Another common argument against them is that if the CFLs happen not to last their advertised time, 6000 hours to 10,000 hours, then that additional expense has more than wiped out the gain.

Well, good news. CFLs have come down in price to the point where even if they fail well before their expected time, they are still cheaper to operate. Let’s run the numbers. 

Walmart.com recently had a national brand of 15 watt CFLs listed, in a 6-pack bubblepack for $19.32. This is about $3.32 per bulb. I have not priced incandescents recently, but let’s be generous and say you can find a 4-pack of the equivalent 65W bulb for about $1.oo, or $0.25 per bulb. (The 65W equivalency figure is from walmart.com’s description of the CFL.)

For illustration, lets use a figure of $0.10 per kilowatt-hour (KWH) for the cost of electricity, a typical rate. 

Let’s assume that the incandescent lasts its rated time 800 hours. If the incandescent lasts 800 hours, it will consume 65 watts for each of those hours, for a total of 52,000 watt-hours, or 52 KWH. That is $5.20 of electricity, on a $0.25 bulb, for a total cost of ownership of $5.45.

Compare the CFL. Let’s assume, just for illustration, that the CFL only lasts as long as the incandescent, 800 hours, and then promptly fails. Remember, the typical CFL is rated for at least 7 times that, but we’ll handicap it to prove the point. If the CFL lasts 800 hours, it will consume 15 W for each of those hours, for a total of 18,000 watt-hours, or 18 KWH. That is $1.80 of electricity, on a $3.32 bulb, for a total cost of ownership of $5.12.

Even if the “expensive” CFL and the “cheap” incandescent last the exact amount of time, the CFL is still cheaper!

This was not always the case. Back in the mid-1990s, when I first started buying CFLs, they were hard to find and cost $13 to $20 each. They saved energy and money, but it took longer to make back the investment. With prices as low as they are now, you absolutely cannot go wrong with a CFL–even if they only last as long as an incandescent. 

Remember, we were handicapping that CFL lifespan to prove our point. On average, CFLs last the advertised thousands of hours, meaning you can save so much money on  these things you should weep for joy every time you use one. They are THAT good…and THAT cheap. 

Note. A CFL contains mercury (about 5 mg or so), so a CFL that fails early is not a good idea because that increases the amount of mercury in the waste disposal system. You want your CFLs to last a good long time for that reason, too, in addition to saving you buckets of cash.