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"Ed Pawlowski" wrote:
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Sam Takoy wrote:
Hi,
What's the brightness (let's say per foot) of the L.E.D. rope
lights in incandescent-light-watt-equivalent?
Thanks,
Sam
Hi,
Watt is unit of power(energy) There is no such thing as ILWE.
They use a similar rating on the CFLs. GE, for instance, call their
13 Watt bulbs Smart 60.
They really rate bulbs in lumens, but we've used watts for over 100
years so there are a lot of habits to change. I don't know of anyone
that looks at the lumens on the package.
I was talking with a guy the other day, who knows about this stuff in
a way that few do, and he says the only really correct way to compare
light intensity is in watts of *output.* Says lumens aren't a very
clear measure at all. First time I'd heard that, but like I said, the
guy has a boatload of credibility.
Sorry, that doesn't make sense. Watts are units of electrical power
consumption (actually, that should be watts/unit time). For light
output, the unit is lumen. The reason that is a bit misleading is
because the actual energy output is in a subjective manner affected by
the spectral distribution. And that distribution also determines whether
the light is harsh or pleasingly warm. I think the best way to describe
light is as so many lumens at a spectral temperature of so many degrees
(usually expressed in degrees Kelvin). We're just not used to that way
of expressing (yet).
Sorry, but the fellow who told me that is a life-long EE, and one of the
world's leading laser experts. While watts as used in connection with
incandescent lamps has always referred to consumption, the light output
can also apparently be measured in watts. I choose to believe my friend,
whom I've known and respected for 10 years, on this score.
Lasers tend to be rated in watts of output.
This has only very rough correlation with lumens of output.
Output watts or milliwatts are "radiometric", meaning power, or energy
per unit time.
Lumens are "photometric", which takes into consideration a "standard
human eyeball"'s "photopic" spectral response.
One watt of 555 nm yellowish green light is 683 lumens. But, one watt
of 632.8 nm red is about 163 lumens, and 1 watt of 650 nm red is 73 lumens.
1 watt of 685 nm (a longer deep red wavelength of some early visible laser
diodes) is a mere 8 lumens. 1 watt of 405 nm violet is a little over 3
lumens, but looks brighter than that to "night vision" (favoring shorter
visible wavelengths) and causes many fluorescent objects to fluoresce with
as much as 100's of lumens (theoretical limit of 500).
One watt of 532 nm, a common more-luminous green laser wavelength, is
604 lumens. Get a 532 nm laser pointer when you need the most brightness
from the 4.9999 milliwatt limit of Class IIIa - at that wavelength, 4.99
milliwatts is 3 lumens.
One watt of invisible infrared or invisible ultraviolet has zero lumens.
Watt or milliwatt figures for laser output have fairly good correlation
with ability to cause burns, including to irreplaceable photosensors in
the eyes. Lumens has less correlation, since different wavelengths have
greatly different lumens for same watts or milliwatts.
===========
Output of lasers is usually rated in *radiometric* units, as in watts or
milliwatts. Output of lightbulbs is usually rated in *photometric* units,
as in lumens.
--
- Don Klipstein )