If the device is reasonably well designed, turning it on and off in normal use shouldn't shorten it's life much. That means normal use, not turning it on and off every 30 minutes.
Fluorescent lamps, however, take time to go to full brightness, and their life shortens if they're turned on and off frequently. Probably isn't a good idea to turn them off, if you know you're returning to the room in less than, say, 1 hour.
Fluorescent lamps, however, take time to go to full brightness, and their life shortens if they're turned on and off frequently. Probably isn't a good idea to turn them off, if you know you're returning to the room in less than, say, 1 hour.
