Of course, in today’s world, we are all being encouraged to discard those ancient incandescent bulbs for the new compact fluorescent lamps (CFL) and light emitting diodes (LED), which for most of us seem really expensive to buy. I admit that I never really liked the traditional tube fluorescent lights, probably because first, I always have trouble getting the bulbs in - it seems that I always have them out of alignment and second, I usually buy cheap lights that have ballasts that go bad. But I must admit, now that I’ve started using the screw in CFLs (like the one pictured), I’ve had quite a change of heart. I’ve yet to take the plunge into the world of LEDs however, primarily because I haven’t yet been able to justify the expense. And for me, they always seem to look blue. Nonetheless, I know that someday I will make the switch as they all will become clear with the obligatory advancement of technology.Recently I set out to compare our friends, the CFL and the classic incandescent. The following two tables illustrate the characteristics for a range of incandescent bulbs from 25 watts to 200 watts and a range of CFLs from 5 to 40 watts. Assuming you turned on each light and left it on for a full year, how much would it cost, including bulb replacement and electricity?
Incandescent (5,000 hour life)
CFL (10,000 hour life)
As you can see, the lumens per watt increases as wattage increases for both types of bulbs. In addition, notice that the lumens per watt or luminous efficacy value is 6 to 8 times greater for CFLs than their incandescent brethren and they last twice as long. As such, even though a CFL costs 5 to 6 times more than an incandescent bulb in the store, the loaded cost per year of a CFL is still about 20% of an equivalent incandescent.
Of course that looks good on paper (or on a screen), but what does it mean in real life? In 2008 my house had about 90 incandescent lights totaling 6750 watts. At a 6% duty cycle, I used a total of 3,544 kWh on lights at a cost of about $373 (don’t ask me how I know this - just accept the fact that we engineers like data). Anyway, these 6,750 watts put out about 61,875 lumens. Using the equivalent light in CFLs, I figure I would need only about 955 watts of CFLs to get the same light. At the same duty cycle this would be only 501 kWh at a cost of $53 - an annual savings of $320. Note that replacing all 90 bulbs at $3 each would cost only $270. I think I had better get started.
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