S. is correct. There's more energy consumed getting a light to light than keeping it lit. So flicking it on an off is a little wasteful. Its not a big deal. Otherwise, people wouldn't use Christmas light that blink all the time.
Somewhere on the outside of your home, is a power meter. It counts EVERY watt you use. But it only goes up by 1 for ever 1000watt/hours you use. So it would be very hard to see the power wasted by flicking the light on and off a couple of times. But if fact it is a little wasteful.