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Ask Mr. Tight-Watt: Turning off CFL Lights  Smart Choices Archive

Ask Mr. Tight-Watt: Turning off CFL Lights

Should you turn the lights off when you leave a room?

Ask Mr. Tight-Watt

Q: Should I turn off my “curly” CFL lights when I leave the room for a short time?
—A Smart Choices Reader

Answer from Mr. Tight Watt: According to the Lighting Design Lab, Energy Efficiency and Renewable Energy and Scientific American, the “magic number” is about 15 minutes. In other words, if you’ll be back in the room in about 15 minutes, leave it on. If you’ll be gone longer, turn it off.

The science is that there is a trade-off point between the money/energy spent turning the light on and off and the cost of wearing out the lamp with frequent starts.

Myths about CFLs, from Lighting Design Lab
1. It takes more power to start up a CFL than to leave it on.

Truth: The spike to start a CFL lasts only about 1/10 of a second and draws the equivalent of about 5 seconds of operation. In actuality, leaving the lights on for longer periods uses more energy than turning them on and off, when you leave them on for longer than 15 minutes.

2. Turning CFLs on and off wears them out quickly.
Truth: Fluorescent lights are rated to last about 20,000 hours when left on for 3 hours, or about 6,667 starts. Every time you start a bulb, a tiny bit of coating is burned off. If you have more starts, you will burn the coating off a little faster, but you won’t see a noticeable difference. 

See the following for more details:


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