[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[DSLF] Digest Number 564
_________________________________________________
To subscribe to the DarkSky List Forum send email
to: DarkSky-list-subscribe@yahoogroups...
Help save your town from obtrusive lighting --
invite your planning and zoning department to
join us! Ask them to visit the IDA website at
http://www.darksky.org today!
------------------------------------------------------------------------
There are 7 messages in this issue.
Topics in this digest:
1. Re: Rayleigh scattering & extinction coefficients
From: ctstarwchr@aol...
2. Re: FS fixtures are vital for reducing sky luminance
From: Jan Hollan <jhollan@amper....muni.cz>
3. DOT and FCO lighting
From: "ctstarwchr" <ctstarwchr@aol...>
4. non-FS and adaptation
From: Jan Hollan <jhollan@amper....muni.cz>
5. Re: DOT and FCO lighting
From: Paul Greenhalgh <fvas@shaw...>
6. Re: FS fixtures are vital for reducing sky luminance
From: Yvan Dutil <yvan.dutil@sympatico...>
7. Re: non-FS and adaptation
From: "ctstarwchr" <ctstarwchr@aol...>
________________________________________________________________________
________________________________________________________________________
Message: 1
Date: Sat, 26 Jan 2002 11:09:41 EST
From: ctstarwchr@aol...
Subject: Re: Rayleigh scattering & extinction coefficients
David:
A response returned to the question you asked about Rayleigh scattering a few
weeks ago and is included below. Answers to additional questions that I
asked about halos appearing around semi-cutoff in comparison to flat lens
(both FCO and Cutoff) fixtures are included as well.
Apologies for taking so long to get this information back to everyone.
Thanks to Chris for providing this detailed explanation. Hope it helps.
Cheers,
Cliff Haas
------------------ Forwarded Message --------------------
Cliff - I give some brief responses to Mr. Keith's questions below. Would
you please forward it to him or post it to the list, whichever or both
you think is most appropriate?
RE: Your observation that fully shielded luminaires do not produce the
typical "halo" you see around drop refractors. If I understand what
you are describing, I think this is simply a function of the flux
directed toward your eye (luminance integrated over solid angle of the
source) combined with the aerosol scattering in the intervening air.
Yes, this effect redirects flux originally directed downward into
every direction, including upward. But it is happening just as much,
per photon, to the light from fully shielded fixtures as to the light
from drop-refractor fixtures. Flat-lens luminaires do not show the
halo as easily just because their flux is very low at the high angles
you are observing. Try observing fixtures in fog, though.
Chris
> > Subj:Re: [DSLF] Raleigh Scattering and Extinction Coefficients
> > Date:12/14/01 6:43:07 PM Eastern Standard Time
> > From: david.keith@mindspring... (David Keith)
> > Reply-to: DarkSky-list@yahoogroups...
> > To: DarkSky-list@yahoogroups...
> >
> > My curiousity about some of the technical aspects of uplight/skyglow leads
> > me to some questions which I expect members of this group can confirm or
> > correct.
> >
> > My understanding of atmospheric scattering of light (i.e. radiation
between
> > 380nm and 7770nm) is that the dominant effect is related to Raleigh
> > (spelling?) scattering. This is the basis for why the sky is "blue" -
> > especially here in Colorado where we have less air/moisture. The "blue"
> > appears - as I understand it - because the probability of Raleigh
scattering
> > is very dependent on wavelength - shorter wavelengths are much more likely
> > to be redirected than longer ones. My brief web-search supports this,
> > including a statement that the scattering is proportional to the "inverse
> > fourth power" of the wavelength.
> >
> > Does this really mean that the probability of scattering is proportional
to
> > the wavelength of the light, in nanometers, raised to the -4 power?
Yes. The proper spelling is Rayleigh.
But other types of scattering are important, too, particularly low in
the atmosphere, where artificial lighting is used. When there are
particulates or aerosols in the air, these other types of scattering
become increasingly important, and can easily dominate over pure
Rayleigh scattering in common situations such as in big cities with air
pollution, where any dust has been stirred up by air movement (nearby
or even at great distance). These other types of scattering become
increasingly "grey" (that is, less strongly dependent on wavelength) as
particle size increases.
> >
> > My second "question" concerns "extinction coefficient", which I understand
> > is a technical term used in astronomy to describe the reduction in light
> > intensity during transmission in a direct line through the atmosphere. Is
> > this a correct description?
Yes. Extinction coefficients are a function of wavelength or
"passband."
> > Does it indeed evaluate the effects of both
> > flux scattering and flux absorption in total?
Typically, yes, unless specifically separated.
> > Is there a "typical"
> > proportion or ratio of light-absorption-to-light-scattering inherent or
> > understood for such a coefficient?
No. It varies depending on wavelength and aerosol content/size
distribution/composition. At good astronomical sites, where air is
very clear, there are indeed typical values for the extinction
coefficient(s), but city air near the ground is a different matter.
> >
> > Thanks for any and all responses - feel free to send directly to me
> > (keithd@resodance...) if this is no interest to the group.
> >
> > David Keith
> >
>
>
>
[Non-text portions of this message have been removed]
________________________________________________________________________
________________________________________________________________________
Message: 2
Date: Sat, 26 Jan 2002 18:00:47 +0100 (CET)
From: Jan Hollan <jhollan@amper....muni.cz>
Subject: Re: FS fixtures are vital for reducing sky luminance
> I must say that I am somewhat a little sorry to read that you had already
> written to paper that I am working on :( My calculations are also based on
> the formalism of Garstang but I minimize the burden of the computation
> by using a probalistic approach. Actually, my own program contain about
> 150 line of codes in mathlab!
>
> May I get a copy of your paper to see if I should continue to work on my
> own paper.
>
> Regards, Yvan Dutil
Dear Yvan,
I did not write any paper yet and won't soon. Just the programme available
at http://amper.ped.muni.cz/light/ies2 (with example results for some
manufacturers) and those two remarks on its results (the recent one and
the old one given as an URL). So, please continue writing, if you would
employ my programme, I'd be happy.
(I've noticed that apache on amper did not show the undispensable README
file in that directory, sorry, there is a symlink ``ReadMe'' now.)
The remarks missed an information that I've considered just single
scattering (unlike Cinzano et al.) -- adding a second scattering would
probably make the sky LP by direct light just above horizon even a bit
stronger. On the other side, statements on albedo and indicatrix type have
been misleading: albedo influence is simply a indirect proportionality (so
it _is_ important), indicatrix type is not very important (as I see now,
instead of relying on my memory). Diminishing zenith extinction makes the
sky LP proportion by non-FS luminaires a bit larger, namely for
non-changing CIE indicatrices (for the default one, the indicatrix has two
parts, the symmetric one from the gas always assumed to be responsible for
0.1 mag of zenith extinction).
> As for the BRDF, I got the CIE data. Unfortunately, they are almost
> useless for this peculiar application since the BRDF use by the lighting
> engineer are define only for grazing angle (<3 degres).
For obeying the road lighting standard it should suffice, as viewing
angles for CIE road-luminances-demands lie below 1.5 degrees (height of
the eye 1.5 m, 60 m from the first row of array points). IES demands
concern just viewing angle of 1 degree. (I take the values from the GE's
Aladan manual). The angles of incidence from the luminaires are to have
an almost full span (in the BRDF) to be useful, however.
Of course, real roads are no CIE standards and it would be _very_
interesting to know their BRDFs (new and worn, in wet conditions as well).
And *.ies of old luminaires. The ones I've seen had their acrylic bellys
not much transparent any more.
If you would send me those available BRDF's, I could perhaps implement
them in my programme, so that it would be able to pick up the most
suitable fixtures for a given purpose (from thousands of possibilities).
Next fortnight, maybe. And use them in Radiance (I'm slowly learning that
engine).
clear view with no glare,
jenik
________________________________________________________________________
________________________________________________________________________
Message: 3
Date: Sat, 26 Jan 2002 17:58:59 -0000
From: "ctstarwchr" <ctstarwchr@aol...>
Subject: DOT and FCO lighting
Greetings everyone:
A number of questions have surfaced recently about the various states
that use FCO roadway lighting. This IDA Information Sheet will help
to provide some examples to share with your legislators and/or state
Departments of Transportation.
http://www.darksky.org/ida/infoshts/is117.html
The survey concluded in 1997 and needs updating because significant
progress occurred in at least two New England states that I know of.
ConnDOT now only installs FCO for ALL replacement and new luminaires
in Connecticut. The ConnDOT official responsible for roadway
lighting admits the use of flat lens lighting greatly improves the
nighttime driving conditions after viewing several installations that
occurred over the past two years! ConnDOT was installing flat lens
cutoff luminaires (Lumark) on occasion after January of 2000 without
changing pole spacing or raising mounting height. They are learning
and doing a great job along the way.
ConnDOT stated on Thursday that pole spacing has decreased slightly
in the newly designed FCO lighting systems, but we have not yet
established by how much. It does NOT appear to be reduced by a
significant amount.
Other reports have come to me recently from several reliable sources
that Rhode Island DOT now uses FCO lighting on their highways, too.
In fact, further investigation indicates that RI-DOT now uses FCO
EXCLUSIVELY for ALL new and replacement luminaires on their primary
roads. RI-DOT is also considering dropping wattage for the new FCO
lighting systems from their past de facto standard of 400-watts to a
more eye friendly 250-watts! This is likely to improve nighttime
driving conditions significantly because the reduced glare and
pavement luminance will finally allow the eye (and our headlights) to
operate as originally intended.
Clear skies and good seeing,
Keep looking up!
Cliff Haas
Chair Light Pollution Education
Astronomical Society of Greater Hartford
http://members.aol.com/copernicanview
Light Pollution Awareness Website (LiPAW)
http://members.aol.com/ctstarwchr
________________________________________________________________________
________________________________________________________________________
Message: 4
Date: Sat, 26 Jan 2002 19:27:48 +0100 (CET)
From: Jan Hollan <jhollan@amper....muni.cz>
Subject: non-FS and adaptation
I suppose that one reason for the recommended (rather high) luminances and
uniformities is a simple fact:
Using glaring lights spoils the eye (mesopic) adaptation.
Why? Vertical illuminance of your face from distant luminaires is probably
a lot higher than from the road. You may demonstrate it by shielding a
white screen by a horizontal black cardboard -- over the cardboard, the
screen is illuminated just from the luminaires, below it, just from the
road.
To see most detail on the road, the eyes should be adapted to its
luminance. If they are forced by glaring luminaires to adapt to more light
(and not just vertical illumination is important, luminance maxima inside
luminaires play a role as well, diminishing eye pupils), less detail is
visible on the road (or generally in the illuminated landscape). It can be
compensated by more light, and very probably is, in contemporary
standards.
Animal vision is a fascinating tool, having no problem with twice lower
average luminances, as far as fully adapted to them. Glaring luminaires
prevent that (for the inevitable one above you, a visor (peak) on your
cap or at your car's screen is a sufficient protection).
Dark spots between glaring luminaires are really perceived darker than
(maybe intrinsically darker) those ones between less glaring ones. This is
the reason why uniformity is much less important with non-glaring
luminaires.
Am I true? Or, are there any standards accounting properly for adaptation
(of non-fixed view, as fixing it all the time to avoid glare is really
boring)? Are the contemporary roadway lighting standards really written
(non-explicitly) as worst-case ones?
(Of course I admit that all FS luminaires are not glare-free. Just the
low-glare ones proportion among them is surely higher.)
clear skies,
Jenik Hollan
PS.
your answer could help us to pass the LP law through Czech Senate next
week.
PPS.
Europeans, do you watch Moon-Jupiter encounter? Fascinating...
________________________________________________________________________
________________________________________________________________________
Message: 5
Date: Sat, 26 Jan 2002 12:46:44 -0800
From: Paul Greenhalgh <fvas@shaw...>
Subject: Re: DOT and FCO lighting
Cliff is there anything available that show's (from space) a before and
after shot of Washington State? Now that would be something to look at.
Thanks for that link by the way, definitely interesting and helpful in
future conversations with those in Governmental positions.
The only trepidation I have about FCO lighting is this "myth" that more
light is necessary, such as pole placements. Personally I think that there
is no need to add MORE lights to what is already in place. I think that more
lights being installed is an attempt to satisfy a false sense of proper
lighting or security. Am I way out in left field here or what? It seems to
me that initially once FCO lights are installed there is this rational that
what is not seen, (Glare, or fixed point of light, or observable light)
causes the rational to install more FCO lights to compensate. Where
compensation is not necessary, the same result is still there, but to the
observer there is this need to install more to satisfy the rational of
perceived common sense.
Such as you see in Washington state, where they have opted to put a light on
almost every pole. This to me seems to be excessive to my way of thinking,
and completely defeats the point of saving energy.
Your thoughts? Or for that matter anyone's thoughts?
Clear Skies!
_________________________________________
Paul Greenhalgh (Director)
Fraser Valley Astronomers Society
British Columbia Canada
http://www.fvas.net
________________________________
________________________________________________________________________
________________________________________________________________________
Message: 6
Date: Sat, 26 Jan 2002 18:00:31 -0500
From: Yvan Dutil <yvan.dutil@sympatico...>
Subject: Re: FS fixtures are vital for reducing sky luminance
Jan Hollan a écrit :
>
> The remarks missed an information that I've considered just single
> scattering (unlike Cinzano et al.) -- adding a second scattering would
> probably make the sky LP by direct light just above horizon even a bit
> stronger.
Yes, double scatering and higher order are significative when dealing
with the light pollution at various angle. Absorption by aerosol should
be also taken into account since they decrease the light pollution
efficiency near the horizontal.
> On the other side, statements on albedo and indicatrix type have
> been misleading: albedo influence is simply a indirect proportionality (so
> it _is_ important), indicatrix type is not very important (as I see now,
> instead of relying on my memory). Diminishing zenith extinction makes the
> sky LP proportion by non-FS luminaires a bit larger, namely for
> non-changing CIE indicatrices (for the default one, the indicatrix has two
> parts, the symmetric one from the gas always assumed to be responsible for
> 0.1 mag of zenith extinction).
You are right changing the model of the atmosphere do not change much
the overall shape of the function. I did calculation with a K parameter between
0 and 2 (clear to dirty) and this almost change nothing to the angular function.
>
>
> > As for the BRDF, I got the CIE data. Unfortunately, they are almost
> > useless for this peculiar application since the BRDF use by the lighting
> > engineer are define only for grazing angle (<3 degres).
>
> For obeying the road lighting standard it should suffice, as viewing
> angles for CIE road-luminances-demands lie below 1.5 degrees (height of
> the eye 1.5 m, 60 m from the first row of array points). IES demands
> concern just viewing angle of 1 degree. (I take the values from the GE's
> Aladan manual). The angles of incidence from the luminaires are to have
> an almost full span (in the BRDF) to be useful, however.
I agree, but we would like to input those in the model. Specular reflection
will inject more energy at low angle than a simple lambertian model. Since
light emitted at zero angle is much polluting this is a real issue.
> Of course, real roads are no CIE standards and it would be _very_
> interesting to know their BRDFs (new and worn, in wet conditions as well).
> And *.ies of old luminaires. The ones I've seen had their acrylic bellys
> not much transparent any more.
This is one of the avantage of the new luminaires. Many of those are scelled
and some are even auto-cleaning!
> If you would send me those available BRDF's, I could perhaps implement
> them in my programme, so that it would be able to pick up the most
> suitable fixtures for a given purpose (from thousands of possibilities).
> Next fortnight, maybe. And use them in Radiance (I'm slowly learning that
> engine).
As I said the BRDF use by the CIE are almost usless in there actual form for
light pollution studies. A real BRDF contain 4 parameters. The simplified
version used by the CIE reduc it to two parameters. Unfortunately, the two
parameters rejected are the most useful for light pollution purpose.
I will run code later today and send you the result. When I used the result
of the simulation of Baranne 2000, which does not take account of the
atmospheric dispersion in his model, it reduce the claim that the light
pollution produced by semi-cuttoff lamp is 20% below that of FCO
installation to about 10%. This is for an uniform illumination. To my
knowledge nobody ever attempted to do the same calculation with
the small target visibility method (by the way, the standard calculation
for this metric need to be revised).
I feel I will have to complete my paper very soon. I feel it is very much
needed. Be sure that I will at least quote you.
Regards,
Yvan Dutil
________________________________________________________________________
________________________________________________________________________
Message: 7
Date: Sat, 26 Jan 2002 19:36:43 -0000
From: "ctstarwchr" <ctstarwchr@aol...>
Subject: Re: non-FS and adaptation
--- In DarkSky-list@y....., Jan Hollan <jhollan@a.....> wrote:
>
> To see most detail on the road, the eyes should be adapted to its
> luminance. If they are forced by glaring luminaires to adapt to
> more light (and not just vertical illumination is important,
> luminance maxima inside luminaires play a role as well, diminishing
> eye pupils), less detail is visible on the road (or generally in
> the illuminated landscape).
Jenik:
This is probably the best descriptive reasoning that I have seen in
all of my research of vision and illuminating our environment. It
makes sense.
One sad thing about the measuring equipment commonly available is
that they only measure light in the photopic range. At the CIE
meeting held this past summer in Istanbul there was talk of needs to
develop a portable light meter that could measure accurately within
the scotopic and mesopic ranges which is very exciting news.
'Opic explanations simplified...
Scotopic -- all astronomers experience this when dark adapted. No
colors can be determined because only the rod photoreceptors in the
eye are triggered.
Mesopic -- anyone who has driven a car at night on a non illuminated
road has experienced mesopic vision. Colors are barely discernible
but don't try to match a pantone chart. The rod and cone
photoreceptors are engaged with mesopic vision.
Photopic -- anyone who has walked outdoors at high noon on a clear
day. The cone photoreceptors are highly stimulated and colors are
brilliant.
The study of vision is a fascinating subject and those seeking more
information will find a number of good references in the Health and
Tech Talk sections of my LiteLynx List.
http://membes.aol.com/ctstarwchr
If we are living by Robert's Rules of Order I make the Motion that a
new category be added to the list above:
Super-Photopic -- Anyone who has ever pumped gas into their vehicle
while under petroleum retail outlet canopies that are illuminated by
metal halide Scottsdale drop lens fixtures at night. Those retina
rippers are in a whole new class of their own!
Clear skies and good seeing,
Keep looking up!
Cliff Haas
http://membes.aol.com/ctstarwchr
________________________________________________________________________
________________________________________________________________________
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/