When should I turn off standard fluorescent fixtures?

It is a myth that it costs more to turn off fluorescent lights than to leave them on. This was true in the 1940s when fluorescent lamps first became popular because turning them off and on again greatly shortened the lamp life. Today’s lamps are not as affected by start-up damage and the energy surge to start them up is so small that it’s cheaper to switch them off when they’re not needed.