Compact fluorescent lights: Not always the best solution
Prying Eyes: A look inside a CFL bulb helps explain why they're no good in downward-facing installations.
By Margery Conner, Technical Editor -- EDN, October 30, 2008
After mentioning in a blog post my difficulties with CFLs (compact fluorescent lights) and their tendency to burn out after less than a year of use, I was surprised by the number of comments I received from irate CFL users with similar experiences. It turns out that the lights are not the universal panaceas their developers claimed they would be as replacements for the venerable incandescent light bulbs.
The ideal use for a CFL is in lighting fixtures, such as table lamps, in which the screw-in end is below the unconfined bulb. Sure enough, all but one of my dead CFLs came from enclosed downward-pointing lights with the screw-in end above the heat-generating bulb. In fact, in the whole house, I counted just three upward-pointing, unenclosed lights that would be appropriate for CFLs. Energy Star’s Web site, states that “CFLs perform best in open fixtures that allow airflow, such as table and floor lamps, wall sconces, pendants, and outdoor fixtures” (see Compact Fluorescent Light Bulbs). The Web site also recommends installing CFLs in fixtures that you use at least 15 minutes at a time or several hours per day, which excludes such areas as closets and laundry rooms.
Using an infrared-thermometer gun, I found that the CFL in an enclosed, downward-facing configuration yielded a temperature of 160°F, 40 degrees higher than the table-lamp CFL’s temperature of 120°F and a significant difference that can shorten the bulb’s life.
1. Like any other fluorescent light, a CFL is a gas-discharge tube. It relies on an inductor acting as a ballast to limit the ac current through the tube.
2. Because the inductor would have to be unreasonably large if the CFL operated at the line frequency of 60 Hz, the CFL’s circuitry includes a frequency-multiplier stage relying on several high-voltage transistors; this stage allows for the use of a smaller inductor and smaller current, as well.
3. Compared with an incandescent bulb, a CFL is crammed with electronics. Note the telltale brown stains at the base of the bulb where the CFL overheated.
4. Note the significant amount of hand assembly a CFL requires, both increasing cost and decreasing reliability. All of the wires require hand assembly and soldering.
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When I began my electrical apprenticeship in the late 1970's, the contractor I worked for had to order "base-up" bulbs. Had to do with the position of the bulb in the fixture.
Geprge W. McKinney, Jr. - 2010-22-2 19:07:00 PST -
so what is your complaint
I put them in every location in my house two years ago and droped a 100 watts per month every month after they were installed.
so i have had to replace one or two, repair/replace whats the difference
b traft - 2009-6-4 14:27:00 PDT -
Some of the early Sylvania CFLs had problems, but after improvements and more mfrs making them....what I say from my home use is 5yr av....max 10 years...
Peter Denholm - 2009-6-4 12:30:00 PDT -
The CFL could be produced by hand soldering, but that would be comparably inefficient and more time-consuming than using a wave solderer. If there were marks from overheating, those may have been caused by hand-soldering contacts "missed" by a wave solderer. Was this an off-brand CFL? SOunds like poor quality control.
Joe Simmons - 2009-6-4 12:20:00 PDT -
I have been using CFL's for many years and am very happy with their life. When I get one which seems to have failed prematurely due to a bad ballast, I can sometimes fix it by swapping the ballast from an identical one which has a bad bulb. It isn't easy and probably doesn't save much money, but it is very satisfying to say I fixed that light bulb. They don't have plug-in replacement bulbs for 2 reasons (both money). First, the cost of the plug-in bulbs and sockets is too high. Second, the ballasts aren't designed to last long enough to warrant bulb replacement. A durable ballast would cost too much.
Chris W - 2009-5-3 12:36:00 PST
