It seems like many modern light fixtures say that you should use no more
than a 60-watt bulb. In doing some learning about compact fluorescent
bulbs, I see that a 23 watt CFL provides around the same amount of lumens as
a 100-watt incandescent bulb (1600, compared to 800 lumens from a 60-watt
So it seems like I should be able to replace a 60-watt incandescent bulb
with a 23-watt CFL and get twice as much light, while still staying well
below the fixture's limit of 60 watts... Is that correct?? It somehow
feels like cheating...
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. 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. 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. I recently read
something about micro-LEDs incorporated into wall paint, so a small
current could be applied to a whole wall, which would give off a soft
glow and almost no heat. No telling when or if that will become
practical, but that's probably what people said about hybrid cars a
I almost exclusively use CFLs at home (incandescents for porch/garage,
where cold temps can interfere with most CFLs), and I think they're
definitely the way to go.
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
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.
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:
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
- Don Klipstein ( firstname.lastname@example.org, http://www.misty.com/~don/cfx.html )
That's because there are no significantly marketed general home lighting
LED lightbulbs (equivalent to 40-100 watt incandescent) to get data from.
The most efficient significantly marketed white LEDs (last time I
checked a few weeks ago) are Lumileds "Luxeon" "1 watt" models, with
typical luminous efficacy of 37.6 lumens per watt with chip temperature 25
C, and about 34 lumens/watt typically in the more reasonable condition of
heatsink temperature of 35 C.
LEDs will need a ballast of some kind or another, and losses in that
will result in overall luminous efficacy slightly lower still.
100 watt 120V 750 hour incandescents get 16.7-17.5 lumens/watt, and 60
watt 1000 hour ones get 14-14.8 lumens/watt. Better compact fluorescents
get mostly about 60 lumens/watt.
- Don Klipstein ( email@example.com)
Yes and no.
It is safe to do it, but the heat will likely shorten the life of the CFL.
I read that somewhere...
Just make sure you don't have a dimmer on the circuit unless the bulbs are
designed for dimmers.
yes, but: the widely available compact flourescent bulbs can be used in
open indoor fixtures. at our house we put them into 4 and 5 bulb
ceiling fan fixtures and really brighten up the kitchen and office.
they are not for enclosed fixtures they overheat. read the installation
restrictions on your particular bulb in fine print before you buy.
other types including outdoor styles are available at higher price
ranges. see interesting energy saving stuff like i bought at:
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