Several months ago while talking with Cary Eskow ofLightspeed, he mentioned how important it is for the LED lighting industry to carefully frame the applications suitable for solid-state lighting and not try to pretend that LED lights are the perfect lighting solution for every problem. He used the CFL (compact fluorescent light) bulb as an example of hownotto introduce a new lighting product. A variety of agencies, from government to utilities to lighting manufacturers, have presented the CFL as the perfect energy-efficient light source. Homeowners should replace all incandescent bulbs with CFLs; The initial higher price of CFLs was more than offset by its energy savings over its longer life.

There’s been a backlash against CFLs -- especially since the federal law was passed last year that mandates the replacement of all incandescent bulbs by 2012 -- by users complaining that the lights have a shorter life span than advertised. (There’s also concern over CFLs mercury content, but that’s a discussion for another day.)

My personal experience is that CFL lifetime is influenced by its application. Several months ago in a PowerSource  post on dimmer circuits for a CFL I mentioned in passing that I had had poor luck with CFLs burning out early, and several readers commented on their likewise poor CFL lifetimes.

CFLs that are installed in either down lights or ceiling globes in my house have a much shorter life than those installed in a table lamp. A table lamp is probably the most benign environment for a bulb because the heat goes directly up without affecting the CFL bulb's electronics, which are placed in the base. In a down light, the can around the bulb tends to confine the heat to the bulb, causing it to run hotter and I assume shortening its life. Plus, because the bulb in upside down, as the heat rises it makes the bulbs electronics located in the base run hotter than it would in a traditional table lamp configuration.

I shot the temperature of a downlight CFL with an IR gun and got a reading of 160°F at the base, while the table lamp CFL was at 120° F -- a big difference and one that will affect the life of  the electronics in a CFL, including transistors, which don’t like operating at higher junction temperatures.

Here’s a photo of the innards of one of the CFLs that failed: Note the brown, too-hot-looking marks on the plastic base. (If you want to take a part a CFL yourself, I recommend the how-to article at  Instructables .)

 

Like any fluorescent light, a CFL is a gas discharge tube. It relies on an inductor acting as a ballast (the yellow/blue square) to limit the AC current through the tube. Because the inductor would have to be unreasonably large if the CFL operated at the line frequency of 60Hz, the CFL’s circuitry includes a frequency multiplier stage relying on several high-voltage transistors that enable the use of the smaller inductor at the higher frequency.

(Here’s a close-up of the pcb that shows the handwork on these lights that sell (my cost) for about $2. All that handwork means more opportunities for inconsistencies that can lead to increased failure rates.)

If you go to the  Energy Star site, it now has caveats on using CFLs.

“How to Choose and Where to Use CFLs

ENERGY STAR qualified CFLs provide the greatest savings in fixtures that are on for a substantial amount of time each day. At a minimum, ENERGY STAR recommends installing qualified CFLs in fixtures that are used at least 15 minutes at a time or several hours per day.

CFLs perform best in open fixtures that allow airflow, such as table and floor lamps, wall sconces, pendants, and outdoor fixtures.”

In my house I have all of two table/floor lamps that meet Energy Star’s criteria for where CFL’s perform best.

I have to agree with Eskow that the CFL proponents have done a poor job of setting the stage for CFLs as a universal replacement for incandescents. If CFLs have a shorter life in some applications and should be selected with care, or specialized versions should be used, then that information should be made clear and emphasized.

In the meantime, I use CFLs where they are appropriate, and I look forward to LED lighting that both sips power and has virtually no pollution.