Re: If 100W incandescent is 1610lm and 27W CFL is comparable...
- From: don@xxxxxxxxxxxxxx (Don Klipstein)
- Date: Sun, 13 Jan 2008 21:19:04 +0000 (UTC)
In <7c40065c-fd1e-4c3d-b117-9cda1ed8c985@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
itsme.ultimate@xxxxxxxxx wrote:
X-No-Archive: Yes
A 100W incandescent lamp gives off around 1610 lumens and 27W 3000K
tri-phosphor CFL gives about the same as far as what we see.
Now, does a 27W 1600 lumen CFL provide as much light as a 100W
incandescent in the eyes of CCD and film?
Most color digital cameras have sensors whose spectral response is a
rough but reasonable approximation to that of the human eye. They do have
better ability to see infrared than human eyes do, though their infrared
sensitivity is still small. Therefore, if an incandescent and a CFL have
the same light output in photometric terms, their equivalence to human
vision translates to near-equivalence to most color digital cameras.
For most black-and-white CDD security cameras, the story is very
different. Those cameras are generally more sensitive to infrared in the
700-1000 nm band than to visible. When an incandescent lamp and a
non-incandescent white lamp appear equal to the human eye, the
incandescent will appear brighter to a usual black and white CCD camera.
Film tends to see incandescent lamps as slightly brighter than most
non-incandescent lamps when both appear equally bright to the human eye.
Color slide film and color movie film also find most non-incandescent
white lamps to be more blue-greenish than the human eye does. Exceptions
are ones with blackbody-like spectra, such as carbon arcs, xenon arc
lamps, and most xenon strobes.
This effect is milder in the case of fluorescent lamps with very high
color rendering index and a continuous spectrum. This effect is mitigated
with metal halide lamps with whatever rare earth it is that has a very
large number of spectral lines and achieves a fair approximation of
daylight.
The effect on color print film can largely be compensated during
printing.
The explanation for this effect: Human vision has sensitivity
decreasing as wavelength increases through the red region of the spectrum.
However, most film sees the various red wavelengths more equally. Most
non-incandescent white lamps have most of their red/reddish spectral
content towards orange and away from infrared, to maximize the luminous
efficacy (for human vision) of their red/reddish spectral content.
The spectrum has its reddish content mostly at wavelengths where human
vision is more sensitive than film is (for equal "overall red
sensitivity"), and has a shortage of red wavelengths where film is more
sensitive than human vision. So film sees a "red shortage".
Triphosphor fluorescent lamps, including a very large majority of CFLs,
take this to an extreme. A large majority of the red/reddish spectral
content is in a single, extremely narrow band at 611 nm.
- Don Klipstein (don@xxxxxxxxx)
.
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