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Ask Mr. Tight-Watt: CFL replacement sizes  Smart Choices Archive

Ask Mr. Tight-Watt: CFL replacement sizes

Mr. Tight Watt changes his lightbulbs.

Ask Mr. Tight-Watt

Mr. Tight-Watt got a couple questions about lighting this month. He asked expert Rob Kirkpatrick, Service Concepts, to answer Norman’s questions. Service Concepts is a cooperative that sells energy-efficient lighting and other products to cooperatives.

Question 1 from Norman: I have a light fixture that only allows a 60-watt bulb. If I put in a new CFL bulb, how many watts can I use if I want to get more light?

Answer: Norman, this is a very common question, and the simple answer is easy: Whatever will fit in the fixture, but never higher than the fixture rating (60 watts).

The more detailed answer: The 60-watt limit is typically a fire-hazard limit for incandescent bulbs. It really doesn’t have anything to do with the wattage, per se, but the heat from the bulb. An incandescent bulb converts 90% of the power it consumes into heat and only 10% into light. CFLs use 75% less power to create the same light.

Often, your limit will be defined by the available space in the fixture. The brighter the CFL, the larger it’s likely to be. You may be able to get a 20-watt CFL (75 watts equivalent) in the fixture, and maybe even a 23-watt (100 watt equivalent) - but it may not physically fit.

The two rules of thumb you should keep in mind: 
1. You can use up to a 23-watt (100 equivalent) CFL in an enclosed interior fixture (e.g., a ceiling fixture, if it will fit).
2. Don’t enclose an “enclosed” CFL. That means you can put a bare spiral CFL in an enclosed interior fixture, but do not put a CFL globe light, or “A”-shaped CFL (with an outer glass like the shape of a traditional incandescent bulb) in an enclosed fixture. Without the air circulation they will run warmer and not last as long. And note I said warmer, not hot (see info in the second paragraph about this).


Question 2 from Norman: Can I use fluorescent bulbs in a ceiling fan that has a dimmer switch or do I have to get a special switch?

Answer: Norman, this is an excellent question and really has two parts.

1. Normal compact fluorescent light bulbs should not be used on a dimmer switch. CFLs require full circuit power, and the electronic controls in the ballast will fail early if put on a dimming circuit.  There are special dimmable CFLs available, although more costly and quality can vary. Some folks have asked if it's OK to use CFLs on a dimmer circuit as long as they only use the switch in the full-on or full-off position.  The answer to that is: “It depends,”so the manufacturers generally say “no.” Some dimmer switches allow a small current to flow through even in the off position. You'd never notice with a standard incandescent bulb.  But that will be enough to cause a CFL to go bad prematurely. For this same reason, you shouldn't use a CFL on a circuit with a photo-electric eye. They will often trickle enough power to run the eye, and that's enough to hurt the CFL. Running a CFL on low current would have the same effect as trying to turn the volume down on a stereo by controlling it with a dimming switch. It wouldn't last very long.

2. Some manufacturers will advise you not to use their CFLs in ceiling fans due to the vibration and odd angle they are mounted in.  The manufacturer of the CFLs your cooperative provides do not have this restriction. They may be used in a ceiling fan - as long as it is not on a dimming circuit!

Contact Rob Kirkpatrick: rkirkpatrick@serviceconcepts.coop


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