Published In September 2001
Pulse-start metal halide ballast and lamp systems bring a wealth of benefits to users of high-intensity discharge (HID) lighting. Prior to the development of pulse-start systems, metal halide lighting delivered white light at the cost of operational inefficiencies. For this reason, lamp manufacturers sought to improve probe-start metal halide lighting by changing its chemistry and increasing the fill pressure in the lamp arc tube to increase lumen efficiency. Pulse-start ballast/lamp systems are an especially useful replacement for high-pressure sodium (HPS) systems in applications that have high bay ceilings and require high-quality light in terms of color rendering. Applications include gymnasiums, recreational facilities, warehouses, ‘big box’ retail outlets, assembly facilities, supermarkets, and roadways. Pulse-start metal halide lighting systems can provide efficiencies that approach those of HPS systems—superior light output, high lumen maintenance and long life—but without HPS systems’ hazy yellow illumination. In addition, pulse-start lamp/ballast systems have the following advantages over conventional metal halide systems: n More lumens per watt—lumen output increases by 25 to 50 percent, depending on lamp wattage and burning cycle. • Improved lumen maintenance • Longer lamp life—up to 50 percent • Reduced color shift—two-thirds reduction in color temperature change over life • Improved lamp-to-lamp color consistency—color consistency to ballast regulation capabilities • Faster warm-up • Quicker restrike—restart time for hot lamps after a momentary outage reduction from 15 to 20 minutes to three minutes • Color characteristics—a Color Rendering Index (CRI) of up to 85, representing a 30 percent improvement Separation optimizes performance The first step towards the development of significantly improved metal halide lamps was the introduction of a high-voltage igniter as a component to the ballast. The igniter delivers a high-voltage pulse directly across the lamp’s operating electrodes to start the lamp, replacing the ballast’s 600v peak voltage and eliminating the lamp’s internal starting probe and its protective switch. Incorporating an igniter in the design of the pulse-start ballasts overcame the major barrier to re-engineering probe-start lamps. Lamp manufacturers could now use new arc tube designs and materials, which allowed for higher operating pressures and new chemical fills. Replacing the internal starting probe with an igniter allowed a separation of ballast starting and operating functions. The igniter starts the lamp and the ballast’s core and coil operates the lamp, allowing for optimization of lamp and ballast performance. Cooler operation for longer life The traditional lead-peak metal halide ballast, with its 600V peak open-circuit voltage needed to start probe-start metal halide lamps, creates a high lamp current crest factor that compromises lamp performance. Isolating lamp starting and operating functions makes ballast operation more efficient and cooler because the ballast’s core and coil no longer need to supply the 600V starting voltage of probe-start metal halide ballasts. The ballast’s open-circuit voltage requirement is now reduced to the operating requirements of the lamp. This lower open-circuit voltage creates lower ballast operating temperatures, resulting in longer ballast life, reduced maintenance/replacement costs, and the possibility of higher fixture ambient temperature ratings. The future of HID lighting Lighting researchers are finding that the blue-rich light of metal halides and fluorescent lamps provides better “seeability” under the low illumination levels of parking lot and roadway lighting. Industry-wide, metal halide lamp sales are growing by 12 percent per year, while HPS sales are only growing by about 4 percent. Pulse-start metal halide is clearly the future of HID lighting. Consider the performance characteristics of HPS lamps versus traditional probe-start metal halide lamps. HPS outperforms probe-start metal halide in all quantifiable categories—particularly light output and life—except color. Metal halide light is a desirable white color compared to the yellow color of HPS. However, HPS’s greater light output, lumen maintenance, lamp efficacy (lumens per watt), when compared to probe-start metal halide, have resulted in its widespread application since its inception in the 1960s. With the invention of the pulse-start metal halide system, and its subsequent performance improvements over the previous probe-start technology, the advantages of HPS over metal halide are virtually erased. CUMMINGS, senior product manager, HID Ballasts at Advance Transformer Company, a manufacturer of electronic, magnetic, HID, and electronic HID ballasts. He can be reached at email@example.com or (847) 390-5112.