An instant start ballast does not preheat the electrodes, instead using a relatively high voltage (~600 V) to initiate the discharge arc. It is the most energy efficient type, but yields the fewest lamp-start cycles, as material is blasted from the surface of the cold electrodes each time the lamp is turned on.

What's the difference between a rapid start ballast and an instant start ballast?

Instant start lamps don’t use a preheating method. Instead, they send a high amount of voltage across the lamp upon the strike. Typically, instant start ballasts use 1.5-2 watts less per lamp than rapid start ballasts. Instant start lamps also start reliably at temperatures as low as zero degrees.

What is an instant on ballast?

Instant start ballasts are ideal for use with fluorescent lamps that are not switched on and off frequently. Such a type of ballast provides a high amount of voltage to the lamp when it is switched on, but without pre-heating the cathodes either during the start or while the lamp is lighted.