Are CFLs Worth Their Price?

Compact Fluorescent Light bulbs (CFLs) are presently being pushed pretty aggressively by energy efficiency organizations, retailers, and even governments. When we go to the hardware store to buy some new light bulbs, though, we find that CFLs often cost 10 times as much as the good old-fashioned incandescent bulbs. In order to see if CFLs are worth their price tag, I compared the total cost of purchase and operation for CFLs and standard incandescent light bulbs over a long period of time. The results show that CFLs will pay for themselves in savings on your electric bill in a matter of months. Keep in mind that the costs shown below are for just one light fixture operated 4 hours per day.

Let’s do a little math. At your local hardware store you can probably find 40, 60, 75, and 100W incandescent bulbs for as little as 25 cents apiece. At the same store, it will likely cost you about $2.50 per comparable CFL. The average life on the incandescent will be about 750 hours, whereas you can expect around 8000 hours out of the CFL. So, when we look at the cost, it only makes sense to do so over a nice long period of time. Otherwise we would neglect the cost of replacing the incandescent several times over the life time of the CFL.

In the graph below I’ve shown the total cost of buying and operating the light bulbs for one light fixture for 8 different scenarios. In this case the light is turned on for 4 hours every day. I intend to delve a little more into this data in a subsequent post, but I hope this plot makes it clear that over a reasonable time horizon (a few months), the CFL will save way more than the purchase cost.

* To get the same amount of light as a 40W incandescent, it only takes 10W for a CFL. For 60W, it takes 13W; for 75W it takes 20W; and for 100W it takes 26W.

To the quality point, there are some CFLs on the market that offer nice, soft lighting. The dimming capability may still need a little work though. The NY Times put together a decent energy efficient bulb comparison table here.

Posted by Luke
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7 comments:

  1. I'm wondering if there are hidden environmental costs to CFL's? Is there anything really toxic or rare that's required to make them? Also, nice graph!
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  2. Good question Ron. As I understand it there is about 5 mg of mercury in a CFL. As a point of comparison old school thermometers had ~500 mg. A more relevant comparison though is the amount of mercury released during the most common form of electricity generation, coal power. Apparently over a 5 year period, an incandescent bulb will use enough energy to release 10 mg of mercury into the air. Over the same period, a comparable CFL will only use enough energy to release around 2.4 mg. So, all told, the CFL (5+2.4= 7.2 mg) represents less cumulative mercury than the incandescent. The small amount of mercury inside the CFL is, of course, only released if the bulb is broken. Please follow these clean-up instruction if you break a CFL: http://www.energystar.gov/ia/partners/promotions/change_light/downloads/Fact_Sheet_Mercury.pdf
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  3. Thanks Ron for the 'toxic' question. This mercury problem has been discussed several times on NPR. Luke's reference to mercury release by incandescent bulbs surprised me. The graph is great, but too large to print. My computer screen is small.
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  4. luke, thanks for simplifying thingsfor 55 yr old,prematurely senile people.im off to the hardware store
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  5. Ok, so I have replaced all the most frequently used light bulbs in my house with CFL'S, for free courtesy of my electric provider. I have not really noticed any savings on my electric bill, at least nothing to get excited over.
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  6. In your opinion how do CFLs compare to LEDs - light "temperature" and environmentally?
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  7. MEEH,
    When we wrote this post, LED's were still crazy expensive and there were very few that could be dropped in to existing fixtures. That has changed and is continuing to change in a great way.
    We haven't yet done the lab testing at PlotWatt to assess performance (temperature, dimming, etc.) and I suspect the life cycle cost analysis (given fairly serious raw materials input) makes their environmental footprint pretty serious. But their lack of mercury, awesome efficiency, and long life ought to make up for that over time.
    I'm reminded of the Miles Per Gallon / Gallons Per Miles conversation. The energy benefit of going from energy wasting incandescent bulbs to CFLs is big. Thats like trading your pickup for a compact car. Incandescent to LED is slightly bigger. That's like pickup to hybrid. Beautiful! But CFL to LED might be misdirected (if energy saving is the goal) b/c that's like trading your compact car for a hybrid. Yes, there will be energy savings but it may take years (or even decades) to realize a payback. I know that wasn't your question... sorry for the tangent.
    To answer your question, we have some testing to do! Thanks.
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