube typically uses a secondary smaller electrode in one end of the arc tube. This starter electrode provides a small arc discharge inside the arc tube to facilitate subsequent arc formation. Because of the narrow pinch seal area, a formed arc tube lacks the room for the extra electrode. Consequently, a high-voltage ignitor provides the breakdown of the gases to start the arc.
The high voltage pulse generally allows the lamp to start faster from a cold state; but more importantly, the lamp ignites up to 60% faster than a conventional arc tube in a hot restart. Additionally, color uniformity is enhanced, and the loss of lumens over time occurs more slowly, resulting in a 40% improvement in mean lumens.
The new lamp type can be matched with a new 277-V linear reactor (LR) ballast, rather than with a standard constant wattage autotransformer (CWA) ballast system, normally used with a 400-W MH lamp. The 350-W MH lamp/LR ballast combination saves 83 W and the light output is equivalent to that of a 400-W lamp. The MH lamps features an average rated life of 20,000 hours and an apparent color temperature of 4000 K. It is worthwhile studying the range of these lamps.
An often-overlooked specification in an HID system design for a public space is the ballast noise rating. Premium-wound ballasts run cooler and quieter because they are potted or otherwise acoustically dampened. An alternative solution is remote-mounting the ballast-removing it from the fixture in the public space.
Fluorescent strips, hidden in an architectural cove, coffered ceiling, or crown molding, can create bright, cheerful surfaces in a mall setting. The fluorescent source can be a component of, or comprise all the ambient lighting. Introduced in the past two decades, T8 fluorescent lamps use triphosphors that create the appearance of balanced white light. Available with chromacities of 3000K, 3500K and 4100K, these lamps allow warm, neutral, or cool atmospheres to be designed.
The T8 lamp is also available in a U shape with narrow leg spacings-giving designers several options in 2-ft lamps for the increasingly popular 2- by 2-grid ceiling and corresponding fixtures. The fluorescent lamp also comes in T10, T5 and T2 versions. The high-wattage, rapid-start compact, single-ended fluorescent lamps such as GE's Biax , offer high lumen packages in lamps as short as 18 inches. The four-pin, plug-based lamps operate at 18 W and 49 W. These lamps can also be used in 2- by 2-ft fixtures.
Although they're the least efficient source, incandescent lamps offer a variety of beam patterns, tight beam control, and an array of wattages. Used sparingly, they are ideal for highlighting marble, granite, brass, glass, and other finishes.
The tungsten halogen lamp has gained great popularity, and is available in various sizes and shapes. The lamp operates using the halogen, or iodine, cycle. In this process, evaporated tungsten particles return to the filament within the tubular bulb. This keeps the inside wall of the bulb nearly completely free of blackening deposits of tungsten and maintains almost constant light output over the lamp's life.
A family of halogen capsule 50-W PAR 20 lamps has a rated life of 2000 hours. They are available in 120 V and 130 V, with narrow spot and narrow flood beams. These lamps are more compact than standard 75-W R30 lamps, and they offer more precise optical control.
PAR 36 halogen lamps are also available in a low-voltage design with a number of beam spreads. This type is offered in very narrow spot, narrow spot, wide flood, and very wide floods.
Sconces, torcheres, lanterns, and lampposts bring a human scale to interior spaces and can become signature decorative pieces that identify a plaza or court. Even if sparingly used, custom decorative lighting fixtures can create character and a sense of scale while at the same time providing basic building illumination. If desired, they can also be a visible, apparent light source.