Rapid Start (RS)
Rapid start ballast applies 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 the instant start. They will typically not be able to start lamps reliably under 50 degrees F.
Instant Start (IS)
Electronic instant start ballast applies a high voltage across the lamp with no preheating of the cathode. THIS IS THE MOST ENERGY-EFFICIENT starting method for fluorescent lamp ballasting. An instant start ballast use 1.5 to 2 watts less per lamp than a rapid start ballast. Other instant start 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 a 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.
For information on when a LED works with a fluorescent ballast see our LED wiring options page.