Most of us were taught to turn off the lights when leaving a room, but if you have fluorescent bulbs, think again. It takes a lot of energy for them to turn back on. In fact, it's most efficient to only off fluorescent lights if you’re leaving a room for more than 15 minutes. Incandescent lights, on the other hand, should be turned off whenever not in use—doing so saves energy. It also keeps the room cooler, since only 10% of the energy fluorescent bulbs uses actually results in light; the rest is turned into heat.