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Ballasts are designed to provide the proper starting and operating voltage required for the lamp.
In all fluorescent lighting systems, the ballast performs three basic tasks:
- Provides the proper voltage to establish an arc between the electrodes.
- Regulates the electric current flowing through the lamp to stabilize light output.
- Supplies the correct operating voltage to provide the specified lamp operating current. Ballast map also compensate for supply voltage variations.
In rapid-start fluorescent systems, the ballast performs an additional function, providing continuous voltage to maintain heat in the lamp electrodes—at a level recommended by the lamp manufacturer during lamp operation. If electrode filaments of a rapid-start lamp are not continuously heated, they may deteriorate prematurely, shortening lamp life.
Rapid Start (RS)
Rapid start ballast apply a low filament voltage to preheat the cathodes. Simultaneously, a starting voltage (lower than that used in instant start) is also applied to strike the arc. When the cathodes are hot enough, the lamp will strike. The filament voltage continues to be applied throughout the operation of the lamp. Rapid start ballasts appear to have a slight turn on delay compared to instant start. They will typically not be able to start lamps reliably under 50 degrees F.
Instant Start (IS)
Instant start ballast apply high voltage across the lamp with no preheating of the cathode. THIS IS THE MOST ENERGY EFFICIENT starting method for fluorescent lamp ballasting. I.S. ballast use 1.5 to 2 watts less per lamp than rapid start ballast. Other I.S. ballast benefits typically include parallel lamp circuitry, (ballast wired with parallel lamp circuitry is what allows other lamps to continue burning when one or two go out without damage to the ballast or lamp), longer remote wiring distance, easier installation due to less complicated wiring, and capability to start lamps at 0 degrees F versus 50 degrees for rapid start.
Glow to Arc Transition
In order to achieve full rated lamp life, a ballast should start a lamp so that the time from when the lamp begins to glow to the time the lamp arc strikes should be as short as possible.
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