When should I replace my lightbulbs?

February 8, 2006 7:16 AM

At what point in the lifespan of a conventional incandescent lightbulb is it most cost-effective to replace it with an energy-efficient bulb?

Will I save more money by throwing away a perfectly good bulb and replacing it with a more efficient one, or should I wait until the old bulb burns out completely? Is there some magic point in the middle at which I should replace the bulb to maximize my savings? There are too many variables to wrap my Bachelor of English head around the math.

And for the true million dollar question, I moved into a new house four months ago. Whenever a conventional bulb (left by the previous owner) burns out, I replace it with an efficient one. There are several bulbs that have yet to die. Without knowing exactly when they were installed or how much life they have left, is there any formula that would tell me whether or not I should replace them now?

posted by Faint of Butt to home & garden (17 comments total)

just switch them now. The old bulbs have zero cost to you...they came with the house. Replace with energy efficient ones NOW to start realizing some savings on power bills.
I switched all our incandesetns to compact flourescents about a year ago, and saw a SUBSTANTIAL drop in the power bill.
posted by cosmicbandito at 7:31 AM on February 8, 2006

Not knowing how old the bulbs are throws an unknowable variable into the mix, so there is no way to compensate for it. Here is a department of energy comparison between CF and regular bulbs, which you can use to gauge costs, EXCEPT notice that their initial starting cost for compact flourescent is ridiculous (over $20). Move the blue bar down for real results.

From the look of it, unless you assume that your old bulbs will burn out within 3 months anyway, replace them. Truly, the savings realized by looking for the 'magic point' where incandescents are worth using is pennies, and you can console yourself by keeping in mind the added benefit of reducing pollution.

That's true as long as you have appropriate facilities for recycling CF bulbs available when they do burn out, however. Many contain mercury and you shouldn't just throw them away, but if you have an IKEA anywhere near you you can dispose of your CF bulbs there. We've been using the new bulbs for over two years, however, and have yet to replace one. Our power savings were considerable, too.
posted by Dipsomaniac at 7:33 AM on February 8, 2006 [1 favorite]

The biggest factor is how often you use the lights. If you seldom use them then the energy difference in replacing them is negligable. If you use them alot and they are high wattage bulbs then replace them. A closet incandescent bulb should probably be left alone unless you keep it on constantly to ward off the closet monster.
posted by JJ86 at 8:07 AM on February 8, 2006

I've been replacing incandescents with compact flourescents as they burn out, but I'm seeing really really short lifespans on the compact flourescents. We've been in the house two years, and I've got a box of about six burned-out compact flourescents.

I've got some track lighting on the ceiling in the kitchen, two stories up. I get vertigo going up that high on the ladder in the middle of a room, so I want to go up there as little as possible. I've replaced almost all of those floods [R-45?] with compact flourescents, thinking that'll reduce my trips up on the ladder to once every 6 years. I noticed last night that one of my < 2-yr-old compact flourescents is out up there.br>
These are Fein brand, bought on sale at Menard's. Are they crap, or is this not unusual?
posted by chazlarson at 8:38 AM on February 8, 2006

IMO discarding a light bulb that hasn't burned out is throwing away money -- the replacement bulb's type isn't a factor, yet.
posted by Rash at 8:54 AM on February 8, 2006

Chazlarson, you might try a different brand. I have compact fluorescents in daily use that are positively antiques. That said, if your bulbs are used heavily, like 7 or more hours a day, in 2 years you hit 5,000 hours, where statistically a few out of a hundred 10,000-hour rated bulbs could blow, just as an incandescent can blow after 500 hours rather than the typical 1000. IMHO it is worth investing in the best quality ones, which are typically the longest-rated at 15,000 hours, even if it costs a little more. Philips, GE, Sylvania is what I have. When one or two of your track lights burn out, go up and replace all of them at once, to minimize ladder trips. Then use the partially-used bulbs in more accessible places.
posted by beagle at 8:55 AM on February 8, 2006

chazlarson writes "I'm seeing really really short lifespans on the compact flourescents. "

There is a lot of of difference quality wise between different brands. Both in spectrum, warm up time and lifetime. Try going with a more expensive bulb by a company you've actually heard of. I've had no problem with our GE and Sylvania bulbs but the no-names we got at the discount store were horrible.
posted by Mitheral at 9:02 AM on February 8, 2006

On the original question, let's say the average bulb in your house is 60 watts and has 500 hours of life left, and your electricity costs $.15/KWH. You'll use 45 cents worth of juice until it burns out. Then you'll spend, let's say, $7 on a 13 watt CP, which puts out equivalent light, after which the same 500 hours of use will cost you only 9.7 cents. So replacing now rather than later will save you 45-9.7=35.3 cents. You'll spend the $7, or whatever it costs, on the CP sooner or later anyhow, so that's irrelevant (unless you were to put it in a savings account and earn 1.5% interest on it, or 10.5 cents in a year.) The Wiki page has a life-cycle cost comparison betwen fluo and incan.
posted by beagle at 9:02 AM on February 8, 2006

Compact flourescents are sensitive to heat. I had some in an enclosed fixture that died prematurely due to excess heat buildup. Granted, there's a lot LESS heat being generated by the bulbs, but if you keep 2 100W equivalent CF bulbs in an enclosed fixture, the heat will shorten their lifespan. These 2 had visible browning of the plastic on the bases. Also, like the other posters said, buy a decent brand.
posted by cosmicbandito at 9:10 AM on February 8, 2006

chazlarson: no, you're not alone; in my experience compact fluorescent bulbs have not appeared to last any longer than incandescent bulbs. I have a couple that haven't burned out yet but the experiment was definitely a disappointment.
posted by Mars Saxman at 9:19 AM on February 8, 2006

Good answers, folks! I think I'll replace the bulbs as soon as I get around to it, rather than waiting for them to burn out. And I can recycle the compact fluorescent bulbs at Ikea, you say? A perfect excuse to eat meatballs!
posted by Faint of Butt at 9:22 AM on February 8, 2006

A while back I was at Fred Meyer and there were coupons for $2 off CFL bulbs attached to all the packages there. (The coupons were from the local utility company.) A package of three CFL bulbs was like ten bucks... then you got six off with three coupons. It was a deal, and the bulbs were fine too. Still using them two years later...
posted by kindall at 9:33 AM on February 8, 2006

As Mitheral said, there is a vast range between CF bulbs, watch for colour, turn-on time (from flipping switch until constant light), warm-up time (from flipping switch until full brightness), and reliability (doh!). I've also had the overheating problem cosmicbandito had. It was pretty surprising, they lasted for about a year, but the heat damage was obvious (these where luminus bulbs from costco).

I would look online for recommendations rather than trusting brand names. unfortunately, lifetime is the hardest property to evaluate. You might be able to find industrial bulbs rated for extremely long life, but I think those applications are using LED bulbs now, which are way more expensive again, and who knows if the colour is nice...

Here are a couple of older threads on compact fluorescent: Pick me a light bulb, Will I burn down my apartment.

Finally, my opinion of the CF bulbs I've tried is here. I can also add another type to the list:

13W NOMA bulbs from Canadian Tire. .5-1s turn-on delay, very close to full brightness right away. Brightness was very good but the colour is a little blue/white (especially compared to the luminus bulbs from costco). The same plastic base as luminus and other models, but the spiral is slightly shorter and slightly smaller diameter.

Finally, you shouldn't be paying anything like $7 a piece for regular use CF bulbs! 13W bulbs are widely available for $1-2 CAD.
posted by Chuckles at 9:58 AM on February 8, 2006

Regarding surprisingly short lifespans, you could also have a bad fixture or a bad electric line contributing. I had a CF burn out quickly; after two more incandescents in the same fixture burned out quickly, I replaced the fixture (after an electrician verified it was the fixture and not the line) and haven't had any problems since.
posted by Zed_Lopez at 10:45 AM on February 8, 2006

Many CFLs will guarantee a certain lifespan - anywhere from one to seven years. So if you've been having problems, you should definitely check out a guaranteed brand. There are often programs from your local utility to encourage the purchase of them - generally coupons or rebates will be available.

One note: Many CFLs are Energy Star rated, but not all. Be sure to check for the Energy Star label to make sure you're getting the most efficient product possible.
posted by Jart at 11:28 AM on February 8, 2006

Many contain mercury and you shouldn't just throw them away

I recently read that the amount of mercury in them is so little as to be moot: a coal BBQ is going to release more mercury in one cooking session than the bulb. Or something like that.
posted by five fresh fish at 12:42 PM on February 8, 2006

Yes, there are el cheapo CF bulbs, but I'd still go for a $7 or so GE or Philips model. In my 10-year experience using these, they will last the rated 10,000 hours, in the course of they save you about a dozen incandescent replacements and around $70 worth of electricity. It is worth checking with your electric company, they often have good brand name bulbs available at essentially wholesale cost to their customers.
posted by beagle at 12:53 PM on February 8, 2006