I was part of a discussion over email this week about whether we should recommend faculty turn off lights when they leave a classroom. A professor suggested all faculty members at Lasell College get in the habit of always turning off lights. A second professor responded that it was his understanding that it takes more energy to turn lights on and off than if they were left on all day. Naturally they turn to the young environmental science professor to settle this debate.
I'm not an engineer so I really don't have much experience with ballasts and inrush current. It was an interesting question so I took some time to do a little research. I too have heard the claim that turning lights on and off uses more energy. It turns out that turning lights on does require a surge of energy but the quantity is about the same as the amount of electricity used to run the lights 2 to 5 seconds. In other words, if the lights will be off for more than five seconds there will be an electricity saving.
If electricity is your only concern turning lights on and off is the way to go. Unfortunately bulbs take on more wear when they are turned on and off and will require more frequent replacement. I ran into a range of recommendations but many suggested the best approach is to turn the lights off if it will be longer than five minutes.
I'm not going to promote that here at Lasell College though. I think our best approach will be to create a culture of everyone turning off the lights when they can. It may mean replacing a few more bulbs but I think if there is any fuzziness people will not do it. The message needs to be clear, "Turn off the lights when leaving the room." A message saying, "Turn off the lights if you think they will be off for more than five minutes" is destined to fail.