Weird & Wireless: CFL, LED, and the incandescent bulb

Welcome again to the wonderful but sometimes weird world of wireless comms, written by Joel Young, CTO of Digi International.
I keep hearing about CFL and LED. What’s the difference between these types of light technology and the classic incandescent bulb? Which is the best?

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?


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.

(Picture - The incandescent light bulb by Anton Fomkin, under Creative Commons attribution licence)

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joel-young-2009-150x150.jpgJoel Young, VP of Research and Development and CTO at Digi International, has more than 22 years of experience in developing and managing data and voice communications. He joined Digi International in June 2000 and in his current role he is responsible for research and development of all of Digi's core products.

Prior to joining Digi, Joel was VP of Sales & Marketing at Transcrypt International where he was responsible for sales, marketing, and product development for all information security products. During his tenure at Transcrypt, he also served as VP of Product Development and VP of Engineering where he was responsible for engineering, research and product development for wireless communications products, cellular telephony, wireline telephony and land mobile radio, data security and specialized digital radio products.

He also served as District Manager for AT&T Business Communications Services where he was responsible for the creation and implementation of voice processing and network database strategies, including deploying new voice processing platforms into the AT&T switched network for private network and other outbound calling services.

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