Lights Use More Energy While Turning On

July 30, 2010 at 5:00 am Chad Upton 1 comment

By Chad Upton | Editor

There is a belief that it takes more energy to turn a light bulb on than it does to leave it running. That is true.

But, in some cases it’s still more energy efficient to turn the lights off when you leave the room.

That’s because the spike of additional electricity that is used to turn on a light bulb, is very short lived. That extra energy varies depending on the type of light bulb.

For most bulb types, the extra energy is equivalent to less than one second of energy that is consumed while the light is on. That means, you’d have to leave the room and return within one second to save energy by leaving the light turned on.

The one exception is fluorescent tubes (not compact fluorescents), they require a lot more energy to turn on than they consume while running normally.

Depending on the source of the information, fluorescents use energy equivalent to 5 to 24 seconds of regular use, just to power up. Therefore, if you use fluorescent tubes, there would be times when it would be more efficient to leave them on than turn them off.

If you have a large room that is lit with fluorescent tubes and you were going to leave the room for a few minutes or less, it would be more efficient to leave them on instead of turning them off and then back on when you return. But, if you’re leaving for more than that, you should shut them off.

That said, turning lights on and off does cause wear and tear on the bulbs. LED “bulbs”, which are now available at most hardware stores, are most resilient to this type of wear and tear.

Incandescent bulbs are extremely cheap, so the cost of replacing these bulbs isn’t an important consideration, although the environmental impact may be. But, it is important to consider this wear and tear for more expensive bulbs such as compact fluorescents. It is for this reason that the EPA recommends that compact fluorescent lights are used in areas where they will usually be turned on for at least 15 minutes at a time. This will contribute to bulb lifespan.

Although I used a couple other sources for this post, Mythbusters did some great experiments on this subject and I’ve embedded the video if you’d like to watch it.