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  1. #1
    Tony Flanders's Avatar
    Tony Flanders Guest

    Default Sources of Light Pollution

    Has anybody done a scientific study of the sources of light
    pollution in a typical American city? It sounds like something
    that would be fairly easy to derive from satellite photos or
    reconaissance aircraft.

    One tends to think of street lighting as the primary culprit
    because it is ubiquitous, but I have my doubts. For one thing,
    even the worst street lighting is fairly well shielded, as these
    things go. I bet a conventional "bad" cobra light doesn't send
    more than 20% of its light upward. The new fashionable acorn
    lights are much worse, but even they are pretty well shielded
    on top.

    Recently, attempting to measure sky brightness at various spots
    around town, it has dawned on me that ball fields are a truly
    major source of light pollution. In Boston, Fenway Park is an
    obvious culprit, but the Boston University field is every bit
    as bright as Fenway, and is illuminated much more of the time.
    It has a large, measurable effect on sky brightness within a
    radius of one or two miles. Then there are Harvard's fields
    and MIT's fields and the various municipal fields, which remain
    illuminated increasingly many nights and increasingly long into
    the night. I have measured nearly a 50% drop in sky brightness
    between 9PM and 5AM, and I bet that a good chunk of that is due
    to ball fields.

    Other sources I can think of:

    3. Automobile headlights
    4. Parking-lot lights (municipal, industrial, commercial)
    5. Industrial/commercial security lights (hard to separate from #4)
    6. Residential security lights
    7. Car dealers
    8. Prisons

    Anything else? Note that of these, ball fields, car dealers, and
    prisons are particularly threatening, since they aim (for perfectly
    valid reasons) to make outdoor areas as bright as day. By and large,
    they use fairly well shielded lights to achieve that aim, ball fields
    being probably the worst exceptions, but even a small patch of day
    emits a mighty lot of light towards the sky.

    - Tony Flanders

  2. #2
    Davoud's Avatar
    Davoud Guest

    Default Sources of Light Pollution

    Tony Flanders:

    All of the above. And illuminated signage is big. And porch lights are
    small. In my opinion, it's cumulative -- collect enough drops of water,
    and you've got an ocean.

    I'm not generally a pessimist, but I don't think that there is much
    hope for slowing, much less reversing, the spread of light pollution.
    In spite of local successes by IDA <>, the
    public are largely unaware that light pollution exists. Politicians
    have more important things on their minds, and even if they wanted to
    reverse the trend by legislation, they would face insurmountable
    opposition from the business community.

    There may be a lesson in the recent passage of the Do-Not-Call bill;
    the politicians did surmount opposition from the business community
    because 50 million Americans had signed on to the list. So, if you can
    get 50 million people to say "We want dark skies" you might be able to
    do something.


    usenet *at* davidillig dawt com

  3. #3
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Sources of Light Pollution

    >I'm not generally a pessimist, but I don't think that there is much

    I think there is hope, but not because the public interest will demand it but
    rather because as energy costs rise, efficient use of lighting will become a

    It may not happen tomorrow but it will happen IMHO.


  4. #4
    Roger Hamlett's Avatar
    Roger Hamlett Guest

    Default Sources of Light Pollution

    "Tony Flanders" <> wrote in message ...
    Remember that if the albedo of the road is not very low, a lot of the light
    that is sent downwards, ends up bouncing back upwards. It is really
    noticeable, that street lighting gives far worse light pollution, when the
    road surfaces are concrete, than when dealing with tarmac surfaces.

    In the UK, the ones that really 'scream' at you, are golf driving ranges.
    They tend to be lit from the driving point, or close to this end, with large
    amounts of lighting aimed 'along' the range. A friend was commenting on this
    just the other day, with the visible 'dome' of pollution from a range over
    four miles away...

    Best Wishes

  5. #5
    Jim Miller's Avatar
    Jim Miller Guest

    Default Sources of Light Pollution

    agreed on the energy savings driver... hopefully the long island story will
    reproduce itself successfully across the country. certainly wouldn't hurt to
    reduce our energy imports as well.

    a nearby golf range which is lit at night is a huge source of light
    pollution near me. from the highway 5 miles away it looks like someone is
    filming the mothership scene of close encounters.


    "Jon Isaacs" <> wrote in message

    I think there is hope, but not because the public interest will demand it
    rather because as energy costs rise, efficient use of lighting will become a

    It may not happen tomorrow but it will happen IMHO.


  6. #6
    Scott Smith's Avatar
    Scott Smith Guest

    Default Sources of Light Pollution

    I live in a small town North of Nashville, TN and when I first moved here
    eleven years ago the skies were very dark due to being appx 25 miles away
    from the city and mall lights. About three years ago the mayor and council
    of my small community placed approximately fifty street lights at various
    locations inside the 4 mile by 8 mile city boundaries for security reasons,
    even though we had zero crime. Even with low wattage low-pressure sodium
    (yellow) lighting, the sky is considerably more light polluted especially on
    nights with higher humidity. I must say that personally, the street lights
    were my largest source of pollution. I approached our power coop without
    discussing with the mayor or council and they agreed to spray the inside of
    the glass shades black around my home. The lineman said that they would
    rather do this than replace lights that were shot out by BB guns....I
    remained silent. This solution allowed the light to illuminate the streets,
    to keep my light dependent neighbors happy, while cutting down the unwelcome
    dispersion into the surrounding sky. I gained "some" of my dark sky back.

    Scott Smith

    "Tony Flanders" <> wrote in message ...

  7. #7
    Davoud's Avatar
    Davoud Guest

    Default Sources of Light Pollution


    Jon Isaacs:

    I would like to think that you are right -- but GM continues to meet
    the demand for larger and more socially irresponsible so-called SUV's,
    and I think that it is evident that the American people are willing to
    accept terrorism and war as part of the cost of having energy to burn,
    be it in SUV's or inefficient lighting.


    usenet *at* davidillig dawt com

  8. #8
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Sources of Light Pollution

    >a nearby golf range which is lit at night is a huge source of light

    Here is San Diego there is actually a signficant aware of how light pollution
    affects the night sky. This is because of the closeness of Palomar Mountain
    and efforts to reduce the encroachment of the cities lights.

    The city council considers the effect of light pollution when making street
    lighting decisions.

    And too, both of San Diego's professional teams, the Chargers and the Padres do
    their part to keep light pollution at a minimum by making sure they alway miss
    the playoffs. <g>


  9. #9
    JBortle's Avatar
    JBortle Guest

    Default Sources of Light Pollution

    Davoud posts:

    As someone who has watched the spread of light pollution for some 50 years now,
    I'd have to say, sadly, that nothing imaginable is going to stop it nor slow it
    to any degree. Unless one outlaws urban sprawl, which will never happen, one
    can only envision a not too distant future where most observers (at least those
    east of the Mississippi) will have to travel hours just to reach magnitude 5.0
    skies. The IDA can encourage all the shielding it may care to but this will, at
    best, only slow the growth of light pollution and never, ever reverse it -
    except perhaps in the areas of cities where the situation is already an
    observing disaster.

    In the NYC area 50 years ago one could see the milky way extend horizon to
    horizon just 20-25 miles outside the city. This vanished by about 1965. Some 35
    years ago conditions at my rural home 75 miles from NYC were comparable to
    those on Mt. Palomar at the very same time (I had a chance to compared the
    sites) and the NYC/metropolitan area light glow was little more than a hint on
    the southern horizon. Today my site is fully alight and the local population
    growing rapidly. I have a limiting magnitude of 5.5 (in 1970 it was 7.5) and
    I've noted that the NYC-metro glow can be clearly seen out to at least 150

    This has all been the result of growth/population expansion - urban sprawl. As
    long as this continues, light pollution will expand expotentially and only the
    very naive and the dreamers will see hope of curtailing the situation. I'd love
    to suggest otherwise, but these are the hard, cold facts of reality.


  10. #10
    donutbandit's Avatar
    donutbandit Guest

    Default Sources of Light Pollution

    I don't think you can rule out any source of light, even downward directed
    streetlights, as a portion of the light is reflected upward.

    What's the first thing someone does when they move into the country? They
    put up a halogen light.


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