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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...>


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 
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:


More good stuff is available here:


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)


[Non-text portions of this message have been removed]


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


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  
fluorescent retrofit lamps being offered by utilities or  sold in home 
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 
fluorescent a bad rap.  Newer installations are more likely to be 3500K and 
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  
Glenn  Heinmiller, LC

[Non-text portions of this message have been removed]


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)


Susan Harder


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)


Susan Harder


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