This specialized lighting flipper enables one ballast to alternately operate two lamps. In this case up to 10 ballasts and 20 lamps. The idea is when the photoperiod is over in one location the lamp power is switched to a lamp in another location. For instance 12 hours in room A and 12 hours in room B. The advantage is you only need half as many ballasts as you would otherwise. This is particularly useful when running ballasts with an off-grid power generator.