Light Pollution: a Primer
The basic problem: Sky Glow
• Light from fixtures reflects off particles in the sky—”Sky Glow.”
• Large cities visible from tens of miles.
• The stars are not brighter here in the country—the sky is darker!
The Global Problem
Light “Made in the USA”
Boone,NC 35 years ago…
… today
The Horsehead Nebula
M13 Globular Cluster
Where does the sky glow come from?
• Poor fixture design• Lack of shielding• Over-lighting• Poor installation• Market pressure
Floodlights• Almost horizontal• No shielding• At night …
Better: Full Cut Off (FCO)
• “Shoebox” design• Why do you think
they are chosen? …
• Appearance in the daytime!
• At night …
Billboards: the Bad Way
• Uplighted• Most light reflected
into the sky• Often on all night
Better for the sky, but…
• Glare spot (illustrates the sky problem, though…)
Roadway lighting-overhead glare
Cobra heads• Filament below
reflector• Glaring to driver• Light polluting
Better, FCO Fixtures
• No light above horizon
• Non-glaring to drivers, too!
• May require more poles per mile
• At night …
“Security” Lighting
• “Dusk-to-dawn”• Security or
lighthouse?• Refractor very glaring
and light polluting• Frequent light trespass
and neighbor problem• Installed by amateurs
and utilities
The Glare at Night (From High, Too!)
Solution: Sky Cap
• GE SkyGard shown• Hubbell available• Total FCO• See results …
The Capped Light at Night
The Data
Private Security Lights
Car Sales Lots• Often grossly overlit• This one at 60-110
Fc on lot, 65 on road• Use astronomically
unfriendly metal halides
• Can use sodium with 10% while to get color rendition
Wall Packs
• One of the worst fixtures for pollution as well as glare
• Are available in FCO • What is the point of
these?
Sports Lighting
• Usually done poorly with lots of light pollution and light trespass.
• Can be done well as shown here, using fixtures like ….
… Musco fixtures
• Costs ~$100/fixture
Gas Station Canopies
Compare to This
• This station ~ 35fc• Large diffusers easy
on the eyes• Easy on the camera,
too…
How You Can Help
• Look at your own lights–are they needed? Could you have it capped? Put it on a switch, timer or a motion sensor. Put in a lower wattage bulb.
• Where do you eat out? Do the restaurants have glaring lights? If so, complain! …
• Are there some roadside lights that bother you as you try to drive? Complain!
• Is there a street light that shines into your window at night? Call up the utility and ask for them to put a sky cap on it. Don’t settle for simple spray painting of the fixture’s lens!
• Is there a street light that shines into your window at night? Call up the utility and ask for them to put a sky cap on it. Don’t settle for simple spray painting of the fixture’s lens!
• Spend some time at www.darksky.org and become (more of) an expert! Join the IDA.
• Write letters to your newspaper….
• Teach your friends about good and bad lighting–point it out when you are out with them at night.
• Make a difference! Start a project to get owners of “security” lights to have sky caps installed on them.
• Is there a street light that shines into your window at night? Call up the utility and ask for them to put a sky cap on it. Don’t settle for simple spray painting of the fixture’s lens!
• Spend some time at www.darksky.org and become (more of) an expert! Join the IDA.
• Realize that you are the ones with rights to speak for (“pursuit of Happiness” [Dec.Ind., par.2]).
• Develop a local ordinance….
Lighting Ordinances• A simple ordinance can get 90% of the
gain:• FCO, no floods (or or shielded floods)• Down-lighted signs• Caps on security lights• Limits on gas stations (< 35 fc max)• 0.5 to 1 fc trespass at property lines• General limit (“in excess of need”)• Coming: Model Lighting Ordinance (IDA
and Jim Benya, Benya Lighting Design)
Concluding…• Like the background on this presentation, let’s
make the orange glow of sodium vapor go away.