In article . com,
wrote:

Yep - if it says 23 watts, that's all it's using. With incandescent
bulbs, most of that 100 watts (about 97 percent of the energy, IIRC) is
just turned into heat.

Generally 93-95%.

CFLs are obviously more efficient, turning more
of the energy into light instead of heat. As you pointed out, they're
about 4 times more efficient (1/4 the wattage for roughly the same
light output), so you're still only getting about 90% of the electrical
energy turned into light, but it's a lot better.

Better CF lamps are about 20% efficient at producing light, and the
light is mostly of wavelengths selected for the human eye to be more
sensitive to - which is why better ones have 4 times the luminous efficacy
of incandescents when they are closer to 3 times as efficient at converting
electricity to visible light.

So CF lamps are about 80% efficient at producing heat.

Actually, when it comes to heating the room, all lamps are closer to
100% efficient at producing heat, since most of the light will be absorbed
in the room.

One thing to keep in mind: About half the energy going into an
incandescent becomes infrared that passes through the glass, and
presumably escapes the fixture as well as visible light does, and this is
heat materializing in the room but not the fixture. So incandescents are
generally around or somewhat under 50% efficient at producing heat that
turns up in the fixture. Compact fluorescents are about 80% efficient at
producing non-radiant heat - nearly twice as efficient as incandescents at
heating up fixtures.
Because of this, I would not use compact fluorescents of more than half
the maximum wattage for a fixture that has a rated maximum wattage for
incandescent lamps.

Now for another bug in some fixtures: Compact fluorescents are more
sensitive to heat than incandescents are. Even if the fixture does not
overheat, a higher wattage compact fluorescent can overheat in a small
enclosed fixture or a downward-facing fixture. This is mostly a problem
with compact fluorescents of wattage 20 watts or more.
The Philips SLS 15, 20, and non-dimmable 23 watt (but not the 25 watt
nor the dimmable 23 watt nor non-SLS models) are actually rated to
withstand the heat buildup in recessed ceiling fixtures.

And the color and warm-up time of CFLs has increased dramatically over
the last few years, while price has decreased. I've gotten them on sale
at Home Depot etc. for about $10 for a pack of 4, and some electric
companies have rebates.

LEDs are the next step - not many available for home use yet that I
know of, (more in flashlights etc), but they're somewhere around 10-15
times more efficient than incandescents.

The best white LEDs on the market now have efficiency 2-3 times that
of incandescents. There has been a lot of hype and half-truths about the
efficiency of LEDs. In some specific applications other than household
lighting, especially traffic lights, LEDs outperform incandescents in
efficiency by a much larger margin.
Details are in a web file of mine:

http://www.misty.com/~don/lede.html

Expect it to be quite a few years before LEDs are used to make regular
household lightbulbs. For one thing, compact fluorescents are still more
efficient than LEDs. For another, LEDs are prohibitively expensive for
such use - with 1.2 watt LEDs costing a few dollars apiece. Another
obstacle with high power LEDs is heat output - they are still 85 efficient
at producing non-radiant heat and generally do not take heat well.

Meanwhile, I agree that compact fluorescent is the way to go in most
applications.

- Don Klipstein , http://www.misty.com/~don/cfx.html)