Eeyore said:
Well, they *are* dimmer than conventional incandescents.
I've always found the idea that they use 1/5 the power
misleading. Those comparisons were made with 'softone'
bulbs.
You need at least a 23W CFL to match the output of a 100W
incandescent.
The table here...
http://en.wikipedia.org/wiki/Incandescent_lamp#Power
Shows a 100W incandescent providing 1700 lumens.
In comparison some new CFLs I have claim only 1100 lumens
for an 18W and 1200 lumens for a 20W.
The 11W CFLs claim 600 lumens and that makes them only
slightly brighter than a standard 40W bulb instead of
equivalent to a 60W as claimed.
My searching finds ordinary 40 watt bulbs rated at from 280 to 355 lumens.
More lumens at a given wattage rating generally means a shorter life. IME
incadescent lights draw significantly less than their rated power, so their
light output may also be less than spec.
280 to 355 lumens is about half the light output of a 11 watt CFL. BTW, my
experience with CFLs pretty well matches the lumen output levels that you've
mentioned, Graham.
About twice the brightness from about one quarter the power works for me!
We've seen vastly improved bulb life, which is especially helpful when bulbs
are located where they are hard to replace, such as at the top of a 3-story
stairwell.
My first project was in a large basement room that was frying about one
halogen bulb (of 32) per week, partially due to overheated fixtures. We
pretty much relamped the room almost twice a year. We put in 2 CFL bulbs
per fixture and still dropped the fixture's internal temperature to under
110 degrees F from more like 140. Lumen output per fixture almost tripled.
We were also able to get a more pleasing color temperature. This room is has
been relamped for about 3 years. We are currently replacing about one bulb
per year.
I've done a fair number of fairly large (i.e., 8 or more bulbs per room)
incadescent (mostly halogen) to CFL upgrades, with extremely positive
results. In every case the fixtures were previously loaded up with
incadescent bulbs rated at the fixture's maximum power. They were providing
poor to marginal lighting.
When I can maintain the power usage at a constant level, the results of the
CFL upgrades are brilliant. When I'm forced to run the fixture at reduced
power levels because of bulb space limitations, the results are still
striking and very helpful.
The building in question had lighting engineered to 1950's standards. The
lighting had become ineffective because of rising expectations. Actually
upgrading the fixtures would have been prohibitively expensive.