I keep it simpler, John. Black is a lack of white (hence the last four
letters in "black"), gray is just a darker shade of white (I've got some
old T-shirts that prove it), and brown is what happens when Roy G. Biv
gets all stirred up.
Have you ever considered the theory that the true purpose of a light
bulb is to suck up darkness? Same thing happens with the sun.
Jim
John M. Steele wrote:
It is not my long suit either. However, I had to learn enough to manage
filtering both electronic displays (native color: cyan VF) and
incandescent instrument panel bulbs (rather low kelvin, yellowish bulbs)
to the corporate lighting color. My guys had trouble understanding why
two very different filters are needed. Two different source spectra,
same end result requires different filters. In fact, with the two
source spectra, and one of the filters, you can spec the other with a
little (lol) math.
The CIE Standard Observer tables are in the CRC Handbook of Chemistry &
Physics, at least in the 43rd and 70th editions, which are the only ones
I have around.
I did not know that women have more cone types than men. But it is
clear my wife can differentiate at least 6!/3! more colors than I can.
My friend Roy G. Biv taught me all the colors i need to know (well,
except black, brown, gray, and white)
------------------------------------------------------------------------
*From:* James R. Frysinger <j...@metricmethods.com>
*To:* U.S. Metric Association <usma@colostate.edu>
*Sent:* Sun, July 11, 2010 5:37:25 PM
*Subject:* [USMA:48178] Re: Light bulbs
John,
Thanks for the correction (where was my head?!) and the excellent
amplification, including the existence of two principle curves, those
being "photopic" (cone, bright light) and "scotopic" (rod, dim light),
with the term "mesopic" used to describe the combined effects of those
in mid-intensity light situations. We might as well point out that the
photopic curve has two "modifications" available that increase its
values a bit near to and into the ultraviolet.
What disenchants me in particular about the CIE curve (esp. the initial
curve of 1924 [date?]) is its pitiful provenance. As I recall, at least
in part, the data for this "visual brightness" curve was taken by
questionable experimental means on 12 (?) "healthy young males" at Yale.
Modern biology tells us that while men (who are not colorblind) possess
three types of cones (based on three receptor molecules), women can
possess as many as six, due to the genes for chromatic development being
on the X chromosome. It's not atypical for a woman to possess at least
four different receptor molecules; I think the "blue-green" one is the
one normally existing in dual form. Thus, it's not entirely cultural
that women can possess finer color sense than men do; they may be
genetically predisposed.
A handful of "healthy young males"?
Your comments about the reluctance of the CIPM to further support
photopic units are appropriate, John.
When I was teaching physics I had my students use the 1931 curve,
following the integration method you described, to calculate the overall
luminous efficacy of incandescent and fluorescent light bulbs (in lumens
per watt). It took me some time to track down the values of that CIE
1931 curve. I seem to recall that incandescent bulbs typically ran about
8 % and fluorescent bulbs closer to 30 % in overall luminous efficacy.
For more information, folks, see
http://www.bipm.org/utils/en/pdf/SIApp2_cd_en.pdf
which exists in electronic form only. The photopic and scotopic curve
values are listed in
http://www.bipm.org/utils/en/pdf/Monographie1983-1.pdf
to which the former link refers.
Again, thanks for the help, John. As you probably sense, photopic
physics is not my long suit.
Jim
John M. Steele wrote:
> That's quite good. However, the maximum luminous efficnecy is 683
lm/W. This is at about 555 nm, and the peak is quite narrow; half power
points are at about 510 nm and 610 nm.
> The CIE is in charge of all things related to light and color
measurement. The basic technique is to multiply the radiometric data by
an action spectrum and integrate. "The standard observer" defines three
such spectra known as the X, Y, and Z tristimulus values. Y is also the
CIE luminosity function. Color is defined in terms of x = X/(X+Y+Z) and
y = Y/(X+Y+Z), there is a z = 1-x-y, but it is usually omitted.
Numerous other color systems are defined relative to these. I belabor
all this to make the point that unless you really love green (555 nm)
light, the value of 683 lm/W is not approachable even theoretically. If
you insist on "white" light, mixing various wavelengths to achieve it,
you get about 1/3 that, perhaps 200-250 lm/W depending on how you define
white, just to get enough wavelengths to approximate white.
> All of that is for our daytime vision. There is another curve for
nighttime vision. Nighttime vision is monochromatic, so only the
alternate luminosity function is defined; the wavelength peak and
sensitivity are different.
> Although photometric units are well established, I think the BIPM
has regrets about being talked into getting into the action spectra
business. Appendix 3 of the SI Brochure makes pretty clear that there
won't be any more as "official SI base units." Human vision could have
been handled as an action spectrum, avoiding the need for the candela
and related units. Keep in mind that other species may have other
action spectra and that the lumen, candela, etc may be useless for
measuring light as perceived by them. It is clearly wrong for plants.
Plants only care about the red and blue, and reflect the green light
which is the basis of luminosity to humans.
> ------------------------------------------------------------------------
> *From:* James R. Frysinger <j...@metricmethods.com
<mailto:j...@metricmethods.com>>
> *To:* U.S. Metric Association <usma@colostate.edu
<mailto:usma@colostate.edu>>
> *Sent:* Sun, July 11, 2010 2:53:43 PM
> *Subject:* [USMA:48175] Re: Light bulbs
>
>
> Those would be low-power light bulbs, not low-energy light bulbs,
Pat. We measure power in watts and energy in joules.
>
> Your question on the seemingly conflicting statements on power (even
more accurately, load) ratings has been very adequately answered.
>
> The issue of spectrum was raised by John Steele. Further to his
excellent observations, it would be appropriate to note that the
determination of the luminous flux of a light bulb is itself
spectrum-dependent. There is a curve of rather arcane derivation that is
used for frequency correction (though it is normally given in terms of
wavelength). The peak of this curve is where the human eye is alleged to
be the most efficient at detecting light and that occurs near 540 THz
(about 555 nm). At this frequency, the luminous efficacy is 643 lm/W.
Away from this frequency, the luminous efficacy factor declines in a
manner that looks vaguely like a bell curve. That is, a stream of
photons at a 1 W power level will be rated as 643 lm. Closer to either
the red or the blue end of the visible spectrum, a stream of photons at
a 1 W power level will be rated at fewer lumens, approaching zero at
frequencies corresponding to 400 nm and 700 nm in vacuum. Those power
levels given in watts are "radiometric" and calculated by multiply the
number of photons per second flowing in the beam by the energy of each
photon (product of Planck's constant and its frequency). The luminous
flux measured in lumens is "photometric". The definition of the lumen,
then, is the meeting point of the radiometric and the photometric camps.
>
> Goodness, I wrote that off the top of my head. Perhaps John can
correct any errors I have made.
>
> Jim
>
> Pat Naughtin wrote:
> > Dear All,
> >
> > Yesterday I went to a hardware store to buy some low-energy light
bulbs. I was shown some bulbs labelled 24 W and I was assured by a sales
assistant that these were 100 W bulbs. What is going on here?
> >
> > Cheers,
> > Pat Naughtin
> > Author of the ebook, /Metrication Leaders Guide,/ see
http://metricationmatters.com/MetricationLeadersGuideInfo.html
> > Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY PO
Box 305 Belmont 3216,
> > Geelong, Australia
> > Phone: 61 3 5241 2008
> >
> > Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that they
now save thousands each year when buying, processing, or selling for
their businesses. Pat provides services and resources for many different
trades, crafts, and professions for commercial, industrial and
government metrication leaders in Asia, Europe, and in the USA. Pat's
clients include the Australian Government, Google, NASA, NIST, and the
metric associations of Canada, the UK, and the USA. See
http://www.metricationmatters.com
<http://www.metricationmatters.com/>for more metrication information,
contact Pat at pat.naugh...@metricationmatters.com
<mailto:pat.naugh...@metricationmatters.com>
<mailto:pat.naugh...@metricationmatters.com
<mailto:pat.naugh...@metricationmatters.com>>
<mailto:pat.naugh...@metricationmatters.com
<mailto:pat.naugh...@metricationmatters.com>
<mailto:pat.naugh...@metricationmatters.com
<mailto:pat.naugh...@metricationmatters.com>>> or to get the free
'/Metrication matters/' newsletter go to:
http://www.metricationmatters.com/newsletter to subscribe.
> >
>
> -- James R. Frysinger
> 632 Stony Point Mountain Road
> Doyle, TN 38559-3030
>
> (C) 931.212.0267
> (H) 931.657.3107
> (F) 931.657.3108
>
-- James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
