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[DSLF] Digest Number 1445
There are 4 messages in this issue.
Topics in this digest:
1. Re: Digest Number 1443
From: ctstarwchr@aol...
2. "blue" light - incandescent vs. fluorescent
From: glennlaser@aol...
3. Suffolk County, NY
From: Susan Harder <lookout@hamptons...>
4. Suffolk County, NY
From: Susan Harder <lookout@hamptons...>
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Message: 1
Date: Thu, 9 Sep 2004 12:01:28 EDT
From: ctstarwchr@aol...
Subject: Re: Digest Number 1443
In a message dated 9/9/2004 1:55:18 AM Eastern Daylight Time,
jackl@tetontel... writes:
>> It is predominantly the uniformity of the light distribution opposed
>> to the density of the light (footcandles or lux levels) on ground
>> surfaces that helps us to see better in a darkened outdoor environment.
>
> In a long time of reading this list, somehow I hadn't got this before.
Hi Jack:
Nice job on your web site. This may help explain uniformity and why
it is a vital element to achieve effective low impact lighting designs. It
does not mean lighting everything to absurd levels. When practicable,
we should try to spread minimal amounts of light evenly across the task
area using the least amount of fixtures with the lowest possible wattage
to meet the needs. More light than minimally needed for the task is not
better and merely wastes energy needlessly. Please realize not only
uniformity and light levels are important aspects of good design, and
plethora other important factors also come into play. Each application
is different and all come with unique sets of challenges. ;-)
Uniformity helps the eye maintain a stable state of visual adaptation.
This is vital for the outdoors because it improves visibility in areas not
receiving direct illumination. It helps to reduce bright spots that make
shadows appear darker than they really are. Well designed fixtures
applied in an appropriate manner spread most of their light outward at
angles below the horizontal rather than causing concentrated lumen
dumps in pools directly below. I have found using house-side shielding
with clusters of fixtures mounted on a single pole often helps minimize
the light pooling effect and improves uniformity when applying full cutoffs.
Fixtures with low vertical angles for the beam of maximum candlepower
tend to dump more of their emissions directly below opposed to sending
it outward, so to achieve good uniformity often requires more equipment
with closer spacing which raises light levels and increases operating and
installation costs. This (lack of) performance feature is often seen in many
decorative period style fixtures, but good engineering has improved them
somewhat in recent years. Most have short vertical distribution, however,
there are some good performers in the medium class offering full cutoff.
Your query is for a parking lot, but uniformity is a vital aspect of good
lighting design whether indoors or outdoors. In parking lots we do not
have walls, ceilings, furniture and other items to bounce the light off of
to indirectly spread its distribution. The outdoor environment is more
device specific where uniformity is achieved by direct emissions from
the fixtures in large open areas. A higher vertical angle for the beam of
maximum candlepower spreads the light over greater distances where
its pattern can be overlapped by light from adjacent fixtures, thus evening
the spread more effectively by improving uniformity. This aspect of fixture
performance also improves vertical illuminance at greater distances, and
it is not related in any way whatsoever to the IES cutoff classification.
For the best example of uniformity think of how good you can see when
walking in moonlight on a clear night without any manmade light present
in your field of view. The ground illuminance level during moonlit nights
rarely exceeds 0.01 to 0.02 footcandles, but the uniformity of that natural
light is 1:1 whether it is measured by max/min or avg/min methods.
Compare that experience to driving westward into the setting Sun when
it is close to the horizon. Uniformity of the scene *luminance* presented
to your eye goes off the scales due to high contrast caused by the Sun's
glare, but the general scene area will still be 1:1 on the ground. That
paradox brings the important element of contrast luminance into the
mix and is similar to what happens when floodlights illuminate parking
lots. It's fine for lighting a pile of lumber in a stock yard, but not for
where people are ambulating in the presence of moving vehicles on
slippery ground. ;-)
Our eyes are a comparative organ and the contrast between light and
dark and various hues of colors is what enables us to recognize objects.
Minimizing luminance contrast of manmade light *sources* nearly always
improves our visual perception when the scene is bright enough to see,
and tighter ratios for uniformity can sometimes allow much lower light
levels to be applied with no perceptible loss in visual perception.
Premcor Refinery Group realized this several years ago and now saves
nearly $500,000 annually after reducing wattage on their fixtures by 50%.
All they did to allow this wattage reduction was add shields with new
lamps and ballasts. This improved the uniformity by redirecting wasted
light and glare to the areas where it was needed and also helped the
company meet OSHA lighting standards for hazardous petrochemical
areas. It is the best industrial example of a lighting system improvement
that I know of and resulted in a new line of fully shielded industrial
fixtures
from Cooper Crouse-Hinds. An outstanding achievement Mr. Taylor!
The human eye has an astounding range of adaptability and we can see
outlines of ground features, read 3/8" print and recognize people's faces
several feet away when fully dark adapted merely by starlight during a new
moon which is an illuminance of only 0.0005 footcandles! The uniformity
of starlight from the Milky Way is also 1:1 as it is with the Sun during the
day because the source of light is located so far away and the angular
size for the cross-section of Earth is like a pinpoint from that distance.
Our eyes always adapt rapidly to the brightest objects in our field of view,
but take much longer to readapt to darker conditions. When uniformity
of a scene is tight (3:1 or less) and no glare or visible sources are present
the eye maintains a relatively stable state and does not need to adapt to
varying light levels beyond the luminance contrast of illuminated items in
the scene. Ideally this contrast of brightness should not exceed 10:1, but
we can tolerate up to 20:1 max to min illuminance for general tasks that
do not require seeing a great amount of fine details.
This is one reason why the uniformity recommendations are tighter for
more complex tasks like driving a car on a road or reading fine print in
an office opposed to driving much slower in a parking lot. As the need
to spot details increases, uniformity recommendations usually tighten
up with closer ratios.
One example is the Enhanced Security recommendations in RP-20-98
compared with recommendations for basic needs. Enhanced Security
requires slightly higher illuminance and tighter uniformity where minimum
maintained levels should be 0.5 horizontal (0.25 vertical) footcandles at
no less than 15:1 max/min uniformity, opposed to 0.2 horizontal (0.1 vertical)
footcandles at 20:1 max/min for basic needs in open parking lots. The
tighter uniformity helps the eye perform better and the higher illuminance
presumably helps people spot threatening situations that may be avoided
more rapidly, thus providing a higher degree of presumed safety. Of
course people must be paying attention to what they are doing because
light is not a magic force field that can protect us from crime and peril.
> I had been thinking about lighting for snowy areas. The local ski area
> is going for a LEED gold in a new design, they say. The old parking lot
> lighting was maybe four glary floods aimed at about 20 to 30 degrees
> from horizontal for maybe 7 rows of parking. I've sometimes thought
> that with snow on the ground, this may produce the least skyglow for
> the most vertical illuminance.
It sounds like a cheap but glary solution that could be sending direct
light 40 or more degrees above the horizontal depending on the vertical
beam spread of the fixtures. You made an interesting point about snow
reflections, however, direct emissions streaming skyward vastly exceed
what gets sent into the sky by ground reflections even from snow, but to
minimize the negative damage I would suggest meeting the minimum
requirements in RP-20-98 for basic needs using fully shielded fixtures.
It seems logical vertical illuminance may be enhanced to some degree
by reflections shining off of freshly fallen snow, but doubtful for grungy
snow that is packed and peppered with sand for enhanced traction.
To achieve the LEED point for light pollution they will be in good shape
if meeting minimum recommendations in RP-20-98. If a competent
designer does the lighting, they should be able to achieve basic needs
using four 30 foot high poles each fitted with three full cutoffs in a 120
degree radial array that offer medium vertical distribution in an IES
Type III or Type IV pattern, providing four single luminaires are placed
along the outer perimeter of the lot (total 16 fixtures). It can be done
using 250 watt HPS if it is a rectangular parking lot for 280 cars (7
rows of 40 stalls each). The lighting power density will be less than
0.05 watts per square foot and probably cost the same or less to run
as the current floodlight system. It sure will look a lot nicer to patrons
and anyone living within a 5 mile radius of the site on cloudy nights.
> Is there a general, quantitative, study of this?
There are many studies that have been published about these aspects
of design over the years but I cannot think of any specific ones to cite
at the moment. It has been a long day and I've not had any sleep since
Tuesday morning. This is merely knowledge I have learned from practical
experience over nearly two decades of professional design. You can
find a number of very good references in the Tech section of my LiteLynx
List online at:
http://members.aol.com/ctcadman/LiteLynx.htm#tech
More good stuff is available here:
http://www.cie-usnc.org/reports,%20abstracts_and_standards.htm
Hope the information helps and sorry for the lack of brevity! Anything
that travels at 186,000 miles per second is not easy to harness or explain
in simple terms, at least not for me. ;-)
Clear skies and good seeing,
Keep looking up!
Cliff Haas
Author Light Pollution Awareness Website (LiPAW)
http://members.aol.com/ctstarwchr
http://www.crlaction.org
Member: IESNA, CRL, NELPAG, AARP
[Non-text portions of this message have been removed]
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Message: 2
Date: Thu, 9 Sep 2004 21:37:40 EDT
From: glennlaser@aol...
Subject: "blue" light - incandescent vs. fluorescent
OK folks, I finally collected the data on the amount of "blue" in warm
fluorescent vs. incandescent. All of the information is from Osram Sylvania.
I think these is what it says, but I could use some help here from someone
with better math skills (Let's just say that I didn't' do so well in calculus
and it was a loooong time ago):
2700K fluorescent: 0.04 watts/1000 lumens in range 440-480 nm
Incandescent: 0.19 watts/1000 lumens in range 440-480 nm*
*Here is the question. The data for the fluorescent came as one value
in units watts/1000 lumens for various wavelength ranges, for example
440-480 nm.
The data for incandescent came as values in units watts/nm/1000 lumens,
for individual whole nanometers which means 20 values for the range
440-480. So, I added all those values and came up with 0.19, but I'm
not sure I can do that.
Second issue is the spiky nature of fluorescent. The 2700K fluorescent
has 0.04 watts/1000 lumens in the "blue", but 0.29 watts/1000 lumens
in the "violet" range 380-440 nm, much more than in blue! Do we know
RGC sensitivity for melatonin suppression in the "violet"??
If we had an RGC sensitivity curve across all wavelengths then it seems
that, using the lamp data, we could properly make recommendations about
what light sources are better as far as melatonin suppression is concerned.
I don't believe that Steve Pauley's statement in his recent paper that
"incandescent lights rather than fluorescent lights will reduce exposure
to blue color emissions" is proven.
I have all the data that I can send to someone, or post if Cliff tells
me how to do that.
Glenn Heinmiller, LC
In a message dated 8/19/2004 07:28:22 AM Eastern Daylight Time,
DarkSky-list@yahoogroups... writes:
Message: 5
Date: Wed, 18 Aug 2004 20:22:37 EDT
From: glennlaser@aol...
Subject: Re: RE: Article from Journal of Circadian Rhythms
Greg,
I assume by now from subsequent posts that we all understand now that
fluorescent sources are not necessarily "blue" or "cool" and in fact the
compact
fluorescent retrofit lamps being offered by utilities or sold in home
centers
for home use are typically 2700K, the same "warmth" as incandescent.
In commercial applications you will find 3000K, 3500K, and 4100K. Older
obsolete T12 installations are often the old "cool white" 4100K that kinda
gave
fluorescent a bad rap. Newer installations are more likely to be 3500K and
much
better color rendition than the old T12 stuff.
I'll try and find some information on the relative amounts of "blue" in
fluorescent and incandescent sources of the same color warm color
temperature.
.
Glenn Heinmiller, LC
[Non-text portions of this message have been removed]
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Message: 3
Date: Fri, 10 Sep 2004 10:34:38 -0400
From: Susan Harder <lookout@hamptons...>
Subject: Suffolk County, NY
For all of Suffolk County owned facilitates, parking lots, and roadways:
Signed this morning (a bi-partisan bill, unanimously approved 18-0 from
the Legislature)
http://www.co.suffolk.ny.us/legis/resos2004/i1574-04.htm
Susan Harder
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Message: 4
Date: Fri, 10 Sep 2004 10:35:29 -0400
From: Susan Harder <lookout@hamptons...>
Subject: Suffolk County, NY
TYPO, sorry:
For all of Suffolk County owned facilities, parking lots, and roadways:
Signed this morning (a bi-partisan bill, unanimously approved 18-0 from
the Legislature)
http://www.co.suffolk.ny.us/legis/resos2004/i1574-04.htm
Susan Harder
________________________________________________________________________
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