Don't Turn Off CFLs If You're Leaving a Room for 5 Minutes

If you're one of the "every little bit counts"-types of green dwellers, you've probably gotten into the habit of shutting off your lights when you leave a room. But in the back of your head, you're reminded of that old wives' tale: It takes more energy to power up the lights again than you're saving by shutting them off. Those old wives are sometimes right, though. Depending on how long you're stepping out, it might save watts to keep the lights on, and the magic number depends on the type of bulb.

Of course, if you're leaving the house for an 8-hour workday, you should definitely be turning off unnecessary lights—for both mother nature's sake and for the sake of your wallet.

But if you want to know if it's a good idea to shut off your CFL bulb when you leave the room for just a few minutes, it gets trickier. Luckily, Reader's Digest's green guide spelled it out for us:

INCANDESCENT BULBS: Shut these power suckers off if you're leaving a room for anything more than 5 seconds.
CFL BULBS: Shut them off if you're leaving a room for more than 15 minutes.

So if your living room light fixture is stocked with CFLs, it's not worthwhile to flip the lights off for your short bathroom break. But if you're rocking incandescent bulbs, or have been eating plenty of fiber, you might want to hit the switch.

via Reader's Digest

(Images: Flickr member jspad licensed for use under Creative Commons, Flickr member danmachold licensed for use under Creative Commons)

Comments (10)

This is a great tip. I've been wondering where that magic line is. It appears I've been turning mine off too often. I wonder if there is also a point at which you'd actually be more efficient with an incandescent. For example, I have a light in my kitchen that rarely gets turned on more than five minutes.

Mythbusters did this a couple years ago, and they say that even with CFLs, it's less than 1 second. Looks like Reader's Digest is BUSTED! :)

http://kwc.org/mythbusters/2006/12/episode_69_22000_foot_fall_lig.html

That doesn't make sense. This implies that the amount of energy used by an incandescent bulb in 5 seconds is equal to that used by a CFL in 15 minutes. Not even LEDs increase efficiency that much.

Yeah...I think I'll trust Mythbusters on this one, since they describe their methodology, whereas Reader's Digest gives no indication of where their numbers are coming from. For all we know, they grabbed them from someone else who was citing old wive's tales.

Turning bulbs off and on subjects them to wear, and it takes quite a bit of energy to make a new bulb.

I generally take my chances and just never turn on my bathroom light. There's a window there, so even at night it gets some light.

For those that say turning on and off lights kills them faster, you are right. But in my environmental control systems class (for architecture degree) we looked at all the major lamp (bulb) types and looked at cost analysis over time. It costs way more to just keep them on than it does to turn them on and off even a hundred times a day. Remember, turning them on and off may decrease their life span, but keeping them on is using up that life span as well.

As for the tip given in this post, it's also untrue. Mythbusters explained their logic and methodology. The whole "warm up" time refers to an amount of time when you first turn on a lamp in which it is drawing more power than its normal warmed up state. Mythbusters also got this one right. Even with a CFL, the warm up time is long (sometimes 20s or more), but it doesn't draw that much more power than its normal state. Also, if you are leaving the room for a minute, the bulb isn't going to completely cool down in that time. It's better to just turn it off.

CFL's aren't worth the added energy savings. They contain mercury and the manufacturing websites contain specific disposal guidelines that they don't include on the packaging. I think this technology is not worth the savings if the discarded bulbs are allowing mercury into the soil.