I'm assuming those are T12 fluorescents. If so, you generally don't have to worry about the switch causing burning. If the light is significantly brighter, you may notice some reddish color developing int the leaves. This depends on the plant, and I generally don't worry about it. With T12 you need to have the bulbs fairly close to the plants-12 inches or less. Lights, not matter the type should be left on 12-16 hours a day as a general rule.