May 1, 2011
Readers are still fascinated by CFLs. They have some suggestions as to why they fail, who's making them, and how they might give electric companies fits when it comes to billing.

CFLs still a hot topic

Readers are still fascinated by CFLs. They have some suggestions as to why they fail, who's making them, and how they might give electric companies fits when it comes to billing.

Why CFLs fail

I read the letters regarding CFLs in your March issue with interest, being manager of R&D for an LED manufacturer. I believe the assumption that it is better to leave a CFL on for at least 15 minutes to get a longer life is false. However, it is true that the more a CFL is turned on and off, the earlier it will fail.

How many times have you seen a lamp fail after it has been on a while compared to instances of failing when the lamp is first turned on? In my limited experience, lamps fail at least ten times more often when first powered on. Just a note: The turn-on transient power to a 100-W incandescent lamp may approach 1 kW for a short time. Thus a lamp designed to work at 100 W must be able to swallow 1 kW.

Highly accelerated stress testing (HAST) has long be used as it cycles power on and off and cycles ambient temperatures to both hot and cold. HAST is used to quickly separate out failures and identify both manufacturing and design weaknesses by greatly accelerating failure rates.

High temperatures also accelerate failure rates. If a lamp is operated at 100°F rather than 68°F, the failure rate is almost four times higher, that is, it fails in one quarter the time. Too bad most lamp fixtures do not allow sufficient cooling of the lamp.

Also, CFLs must use low-cost components in the power supplies (ballast) to be cost competitive. They must also be small enough to fit in a compact package, which also shortens their life.

Again, it isn't the short ‘on’ time which shortens life, but the frequent turn on cycles and cost/design constraints.
Bruce C. Johnson

I had to laugh at the letter from an anonymous reader (March/April issue). Sounds like he would like CFL and LED-type bulbs to do everything for him and then some. More cost effective, burn cooler, last longer, put out more light, come in a variety of color temperatures, be non-polluting. Why not add auto dimming and disco ball mode?

He doesn't seem to understand that you don't get something for nothing and until a technology is more widely adopted, it will be more expensive and contain fewer features than the mass produced standard that everyone actually uses.

And concerning the American-brand LED bulbs he bought from Wal-Mart: a little investigation will show that despite the name, most if not all products marketed under this brand name are not made in the U.S. (Just another one of Wal-Mart's tactics.) It does not matter what the technology is, you get what you pay for.

Buy a cheap LED bulb made in some poor country and you get a poorly made product. Spend a few bucks for a quality LED bulb and you will get a bulb that will far outlast incandescent bulbs. And yes, they are available in different color temperatures and luminosities that are approaching those of the brightest incandescent bulbs.
Doug Curtis

I just read your letters section and was surprised not to see more discussion about the engineering aspects of CFLs. Measurements have been made that demonstrate a power factor of approximately 0.5 for CFLs. By the way, incandescent bulbs have a power factor close to 1. Right now, consumers get a break because they pay for watts. The electric company gets stuck having to provide energy in the form of volt-amperes. With a power factor of 0.5, however, the electrical supplier must generate twice as much energy as what they are billing for. It would seem to me that power utilities would not be happy if there were a wholesale conversion to CFL lighting. Perhaps smart metering is their way of charging for all energy used instead of just watts. But if they were to bill for all power consumed, then CFLs would not appear to be great energy savers after all.
Richard Thibedeau

When wind power makes sense

As soon as the project that I am involved with can make wind turbines that produce a true and satisfactory ROI without any government subsidies, I will let you know. However, all of those would be in the 10 to 100-kW range.
Henry Keultjes

Fact or theory?

I enjoyed the recent article, (“An evolutionary water heater,” March 1). One thing, however, that doesn't seem to fit in a technical article such as this is your reference to macro evolution as though it were fact. The theories of macro evolution, and especially punctuated equilibrium, are being questioned by more and more scientists, and clearly are far from accepted scientific fact. I think you would do your readers a service when referring to macro evolution to frame it as a theory rather as fact.
John Darjany

The author repsonds: I'm glad you enjoyed the article. I agree with you, macro-evolution is a theory, not a fact. Like the theories of relativity and gravitation, no one can prove these ideas. I would assert that they explain the facts better than anything else humanity has been able to come up with. That doesn't mean they're proven. People are free to reach their own conclusions.
Rich Crouton

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