[Darksky][DSLF] Digest Number 413 (fwd)

Jan Hollan
Sat, 25 Aug 2001 19:27:37 +0200 (CEST)


So an interesting digest should not be missed...

---------- Forwarded message ----------
Date: 25 Aug 2001 09:02:43 -0000
From: DarkSky-listAyahoogroups...
To: DarkSky-listAyahoogroups...
Subject: [DSLF]  Digest Number 413

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There are 8 messages in this issue.

Topics in this digest:

      1. FCO vs SCO
           From: "Fabio Falchi" <fabio.falchiAlibero...>
      2. Re: Digest Number 412
           From: Susan Harder <lookoutAhamptons...>
      3. RE: Caltrans sign lighting updates
           From: "Fitzpatrick, Eric (J.)" <efitzpatAvisteon...>
      4. Re: FCO vs SCO
           From: ctstarwchrAaol...
      5. [pa-lights] [Fwd: I-99 lighting]
           From: "David Penasa" <dpenasaAbplw...>
      6. FW: [pa-lights] [Fwd: I-99 lighting]
           From: Arnold Kenneth J PSNS <arnoldkApsns....mil>
      7. Re:  [pa-lights] [Fwd: I-99 lighting]
           From: <cblAnofs....mil>
      8. Re: Caltrans sign lighting updates
           From: ctstarwchrAaol...


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Message: 1
   Date: Fri, 24 Aug 2001 16:13:11 +0200
   From: "Fabio Falchi" <fabio.falchiAlibero...>
Subject: FCO vs SCO

Dear friends,

we need to clarify the differences between full cut-off (FCO), cut-off (CO)
and semi cut-off (SCO).
CIE defines CO as a fixture with a maximum light
intensity of 10 cd/klm emitted at an angle 90 from the nadir and 30 cd/klm
at 80 from the nadir. Generally the maximum intensity is emitted at an
angle of 65.
The SCO has maximum light intensity of 50 cd/klm emitted at an angle
90 from the nadir and 100 cd/klm at 80 from the nadir. This fixtures have
generally the maximum intensity at an angle of about 75. The FCO has not
(as
far as I know) a CIE definition, but it is universally adopted that FCO
should have no emission above or at the horizon. This means a light
intensity of 0 cd/klm at 90 and above from the vertical. There are no
limitations whatsoever in the angles from 0 to 89.9999..., i.e where we
need it.
The fact that using a CO instead of a SCO needs more poles may be true
because, as seen, SCO spreads the light farther than the CO.
This is not true for the FCO because that has no limitations at 80. There
are FCO fixtures
with maximum intensity at angle of 70 and above.
The fact that SCO emits 100 cd/klm at 80 means that there is a important
glare factor to deal with. You may try this little experiment. Go in a
street lighted with the prismatic cobra head fixtures and cover with your
arm the row of lamps in order not to see them directly. Observe the street
for a while. Now lower your arm paying attention to what happen to the
perception of the street luminance. You'll see that the street seems to get
darker! The change is evident so that I'm confident that our eye will see
better in a FCO street than in a SCO lighted street with twice the
luminance. This
should be implemented in the standard rules used to design lighting.
A second think to stress is that the light emitted
directly from the fixtures is a lot more pollutant than the light diffused
by the street. A FCO fixture pollutes only via the reflected light by the
street (we may assume the indirect flux to be 10% of that emitted by the
fixtures). A SCO pollutes a 3% directly and a 10% of the remaining 97%
diffused by the street, i.e. 9.7%. It apparently seems that the SCO pollutes
only about
30% more than the FCO. This is not true. We need to study how the two
different fluxes (the direct one emitted at low angles above the horizon and
the diffused lambertian one emitted by the street) work to create light
pollution. Almost all of the direct 3% is diffused by the atmosphere, while
the indirect one contributes only by about 1/3 to create light pollution.
So, the 'polluting power' of a SCO is about 3/4 more than the one of a FCO.
There is a lot to spare, even if we should need a 10% more poles (and this
is not theoretically true for the FCO Vs the SCO, as seen above).
Clear skies,

Fabio Falchi

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FABIO FALCHI
Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso - ISTIL
Light Pollution Science and Technology Institute
e-mail:  falchiAlightpollution...
web:     http://www.lightpollution.it/dmsp/
            http://www.istil.it
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Message: 2
   Date: Fri, 24 Aug 2001 09:37:52 -0400
   From: Susan Harder <lookoutAhamptons...>
Subject: Re: Digest Number 412

RE:  Pole Spacing and semi and full cut offs

Dear all,

Regarding replacing semi cut off with full cut off.  I had a conversation with an engineer in Maine (their ord of ten years, requires full cut off replacements).  He told me that when you compare the photometrics of semi-cut offs that are 20 years old with the photometrics of new full cut offs, you do not need closer pole spacing
for the replacement.  When people compare the new semi cut offs with new full cuts offs, at that point you may need closer pole spacing.

Hope that helps someone.

Susan Harder





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Message: 3
   Date: Fri, 24 Aug 2001 16:20:00 -0400
   From: "Fitzpatrick, Eric (J.)" <efitzpatAvisteon...>
Subject: RE: Caltrans sign lighting updates

This subject still gets me riled up.  Why even bother re lighting the signs?
Again, we don't light signs here in Michigan and the signs have excellent
night time visibility.  Not to mention Michigan has  more challenging
weather which has potential to reduce visibility.  Instead of relamping the
signs, why not use those funds to ensure the signs have good night time
visibility without lighting them.  Eventually, California will come out
ahead in electricity savings, not to mention saving energy.  Isn't
California suppose to be having energy availability issues?  It sure doesn't
seem that way with this type of wastefull action. 

OK, I'm through venting.


   Date: Thu, 23 Aug 2001 16:37:58 -0700
   From: Dave DeSantis <desantisAsasquatch...>
Subject: Caltrans sign lighting updates

To all folks:

Caltrans is now starting to use the Philips QL induction system to light
their
highway signs.


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Message: 4
   Date: Fri, 24 Aug 2001 15:40:54 EDT
   From: ctstarwchrAaol...
Subject: Re: FCO vs SCO

In a message dated 8/24/01 10:27:23 AM Eastern Daylight Time, 
fabio.falchiAlibero... writes:

> CIE defines CO as a fixture with a maximum light intensity of 10 cd/klm 
> emitted at an angle 90 from the nadir and 30 cd/klm at 80 from the nadir. 
> Generally the maximum intensity is emitted at an angle of 65.

Hi Fabio:

Thank you for presenting that excellent information.  It is interesting to 
note the differences between the CIE and IES definitions for Cutoff, 
Semi-cutoff, and Full Cutoff luminaires.  Perhaps this information might be 
easier for people to digest if the values are translated into percentages of 
luminance rather than with the raw numbers themselves.

                          CIE               IES
Full Cutoff Luminaire
Above horizontal       not defined           0.0%
Above 80 degrees       not defined          10.0%

Cutoff Luminaire
Above horizontal           1%                2.5%
Above 80 degrees           3%               10.0%

Semi-Cutoff Luminaire
Above horizontal           5%                 5%
Above 80 degrees          10%                20%

Noting this, it is no wonder why many might people find these terms confusing 
since there is no universal engineering convention that has been agreed upon.  It would seem the European standard is more favorable toward light pollution reduction, whereas the IES standard may be more favorable to wider pole spacing.

Most roadway luminaires are available in various different photometric patterns with short, medium, and long spacing attributes.  Per the IES "Lighting Handbook HB-99" the following spacing intervals are recommended.  This of course should be checked with the luminaire manufacturer as well, but for general guidelines the following is given:

Distribution Type       Spacing Interval between luminaires

Short distribution      4.5  Mounting Height (MH)
Medium Distribution     4.5  MH to 7.5  MH
Long Distribution       7.5  MH to 12.0  MH

Theoretically, one can safely space luminaires up to 360 feet apart using a 30 foot mounting height.  For a residential setting located in Texas, I have run evaluation models that mounted 100-watt HPS lamps in GE M250A2 FCO (long distribution IES type II) cobraheads spaced at 200 foot intervals using a 30 foot mounting height that resulted with 0.4 FC average maintained illuminance that had a 3.9:1 uniformity ratio!  IES specs require 0.3 FC A 6:1 uniformity for this application, which is only 65% as good as the model above delivered.  It CAN be done without decreasing pole spacing, given the proper conditions (mounting height vs. distribution type vs. lumen package) are met.  A system like this costs ~==$917 per year in energy operating costs per mile of continuously lit road if run on a metered system with the utility company charging $0.063/kWh.  If anyone would like to see a screen snapshot of this evaluation model showing isofootcandle illuminance please contact me privately.

> You may try this little experiment. Go in a street lighted with the 
> prismatic cobra head fixtures and cover with your arm the row of lamps in 
> order not to see them directly. Observe the street for a while. Now lower 
> your arm paying attention to what happen to the perception of the street 
> luminance. You'll see that the street seems to get darker! The change is 
> evident so that I'm confident that our eye will see better in a FCO street 
> than in a SCO lighted street with twice the luminance. This should be 
> implemented in the standard rules used to design lighting.

This is an excellent demonstration that I have used with people for a couple of years now.  The reaction is very dramatic with high incidents of visible glare. I also use the same example when speaking with municipal officials indoors if there are any visible light sources in the room.  It is funny because most people tend to look directly at their hand shielding the light rather than at the contents of the room.  Be aware of where your subjects are looking if you use this very powerful demonstration.  It sells the benefits of FCO lighting every time.

With low angle glare removed from the equation there is no logical need that I can see for such high illuminance levels shown in IES and AASHTO standards.  I have noticed that uniformity ratios often tend to improve when the gross 
illuminance levels are lowered, within reason of course.  It is not the 
quantity of light that enhances visual acuity, but rather, it is the 
uniformity ratio (average illuminance divided by the lowest illuminance level 
of a sampled area) that enhances our visual performance at night.  Prime 
example is the full moon A 0.01 footcandles with a uniformity ratio of 1:1.

> A FCO fixture pollutes only via the reflected light by the street (we may 
> assume the indirect flux to be 10% of that emitted by the fixtures). A SCO 
> pollutes a 3% directly and a 10% of the remaining 97% diffused by the 
> street, i.e. 9.7%. It apparently seems that the SCO pollutes only about 30% 
> more than the FCO. This is not true. We need to study how the two different 
> fluxes (the direct one emitted at low angles above the horizon and the 
> diffused lambertian one emitted by the street) work to create light 
> pollution. Almost all of the direct 3% is diffused by the atmosphere, while 
> the indirect one contributes only by about 1/3 to create light pollution.  
> So, the 'polluting power' of a SCO is about 3/4 more than the one of a FCO. 
>  There is a lot to spare, even if we should need a 10% more poles (and this
> is not theoretically true for the FCO Vs the SCO, as seen above).
> 
Any luminaire that blasts glare at low angles will reduce visual performance 
and thereby affect safety of drivers and pedestrians.  The same is true for 
security lighting.  Showing the cops (or business owners) how one can 
literally disappear under the veiling luminance of a bright floodlight is 
loads of fun!  Ask then whether the glaring light is providing a value or 
providing a hindrance to safety and security.  The answer is pretty obvious 
and most people will get it right away.  Try it in your area sometime (even 
with uninvolved strangers who have nothing to do with the lighting) and let 
us know what the reactions were.  Dark clothes are recommended.

Clear skies,
Cliff Haas
     ________
 ||==|________|
 ||  /  FCO  \
 || / the way \
 ||/  to go!   \
 |/    www.     \
 /| darksky.org  \
/||_______________\_ 

Light Pollution Awareness Website
http://members.aol.com/ctstarwchr


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




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Message: 5
   Date: Fri, 24 Aug 2001 16:38:56 -0600
   From: "David Penasa" <dpenasaAbplw...>
Subject: [pa-lights] [Fwd: I-99 lighting]

> We need to have the manufacturers develop full cutoff luminaires for
roadway
> lighting that can meet the uniformity requirements and match the
semi-cutoffs in
> pole spacing.

Not possible, due to laws of physics!

>We also need to have the uniformity requirements evaluated to
> allow for glare reduction with full cutoffs.

This seems possible, with research!

David






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Message: 6
   Date: Fri, 24 Aug 2001 16:06:26 -0700
   From: Arnold Kenneth J PSNS <arnoldkApsns....mil>
Subject: FW: [pa-lights] [Fwd: I-99 lighting]

> We need to have the manufacturers develop full cutoff luminaires for
roadway
> lighting that can meet the uniformity requirements and match the
> pole spacing.

???????????????????????????????????
Not possible, due to laws of physics!
???????????????????????????????????

I  DON'T UNDERSTAND THIS STATEMENT,  UNLESS UNIFORMITY REQUIREMENTS ARE
MEASURING LIGHT ABOVE HORIZONTAL,  OR MAYBE  I HAVE A MISCONCEPTION ABOUT
FULL-CUTOFF.  COULD YOU EXPOUND  ON THIS A LITTLE BIT?

Thanks,  Ken



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Message: 7
   Date: Fri, 24 Aug 2001 16:17:18 -0700
   From: <cblAnofs....mil>
Subject: Re:  [pa-lights] [Fwd: I-99 lighting]


New RPs in IESNA based on STV (Small-Target-Visibility) have been shown to 
yield pole spacings with FCO that are greater than or equal to SCO
or other optics types.  I am no great fan of STV - the understanding of
the visibility of these small targets to the needs of the driving task
are too weak - but the approach is a clear improvement on illuminance 
specs combined with uniformity ratios.

But it is clear that the STV approach verifies the idea that
lower-glare installations indeed DO lead to lower uniformities and
even lower average illuminances.

The pole spacing concerns relative to FCO and other optics types are
an artifact of illuminance-driven designs, which has become an
outdated approach.  When visibility criteria
are used instead, even as poorly as they are presently understood,
pole spacing and therefore lumens/mile or watts/mile are generally
better with FCO.

Unfortunately, illuminance/uniformity design is still the most commonly
used.  Despite movement toward better lighting based on better
understanding of the lighting tasks underway at IESNA, AASHTO has yet
to exhibit any movement.  Since most highway departments follow
AASHTO, there you have it.

This issue has been discussed by Jim Havard (IESNA Roadway Lighting
Committee) in several recent presentations at IDA and IESNA meetings.

Chris

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 Christian B. Luginbuhl                            Phone: 520-779-5132
 U.S. Naval Observatory Flagstaff Station            FAX: 520-774-3626
 Flagstaff Arizona 86002-1149 USA                  Email: cblAnofs....mil
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Message: 8
   Date: Sat, 25 Aug 2001 02:26:25 -0000
   From: ctstarwchrAaol...
Subject: Re: Caltrans sign lighting updates

--- In DarkSky-listAy....., "Fitzpatrick, Eric (J.)" <efitzpatAv.....> 
wrote:
> Why even bother re lighting the signs?
> 

A very good point Eric.  I am pleased to see the QL series lamps 
being used not only for their longevity (25 years), but also for 
their lower lumen package.  Presently they give ~=70 lumens per watt 
and have a very slow lumen depreciation profile.  You do make a very 
good point about the waste of energy though.  Reflective paint would 
offer good sign visibility for free like it does in many states 
already, CT being one of them.

To my knowledge, KIM Lighting is the only manufacturer that has 
introduced a new QL series FCO area light.  As I recall, it is 
available in 85 or 160 watt versions.  More benefits of induction 
lighting are its instant on/instant restrike capability, which makes 
it ideal to use for true security lighting that is controlled by 
proximity sensors rather than just staying on all of the time.  I 
have seen it coupled with FCO fixtures at a high school in Granby, 
CT.  The lighting stays off until someone walks or drives near the 
pole.  When on, it appears to be very close in color to most HPS 
lamps but its CRI/CCT is a bit better.

Clear skies and good seeing,
Keep looking up!

Cliff Haas




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