More energy efficient: In well-used room, keeps lights on or turn off/on?

LaurelC — Tue, 06 Oct 2009 17:51:42 GMT

My husband and I have a friendly wager re: whether to turn lights off or leave them on when using a room off and on throughout the evening. We use both compact flouorescent light bulbs (CFL) and incandescent bulbs in our home. Would you tell us who wins the bet?

RE: More energy efficient: In well-used room, keeps lights on or turn off/on?

citrine1 — Tue, 06 Oct 2009 18:37:40 GMT

If you are going to be out of the room more than 15 minutes, turn the lights out. If less than 15 minutes, leaving them on is okay as it will burn about the same amount of electricity to turn them on again after having turned them off. Who cares who wins? Just kiss in the dark, then turn the lights on and do it again. Did it feel any different with the lights on or off? :)

RE: More energy efficient: In well-used room, keeps lights on or turn off/on?

Lido — Tue, 06 Oct 2009 20:30:48 GMT

Good answer, citrine1.

RE: More energy efficient: In well-used room, keeps lights on or turn off/on?

EnergyFred — Tue, 27 Oct 2009 23:10:04 GMT

The typical maximum power that can be pulled from your socket is 1800 watts during turnon of a grid connected device. If your CFL is 20 Watts continuous then for energy consumption your breakeven time would be 1/90 of the turn on time or < 2 minutes.

A more serious problem is how much off / on /off / on cycles impact the lifetime of your CFL. I would guess that 10 - 15 minutes of off time would be a winner overall.

If you really want to settle further energy questions, get an inexpensive watt/energy meter such as the Kill-A-Watt available for $26 + shipping from

http://store.solar-electric.com/kiacpomome.html

You can also download the manual from this site.

An incandescent bulb has a cold resistance of about 10% of its operating resistance so it pulls about 10 x its rated power during warm up.

Note that the turn on transient put much higher stress on the filament than just operating. (Don't most incandescent bulbs burn out during turn-on?)

regards, EnergyFred

RE: More energy efficient: In well-used room, keeps lights on or turn off/on?

LaurelC — Wed, 28 Oct 2009 14:31:26 GMT

For some reason I didn't get an email notifiying me of citrine1's answer, and no, it didn't feel any different :-D

EnergyFred, you are speaking a bit above my head. I do understand what you are saying re: the on/off cycle decreases the life of CFL bulbs. Are you further saying that if you are going to leave the CFL off for at least 10-15 minutes, then turn it off? And you are absolutely right (though I suspect you knew that) about incandescent bulbs burning out right at turn on! So in the end, what do you do in Your house, with both incandescent and CFL bulbs (and if you don't have both, just pretend!) Thanks to all!