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[DSLF] Digest Number 574
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There are 13 messages in this issue.
Topics in this digest:
1. deer and moose
From: Susan Harder <lookout@hamptons...>
2. Re: Lighting cost calculator
From: Tim Poulsen <poulsen@netacc...>
3. Re: deer and moose
From: Anthony Arrigo <Anthony.Arrigo@CampusPipeline...>
4. Re: NY veto
From: Steve Davis <w2sgd@juno...>
5. Re: A few things we should know about light pollution!
From: "Fabio Falchi" <fabio.falchi@libero...>
6. Italian flap
From: Steve Pauley <spauley@cox-internet...>
7. Small victory in Idaho
From: Steve Pauley <spauley@cox-internet...>
8. Re: Small victory in Idaho
From: ctstarwchr@aol...
9. Re: Re: A few things we should know about light pollution!
From: "David Keith" <keithd@resodance...>
10. R: A few things we should know about light pollution!
From: "Pierantonio Cinzano" <info@inquinamentoluminoso...>
11. Re: Re: Lighting cost calculator
From: "Terry McGowan" <lighting@ieee...>
12. Guidelines For Minimizing Skyglow
From: "ctstarwchr" <ctstarwchr@aol...>
13. Re: R: A few things we should know about light pollution!
From: Yvan Dutil <yvan.dutil@sympatico...>
________________________________________________________________________
________________________________________________________________________
Message: 1
Date: Wed, 06 Feb 2002 06:52:45 -0500
From: Susan Harder <lookout@hamptons...>
Subject: deer and moose
All,
There is an extremely high population of deer on the island of North Haven, NY (you may
have seen it featured on Sixty Minutes-CBS, Steve Kroft lives here). Recently they
installed the in ground reflectors on the sides of the road and one down the middle,
instead of overhead street lights. Not only is there great visibility of the distant
twists and turns in the road, but I am better able to see the deer, all because my
headlights are allowed to do their job instead of competing with streetlight glare. The
reflection in the Deer's eyes is especially visible. Plus I put the $7 "whistles" on the
front bumper of my car, which makes them stand still. I've heard that these reflectors
will be torn up by snow plows, so this may not be a good choice for Alaska, but southern
climes could benefit.
Susan Harder
East Hampton
________________________________________________________________________
________________________________________________________________________
Message: 2
Date: Wed, 06 Feb 2002 09:59:54 -0500
From: Tim Poulsen <poulsen@netacc...>
Subject: Re: Lighting cost calculator
"Kirke Coney" <kirkec@austin....com> wrote:
> Fluorescent is misspelled. The lumen outputs are not familiar to me
> (e.g. 400HPS is listed at 45,000 lumens, not 50,000), but that may
> not be significant. Pulse start metal halides would be a good
> addition. I like the format a lot.
Kirke,
Thanks for catching the misspelling. I got the lumen figures (as well as
the wattages) from an IDA info sheet and cross-checked a handful with
some product literature (GE's I believe). The incandescent figures came
off some light bulb packages laying around my house.
I'm not familiar with the pulse start MH lights. I assume they just use
a different ballasting system, right? So the lamp wattages would be the
same but the circuit wattages would be less/more. Correct? If you know
where I can find some of that information, I will be happy to add them
to the list.
Thanks,
Tim
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Message: 3
Date: Wed, 06 Feb 2002 07:35:16 -0700
From: Anthony Arrigo <Anthony.Arrigo@CampusPipeline...>
Subject: Re: deer and moose
Great idea!
Use the least expensive approach to problem solving...
More people ought to explore that route first.
As for troubles in northern areas... I've seen these things installed in a recessed manner.
This is more expensive that surface mounted, but... a heck of a lot cheaper to install than
installing a roadway lighting system. And...there are virtually no ongoing costs... like
electricity.
APA
Susan Harder wrote:
> All,
>
> Recently they installed the in ground reflectors on the sides of the road and one down the
> middle, instead of overhead street lights. Not only is there great visibility of the
> distant twists and turns in the road, but I am better able to see the deer, all because my
> headlights are allowed to do their job instead of competing with streetlight glare. The
> reflection in the Deer's eyes is especially visible. ...
> I've heard that these reflectors will be torn up by snow plows, so this may not be a good
> choice for Alaska,
________________________________________________________________________
________________________________________________________________________
Message: 4
Date: Wed, 6 Feb 2002 10:07:59 -0500
From: Steve Davis <w2sgd@juno...>
Subject: Re: NY veto
Fabio Falchi wrote:
> Isn't it possible to sue the Governor for the added
> cost that NYS will pay doing BAU in outdoor practices
> vs. the economy of the FCO fixtures?
> Perhaps it is a fool idea, but...who knows
Maybe not the governor directly, but it is possible.
Article 87 may be one avenue. Another would be
not performing sworn duties as defined by the
state constitution. Any volunteer lawyers?
Use http://161.11.3.75/ to roast a pig. -sd
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Message: 5
Date: Wed, 6 Feb 2002 16:42:59 +0100
From: "Fabio Falchi" <fabio.falchi@libero...>
Subject: Re: A few things we should know about light pollution!
Dear Yvan,
perhaps I misunderstand what you're telling us, but your analisys show that
the way to go is FCO, not CO.
Let's compare two fixtures, a prismatic CO vs a FCO. The CO emits about 3%
directly above the horizon while the FCO emits zero. Assuming a 15% albedo
we get:
CO: 15*0.29+3*0.795=6.74
FCO: 15%*0.29+0=4.35
To pollute more than CO, we need to install 55% more FCO fixtures than CO
ones. There is a lot of room to spare, even if we put the fixtures closer to
maintain uniformity. This need to closer spacing is due not to the
requirement of zero light above the horizon, but to limitation in intensity
at low angles under the horizon.
We should introduce a definition of fixture with zero emission above the
horizon but with no limitation under it. Call it SKY CUT OFF?
Fabio Falchi
________________________________________________________________________
________________________________________________________________________
Message: 6
Date: Wed, 06 Feb 2002 09:18:25 -0700
From: Steve Pauley <spauley@cox-internet...>
Subject: Italian flap
Are these traitors radio astronomers?
If not.... follow the money.
Steve P
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________________________________________________________________________
Message: 7
Date: Wed, 06 Feb 2002 10:22:51 -0700
From: Steve Pauley <spauley@cox-internet...>
Subject: Small victory in Idaho
Another small victory:
The Hailey, ID Planning and Zoning passed a light
pollution ordinance last night and sent it on to the
Hailey City Council. The proposed ord. is even
better than Ketchum's.
Hailey is 12 miles south of Ketchum, and
has a population of 5500.
http://www.pe.net/~rksnow/idcountyhailey.htm
Steve Pauley
________________________________________________________________________
________________________________________________________________________
Message: 8
Date: Wed, 06 Feb 2002 13:09:29 EST
From: ctstarwchr@aol...
Subject: Re: Small victory in Idaho
In a message dated Wed, 6 Feb 2002 12:27:45 PM Eastern Standard
Time, Steve Pauley <spauley@cox-internet...> writes:
> The Hailey, ID Planning and Zoning passed a light
> pollution ordinance last night and sent it on to the
> Hailey City Council. The proposed ord. is even
> better than Ketchum's.
>
Wow! Congratulations on your hard work Steve! Now, what is
Ketchum going to do now so they can *catch em* ??? ;-)
Please send me a copy directly so we can add it to the listings.
Thanks!
Clear skies,
Cliff Haas
________________________________________________________________________
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Message: 9
Date: Wed, 6 Feb 2002 12:28:34 -0700
From: "David Keith" <keithd@resodance...>
Subject: Re: Re: A few things we should know about light pollution!
To speak just to the last statement: I expect that in Tuscon in March the
IESNA Roadway Lighting Committee will be discussing possible revisions to
"its" luminaire classifications - including separating the intensity limits
of the current cutoff classification from a new - additional and separate -
classification based on "lumens above horizontal".
I am working on a presentation for that meeting about the correlation
between "unit uplight density" and a classification (proposed by J. Bullough
of LRC) which counts initial lumens above horizontal and relates them to the
rated lamp lumens. The boundaries are at "over 0%", 5%, 10% and 20% - so
there are five categories in theory. So far I am just using letters to
identify the different classifications. Names and/or initials for
identification would be appropriate (but I would recommend that the word
"cutoff" not be included - I was considering U0, U5, U10 and U20.) I expect
to put this presentation onto the web when done.
David Keith
----- Original Message -----
From: "Fabio Falchi" <fabio.falchi@libero...>
To: <DarkSky-list@yahoogroups...>
Sent: Wednesday, February 06, 2002 8:42 AM
Subject: [DSLF] Re: A few things we should know about light pollution!
>
> Dear Yvan,
> perhaps I misunderstand what you're telling us, but your analisys show
that
> the way to go is FCO, not CO.
> Let's compare two fixtures, a prismatic CO vs a FCO. The CO emits about 3%
> directly above the horizon while the FCO emits zero. Assuming a 15% albedo
> we get:
> CO: 15*0.29+3*0.795=6.74
> FCO: 15%*0.29+0=4.35
> To pollute more than CO, we need to install 55% more FCO fixtures than CO
> ones. There is a lot of room to spare, even if we put the fixtures closer
to
> maintain uniformity. This need to closer spacing is due not to the
> requirement of zero light above the horizon, but to limitation in
intensity
> at low angles under the horizon.
> We should introduce a definition of fixture with zero emission above the
> horizon but with no limitation under it. Call it SKY CUT OFF?
>
> Fabio Falchi
________________________________________________________________________
________________________________________________________________________
Message: 10
Date: Wed, 6 Feb 2002 22:07:33 +0100
From: "Pierantonio Cinzano" <info@inquinamentoluminoso...>
Subject: R: A few things we should know about light pollution!
Dear Ivan,
it is good that a paper make clear that a lumen of light spilled near the
horizon pollute about three times than the same lumen diffused on the
asphalt. In countries like Europe where the CIE-C2 alphalt with a smaller
albedo is used extensively, you might find even greater factors.
Your paper looks very interesting and I will be happy to read it. Nice work!
However, assuming that I understood well your resume, I do not agree with
your final conclusions. It seems to me that you missed two important points
commenting about full cut-off.
You wrote:
<If we used a standard albedo of 15% for the
<pavement, it can be shown that the reflected light will dominate the
<pollution budget if the light emitted directly above the horizon does not
<exceed 5.5%! This would means that simple cut-off optics would produce
<less light pollution since they only emit 2% of their light above horizon.
If we want minimizing light pollution, the pollution produced by light
emitted directly above the horizon must be very small or negligible in
respect to the pollution due to reflexion by lighted surface (which is
necessary to the lighting process). If they are equal for a fixture with an
upward flux of 5.5% and if we want reduce the direct pollution at least at
1/10 of the reflected pollution, then we need fixtures emitting less than
0.55% of upward flux. This means that semi-cut-off fixtures are ruled out
and you need full cut off.
Moreover take into account that it is important not only the "total
pollution budget" but also the ratio direct versus reflected light at
different elevation angles.
As the cited paper Cinzano-Diaz Castro showed, the emission at small
elevations (under 45 degrees) is responsible for almost all the artificial
sky brightness at zenith outside few kilometers from the sources
(http://debora.pd.astro.it/cinzano/papers.html). This means that small
angles emission is a main source of the artificial brightness in the
country, in astronomical sites outside cities, and sometime also inside
towns when they are located in densely populated areas.
At small elevations the Lambertian emission from surfaces is very small so
the pollution is due almost completely to direct light from fixtures.
Minimizing direct pollution in respect to reflected pollution at small
angles requires limits much smaller than the 0.5% cited above. You
necessarily need very good full-cut-off fixtures.
The demonstrations by light engineers that "with less stringent optical
cutoff, the poles can be more spaced for a same uniformity and the overall
fraction of light that goes up, including the ground reflection, can be
reduce by up to 20%" are wrong (or misunderstood)for this and for many other
reasons, some of which I explained clearly at the CIE TC4-21 meeting in
Athens. Probably at New York nobody sufficiently expert to demolish the
wrong thesis of light polluters has been consulted by politicians. In any
case it looks like the Governor was in touch with them.
The point is that you must minimize not only the total pollution, which is
an integrated parameter, but also this ratio at any angle. In fact the
Lumbardy Law in Italy does not limit the upward flux ratio, which is an
integrated quantity, but it limit the upward intensity per unit flux (which
depends on the angle) at any angle over the horizon. And there are no limits
at all under the horizon.
Cheers,
Pierantonio
------------------------------------------------------------------
PIERANTONIO CINZANO
Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso - ISTIL
Light Pollution Science and Technology Institute
e-mail: cinzano@inquinamentoluminoso...
cinzano@lightpollution...
web: http://www.pd.astro.it/cinzano/
http://www.inquinamentoluminoso.it
http://www.lightpollution.it/dmsp/
http://www.istil.it
------------------------------------------------------------------
-------------------------------------------------------------------------
PIERANTONIO CINZANO
International Dark-Sky Association - Italia
Direttore Scientifico
e-mail: cinzano@inquinamentoluminoso...
web: http://www.inquinamentoluminoso.it
------------------------------------------------------------------------
-----Messaggio originale-----
Da: Yvan Dutil [mailto:yvan.dutil@sympatico...]
Inviato: mercoledì 6 febbraio 2002 2.06
A: DarkSky-list@yahoogroups...
Oggetto: [DSLF] A few things we should know about light pollution!
This a text I have prepare for the next dark-sky newsletter. Unfortunately,
due to a lack of place,
we will have to wait up to next edition to have it publish. Meanwhile, I
will
have probably publish
my research paper in PASP. By the way, I am open to any comment.
Yvan Dutil
----------------------------------------------------------------------------
----------
Recently, two major legislations against light pollution have been rejected.
One in the New York state, the other in the Czech Republic, One of the
reasons invoked was lack of scientific justification for full cut-off lamp.
Arguments invoked by astronomers (light above the horizon=pollution)
backfired in face of analysis done by lighting engineers demonstrating that
with less stringent optical cutoff, the poles can be more spaced for a same
uniformity and the overall fraction of light that goes up, including the
ground reflection, can be reduce by up to 20% (Remande 2000). Unfortunately,
these two conflicting conclusions are based on simplistic model of the light
pollution. Our understanding of the light pollution must improve otherwise
the same scenario will repeat again.
Common sense is that up-going light equals light pollution. The classical
example is an old fashion lamp that emits directly 35% of the light up, 65%
down of which 10% is reflected up. Overall, 45% of the light ends up
illuminating the sky. Then with full cut-off optics, the direct emitted
light
goes down to 0%, and only the light reflected on the ground goes up, 10%. In
consequence, we would expect a spectacular 88% in reduction of the overall
pollution. Lighting engineer got even further, by following the engineering
norms and applying their model for road illumination, they came down to the
conclusion that light pollution can be minimized of you use semi-cutoff
optics, which allows a few percents of light to spill above the horizon.
Unfortunately, this model does not take account of a very simple fact: light
emitted at low angle is more polluting that light emitted at the vertical.
Simply, there is more air in the direction of the horizon than at the
zenith,
which provide more chance for a photon to get diffused. Don’t forget, that
in
essence light pollution is not a problem of light going up but a problem of
light that was going up but got diffused on the ground. In consequence, it
has been shown up by Pierantiono Cinzano & Francisco Javier Diaz Castro,
that
most of the light pollution is produce by light emitted at angle below 10
degrees above the horizon. Unfortunately, the results of this key paper are
presented in a form that renders them impractical for engineering practice.
In order, to address this issue I have develop a simple model of atmospheric
diffusion (Dutil 2002). It is essentially the same model as the one develop
by Garstang and use recently by Cinzano et al. to produce their world atlas
of light pollution. With some simplifications that ease the calculation but
have little impact on the final result.
For typical atmospheric condition, the light pollution efficiency peaks at 4
degrees above the horizon at a value 5.85 times higher than at zenith.
However order to evaluate the real impact of the light pollution, we have to
sum the contribution of every angles. I have examined three typical emission
functions: uniform over 10 first degrees above horizon (spilled light from a
good lamp), lambertian (like a reflection on pavement) and uniform (like the
emission of a globe). The pollution coefficients for each distribution are
respectively 0.7950, 0.2902 and 0.4206. From these numbers we can deduce
that a lumen of light spilled near the horizon pollution 2.74 more than the
same lumen diffused on the asphalt, and 1.89 times more that if it was
emitted by an infamous globe! Readers have to be advised that this result
have not been peer reviewed yet and in consequence should be use with great
care.
What does this means in practice? If we used a standard albedo of 15% for
the
pavement, it can be shown that the reflected light will dominate the
pollution budget if the light emitted directly above the horizon does not
exceed 5.5%! Taken at face value this would means that lighting engineers
are
right and that simple cut-off optics would produce less light pollution
since
the only emit 2% of their light above horizon. If we recalculate the
previous
example with those number, we get: 35%+10%/2.74=38.65% vs 10%/2.74=3.65%. As
we can see, the real reduction of light pollution is 90.6% instead of 88% as
we have previously calculated.
Is this the end of the full cut-off lamp? Nothing is less sure. First, we
need to take account of the real amount of light spilled by lamp. Lamps are
rarely exactly level and this inevitably increasing the light loss. This
factor alone is enough to favor full cut-off optics. Second, the claims of
engineers are based on a requirement of illumination uniformity. Real night
vision is more complex and rigorous modeling with probably end up with a
different result, especially if glare is taken into account.
Do not forget that better lighting practice is our ultimate goal. Once the
physics is well understood, optimization is easy.
Reference:
Cinzano, P., Diaz Castro, F. J., 2000, Mem. Soc. Astro. It., 71, 251
Cinzano, P., Falchi, F., & Elvidge, C. D. 2001, Monthly Notices of the Royal
Astronomical Society, 328, 689
Dutil, Y., to be submitted to Publication of the Astronomical Society of the
Pacific
Garstang, R. H. 1986, Publication of the Astronomical Society of the
Pacific,
98, 364
Garstang, R. H. 1989, Publication of the Astronomical Society of the
Pacific,
101, 306
Garstang, R.H. 1991, Publication of the Astronomical Society of the Pacific,
103, 1109
Remande, C., 2001, in Preserving the Astronomical Sky, IAU Symposium, Vol.
196, R. J. Cohen and W. T. Sullivan, III, eds.
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Message: 11
Date: Wed, 6 Feb 2002 12:18:00 -0500
From: "Terry McGowan" <lighting@ieee...>
Subject: Re: Re: Lighting cost calculator
Tim, the "Pulse Start" metal halide technology is rapidly replacing the older metal halide systems because of longer lamp life, higher efficacy, and improved color stability. The basic difference is that the pulse-start lamp has two electrodes rather than three. That means a different ballast, or at least one with a starting circuit added, is required. All of the major lamp manufacturers make the pulse-start lamps. Venture has a particularly broad line listed.
You're probably better to use the manufacturers' lamp ratings since ratings have been changing and I don't know the age of the IDA sheet. Table 6-9 in the "Advanced Lighting Guidelines - 2001" is an average of several manufacturers' data and should still be O.K. (the ALG can be downloaded from http://www.newbuildings.org ). Circuit wattages and efficacies for all of the energy-efficient HID systems are listed in Table 6-10 for both initial and mean lamp light output.
Terry McGowan
----- Original Message -----
From: Tim Poulsen
To: Darksky list
Sent: Wednesday, February 06, 2002 9:59 AM
Subject: [DSLF] Re: Lighting cost calculator
Thanks for catching the misspelling. I got the lumen figures (as well as
the wattages) from an IDA info sheet and cross-checked a handful with
some product literature (GE's I believe). The incandescent figures came
off some light bulb packages laying around my house.
I'm not familiar with the pulse start MH lights. I assume they just use
a different ballasting system, right? So the lamp wattages would be the
same but the circuit wattages would be less/more. Correct? If you know
where I can find some of that information, I will be happy to add them
to the list.
________________________________________________________________________
________________________________________________________________________
Message: 12
Date: Thu, 07 Feb 2002 01:59:01 -0000
From: "ctstarwchr" <ctstarwchr@aol...>
Subject: Guidelines For Minimizing Skyglow
The CIE offers a document titled, "Guidelines For Minimizing Sky Glow"
CIE 126-1997
ISBN 3 900 734 83 6
A refreshing recommendation by the CIE is considerably bolder than
what is published by the IES regarding lighting levels. They
recommend always using the MINIMUM specified levels "unless the
specific installation requires relaxation."
One conundrum still prevails and has since the very beginning between
IESNA and CIE where vertical candela cutoff angle classifications are
concerned. Before the IES considers redefining the wheel once again
perhaps members on the deciding committees would bode well to
research what their predecessor the CIE already recognizes and
achieve some form of consensus.
* IES cutoff and CIE cutoff classifications don't match
* IES semi-cutoff and CIE semi-cutoff classifications don't match
* CIE does not recognize full cutoff classification
* Neither CIE nor IES recognizes Sharp Cutoff classification
With the IES being recognized primarily in the US and recently in New
Zealand and parts of Australia with the new chapter formed there last
year, they only cover a small portion of real estate, however, the
luminaire manufacturers who service a global market need UNIVERSAL
language to *properly* describe their products to the consumers,
illuminating engineers, and lighting designers!
In the case of American luminaire manufacturers who supply the global
market, numerous luminaires that are presently listed as only meeting
*cutoff* specifications actually meet and sometimes exceed the IES
FCO specifications. However, due to well meaning people who write
ordinances REQUIRING FCO luminaires, many of those fine products may
not be allowed after a site plan review is performed if the reviewer
does not fully understand how to properly interpret photometric
reports. Adding to that perplexing problem usually performed by
laymen with no formal training, photometry is not always reported to
any universal standard in marketing or engineering literature
either. Adding to that problem, IES data reports resulting from
certified goniophotometer analysis are often very difficult if not
impossible to attain as well. Where does that leave us? Is this
beneficial? When comprehensive data is available yes, but that is
often not the case.
With one global language universally accepted between the IES and the
CIE, lighting manufacturers can finally stop trying to rob Peter to
pay Paul and list in their marketing literature this product meets
*x* cutoff classification and it will actually MEAN something that
everyone can trust and clearly understand. Food for thought.
Clear skies and good seeing,
Keep looking up!
Cliff Haas
Member IESNA
http://members.aol.com/ctstarwchr
________________________________________________________________________
________________________________________________________________________
Message: 13
Date: Wed, 06 Feb 2002 21:36:25 -0500
From: Yvan Dutil <yvan.dutil@sympatico...>
Subject: Re: R: A few things we should know about light pollution!
Pierantonio Cinzano a écrit :
> Dear Ivan,
>
> it is good that a paper make clear that a lumen of light spilled near the
> horizon pollute about three times than the same lumen diffused on the
> asphalt.
Yes, I was happy to see than Jan Hollan got similar result with his own
program.
> In countries like Europe where the CIE-C2 alphalt with a smaller
> albedo is used extensively, you might find even greater factors.
Good comment. I have first plan to used the real BRDF of asphalt unfortunately
the form used by the CIE neglected the two angles that are to most inportant
for light pollution calculation. I would be very happy if someone could find
the original data at the base of the CIE definition and just process them in
table not optimized for road lighting application but for astronomy. As you
have mention in a couple of paper, there is a specular component in the
reflected light. Even witout knowing the real illumination function of lamp
it is very likely this will increase push more light near the zenith than a
lambertian
reflection. The would mean that we overestiamet the light pollution produce
be the reflection.
>
> Your paper looks very interesting and I will be happy to read it. Nice work!
You havent read yet for two reasons: it is not yet finish and I estimate there
is
something like 50% of chance that you will be the referee.
> However, assuming that I understood well your resume, I do not agree with
> your final conclusions. It seems to me that you missed two important points
> commenting about full cut-off.
>
> You wrote:
> <If we used a standard albedo of 15% for the
> <pavement, it can be shown that the reflected light will dominate the
> <pollution budget if the light emitted directly above the horizon does not
> <exceed 5.5%! This would means that simple cut-off optics would produce
> <less light pollution since they only emit 2% of their light above horizon.
>
> If we want minimizing light pollution, the pollution produced by light
> emitted directly above the horizon must be very small or negligible in
> respect to the pollution due to reflexion by lighted surface (which is
> necessary to the lighting process). If they are equal for a fixture with an
> upward flux of 5.5% and if we want reduce the direct pollution at least at
> 1/10 of the reflected pollution, then we need fixtures emitting less than
> 0.55% of upward flux. This means that semi-cut-off fixtures are ruled out
> and you need full cut off.
>
I think it should be 1/10 of 15% in this case about (1.5%). Anyway, cut-off
optics are unlikely to achived that performance. I think that Duco Schreuder
set up at 2% the error on measurement of ULOR from a lamp. Also as I
pointed out mis-align optics will have larger ULOR than stated from the lab
condition. I recentely read a paper that claim the typical mis-aligment is abour
+-5 degres. This translate in many percent of error in the ULOR. By the way,
is anyone have the official definition for CO, FCO and SCO? They seam to
be conflicting information.
>
> Moreover take into account that it is important not only the "total
> pollution budget" but also the ratio direct versus reflected light at
> different elevation angles.
>
> As the cited paper Cinzano-Diaz Castro showed, the emission at small
> elevations (under 45 degrees) is responsible for almost all the artificial
> sky brightness at zenith outside few kilometers from the sources
> (http://debora.pd.astro.it/cinzano/papers.html). This means that small
> angles emission is a main source of the artificial brightness in the
> country, in astronomical sites outside cities, and sometime also inside
> towns when they are located in densely populated areas.
I have hesited before going for the total light pollution as an indicator.
The key argument that convinced me is that most of the diffused
light lands far from the emitting source. In consequence, the total light
pollution is strongly dominated by the light emitted at low angles. The
other argument is that in most develloped regions the density of population
is such that there is almost always a light source within 5-10 km putting
more weight on high angles in not such a bad thing. The last point is that
I have sacrified the capability to calculate the variation with the distance
in order to simplify the calculation. Anyway, I have not done yet the
comparison between my model and your result for far sources they may
not differ that much after all.
>
> At small elevations the Lambertian emission from surfaces is very small so
> the pollution is due almost completely to direct light from fixtures.
> Minimizing direct pollution in respect to reflected pollution at small
> angles requires limits much smaller than the 0.5% cited above. You
> necessarily need very good full-cut-off fixtures.
My calculation for lambertian surface take account of this effect.
>
> The demonstrations by light engineers that "with less stringent optical
> cutoff, the poles can be more spaced for a same uniformity and the overall
> fraction of light that goes up, including the ground reflection, can be
> reduce by up to 20%" are wrong (or misunderstood)for this and for many other
> reasons, some of which I explained clearly at the CIE TC4-21 meeting in
> Athens. Probably at New York nobody sufficiently expert to demolish the
> wrong thesis of light polluters has been consulted by politicians. In any
> case it looks like the Governor was in touch with them.
I must say that this is a VERY comment idea in the lighting industry. Even
people from Lumec-Schréder in Québec, who are very against light
pollution put this information in their information sheet. That's why it is so
important to adresse this issue.
However, from the data I have in hand, I have been unable to demonstrate that
the calculation of Remande (2000) are wrong. This bother me since I expected
more difference but essentialy his result even corrected for the angular effects
still facour semi-cuttof optics? Maybe, I made a error in my calculation
somewhere.
>
> The point is that you must minimize not only the total pollution, which is
> an integrated parameter, but also this ratio at any angle. In fact the
> Lumbardy Law in Italy does not limit the upward flux ratio, which is an
> integrated quantity, but it limit the upward intensity per unit flux (which
> depends on the angle) at any angle over the horizon. And there are no limits
> at all under the horizon.
>
> Cheers,
>
> Pierantonio
>
> ------------------------------------------------------------------
> PIERANTONIO CINZANO
> Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso - ISTIL
> Light Pollution Science and Technology Institute
> e-mail: cinzano@inquinamentoluminoso...
> cinzano@lightpollution...
> web: http://www.pd.astro.it/cinzano/
> http://www.inquinamentoluminoso.it
> http://www.lightpollution.it/dmsp/
> http://www.istil.it
> ------------------------------------------------------------------
> -------------------------------------------------------------------------
> PIERANTONIO CINZANO
> International Dark-Sky Association - Italia
> Direttore Scientifico
> e-mail: cinzano@inquinamentoluminoso...
> web: http://www.inquinamentoluminoso.it
> ------------------------------------------------------------------------
>
> -----Messaggio originale-----
> Da: Yvan Dutil [mailto:yvan.dutil@sympatico...]
> Inviato: mercoledì 6 febbraio 2002 2.06
> A: DarkSky-list@yahoogroups...
> Oggetto: [DSLF] A few things we should know about light pollution!
>
> This a text I have prepare for the next dark-sky newsletter. Unfortunately,
> due to a lack of place,
> we will have to wait up to next edition to have it publish. Meanwhile, I
> will
> have probably publish
> my research paper in PASP. By the way, I am open to any comment.
>
> Yvan Dutil
>
> ----------------------------------------------------------------------------
> ----------
>
> Recently, two major legislations against light pollution have been rejected.
> One in the New York state, the other in the Czech Republic, One of the
> reasons invoked was lack of scientific justification for full cut-off lamp.
> Arguments invoked by astronomers (light above the horizon=pollution)
> backfired in face of analysis done by lighting engineers demonstrating that
> with less stringent optical cutoff, the poles can be more spaced for a same
> uniformity and the overall fraction of light that goes up, including the
> ground reflection, can be reduce by up to 20% (Remande 2000). Unfortunately,
> these two conflicting conclusions are based on simplistic model of the light
> pollution. Our understanding of the light pollution must improve otherwise
> the same scenario will repeat again.
>
> Common sense is that up-going light equals light pollution. The classical
> example is an old fashion lamp that emits directly 35% of the light up, 65%
> down of which 10% is reflected up. Overall, 45% of the light ends up
> illuminating the sky. Then with full cut-off optics, the direct emitted
> light
> goes down to 0%, and only the light reflected on the ground goes up, 10%. In
> consequence, we would expect a spectacular 88% in reduction of the overall
> pollution. Lighting engineer got even further, by following the engineering
> norms and applying their model for road illumination, they came down to the
> conclusion that light pollution can be minimized of you use semi-cutoff
> optics, which allows a few percents of light to spill above the horizon.
>
> Unfortunately, this model does not take account of a very simple fact: light
> emitted at low angle is more polluting that light emitted at the vertical.
> Simply, there is more air in the direction of the horizon than at the
> zenith,
> which provide more chance for a photon to get diffused. Don’t forget, that
> in
> essence light pollution is not a problem of light going up but a problem of
> light that was going up but got diffused on the ground. In consequence, it
> has been shown up by Pierantiono Cinzano & Francisco Javier Diaz Castro,
> that
> most of the light pollution is produce by light emitted at angle below 10
> degrees above the horizon. Unfortunately, the results of this key paper are
> presented in a form that renders them impractical for engineering practice.
>
> In order, to address this issue I have develop a simple model of atmospheric
> diffusion (Dutil 2002). It is essentially the same model as the one develop
> by Garstang and use recently by Cinzano et al. to produce their world atlas
> of light pollution. With some simplifications that ease the calculation but
> have little impact on the final result.
>
> For typical atmospheric condition, the light pollution efficiency peaks at 4
> degrees above the horizon at a value 5.85 times higher than at zenith.
> However order to evaluate the real impact of the light pollution, we have to
> sum the contribution of every angles. I have examined three typical emission
> functions: uniform over 10 first degrees above horizon (spilled light from a
> good lamp), lambertian (like a reflection on pavement) and uniform (like the
> emission of a globe). The pollution coefficients for each distribution are
> respectively 0.7950, 0.2902 and 0.4206. From these numbers we can deduce
> that a lumen of light spilled near the horizon pollution 2.74 more than the
> same lumen diffused on the asphalt, and 1.89 times more that if it was
> emitted by an infamous globe! Readers have to be advised that this result
> have not been peer reviewed yet and in consequence should be use with great
> care.
>
> What does this means in practice? If we used a standard albedo of 15% for
> the
> pavement, it can be shown that the reflected light will dominate the
> pollution budget if the light emitted directly above the horizon does not
> exceed 5.5%! Taken at face value this would means that lighting engineers
> are
> right and that simple cut-off optics would produce less light pollution
> since
> the only emit 2% of their light above horizon. If we recalculate the
> previous
> example with those number, we get: 35%+10%/2.74=38.65% vs 10%/2.74=3.65%. As
> we can see, the real reduction of light pollution is 90.6% instead of 88% as
> we have previously calculated.
>
> Is this the end of the full cut-off lamp? Nothing is less sure. First, we
> need to take account of the real amount of light spilled by lamp. Lamps are
> rarely exactly level and this inevitably increasing the light loss. This
> factor alone is enough to favor full cut-off optics. Second, the claims of
> engineers are based on a requirement of illumination uniformity. Real night
> vision is more complex and rigorous modeling with probably end up with a
> different result, especially if glare is taken into account.
>
> Do not forget that better lighting practice is our ultimate goal. Once the
> physics is well understood, optimization is easy.
>
> Reference:
>
> Cinzano, P., Diaz Castro, F. J., 2000, Mem. Soc. Astro. It., 71, 251
> Cinzano, P., Falchi, F., & Elvidge, C. D. 2001, Monthly Notices of the Royal
> Astronomical Society, 328, 689
> Dutil, Y., to be submitted to Publication of the Astronomical Society of the
> Pacific
> Garstang, R. H. 1986, Publication of the Astronomical Society of the
> Pacific,
> 98, 364
> Garstang, R. H. 1989, Publication of the Astronomical Society of the
> Pacific,
> 101, 306
> Garstang, R.H. 1991, Publication of the Astronomical Society of the Pacific,
> 103, 1109
> Remande, C., 2001, in Preserving the Astronomical Sky, IAU Symposium, Vol.
> 196, R. J. Cohen and W. T. Sullivan, III, eds.
>
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