Compact fluorescent lights: Not always the best solution

Tag : inductor
Feature Compact fluorescent lights: Not always the best solution Prying Eyes: A look inside a CFL bulb helps explain why they're nogood in downward-facing installations. By Margery Conner, Technical Editor -- EDN, 10/30/2008
After mentioning in a PowerSource blog post my difficulties with CFLs (compact fluorescent lights) and theirtendency to burn out after less than a year of use, I was surprisedby the number of comments I received from irate CFL users with similar experiences. It turnsout that the lights are not the universal panaceas their developersclaimed they would be as replacements for the venerableincandescent light bulbs.
The ideal use for a CFL is in lighting fixtures, such as tablelamps, in which the screw-in end is below the unconfined bulb. Sureenough, all but one of my dead CFLs came from encloseddownward-pointing lights with the screw-in end above theheat-generating bulb. In fact, in the whole house, I counted justthree upward-pointing, unenclosed lights that would be appropriatefor CFLs. Energy Star’s Web site, states that “CFLs perform best in open fixturesthat 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 thatyou 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 anenclosed, downward-facing configuration yielded a temperature of160°F, 40 degrees higher than the table-lamp CFL’stemperature of 120°F and a significant difference that canshorten 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 accurrent through the tube.
2. Because the inductor would have to be unreasonably large if theCFL operated at the line frequency of 60 Hz, the CFL’scircuitry includes a frequency-multiplier stage relying on severalhigh-voltage transistors; this stage allows for the use of asmaller inductor and smaller current, as well.
3. Compared with an incandescent bulb, a CFL is crammed withelectronics. Note the telltale brown stains at the base of the bulbwhere the CFL overheated.
4. Note the significant amount of hand assembly a CFL requires, bothincreasing cost and decreasing reliability. All of the wiresrequire hand assembly and soldering.