Light Pollution

Dan Caton –President, North Carolina Section of the International Dark-Sky Association (NCIDA)

NC-APA Summer Planning Institute 8/1/01

Organizations

• International Dark –sky Association (IDA) www.darksky.org

• North Carolina Section www.ncdarksky.org

Objectives of This Presentation

• Show why astronomers are concerned and involved.

• Show what the problems are, with examples.

• Present some solutions to the problems.

• Ruin your view of the illuminated nightscape, forever!

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 in the country—the sky is darker!

A related problem: Glare

• Light directly seen from fixture is called “glare”

• Headlights are a familiar example.

• This … is glare

• Sadly, equated with good lighting!

The Global Problem

Light “Made in the USA”

Boone, 35 years ago…

… today

My Concern: our Dark Sky Observatory

Off the Blue Ridge Parkway, near Phillips Gap

•32-inch Telescope

•Lab for three astronomers and their students

•$500,000 investment

Dome and Cline Visitor Center

The Horsehead Nebula

M13 Globular Cluster

Research: Planetary Search

• Searching for planets in eclipsing binary star systems

• $100k National Science Foundation grant

• Another $150k in NASA grant funds

Where does the sky glow come from?

• Poor fixture design• Lack of shielding• Overlighting• Poor installation• Market Pressure

Fixtures: Good, Bad and Ugly

• Cut Off street lighting

• Full Cut Off parking lot lights

• Floodlights

Floodlights

• Almost horizontal

• No shielding• At night …

Floodlight used in ATMs

• Glare! Could you see a criminal? …

• He can see you…

Best: Full Cut Off (FCO) Fixtures

• “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…)

• Fixture shadow in daylight.

• Harder to maintain?

Roadway lighting-overhead glare

Sag Lens - Cobra heads• Filament below

reflector• Glaring to driver• Light polluting

Better, Full Cut Off 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 problems• Installed by amateurs

and utilities

The Glare at Night (From High, Too!)

Solution: Sky Cap

• GE prototype shown• Hubbell available• Full Cut Off• See results …

The Capped Light at Night

The Data

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% white to get color rendition

Decorative Street Lighting

• “Acorns” shown• Available with

“pie plate” internal reflector

• Consider a FCO like the GE Salem (demo)

• Not a major impact

Sidewalk Lighting

• Post-top fixtures like these here on campus are often very glaring…

• … there is more to lighting than just foot-candles!

Wall Packs

• One of the worst fixtures for pollution as well as glare

• Are available in FCO (see samples here)

• What is the point of these?

• Or 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

• IES RPA is 5 fc in dark environments, 10 in bright. This one ~60 fc.

•These are a danger – you are nightblind for several minutes after leaving and may leave headlights off.

•Danger to drivers passing by. These are actually horizontal billboards

• Bright metal halides with small diffusers make it worse than the average brightness suggests.

Compare to This

• This station ~ 35fc• Large diffusers

make bulbs easy on the eyes

An Almost Record …

• Blowing Rock required a lighting plan…

• Plan had peaks over 150 fc!

• Would not have even met existing 1-fc at property line

DOT Solutions• Specify FCO on roadways

so they are not lost in the bid process.

• Designate new highways as scenic to prevent billboards.

• Get legislation passed to forbid private lighting from interfering with driving.

Lighting Ordinances: Towns & Counties

Small towns and counties: simple ordinance can get 90% of the gain:

1. Downlighted signs

2. Caps on security lights

3. Limits on gas stations (< 40 fc max)

4. 0.5 to 1 fc trespass at property lines

5. Full cut off fixtures required on streets and lots

6. No floods (or must be shielded)

7. General limit (“in excess of need”)

Lighting Ordinances: Cities

• Cities: Careful, detailed approach probably necessary.

• An approach: make part of zoning, so they have to submit a lighting plan in order to get a conditional use permit. Enforcement and due process is often easer this way, too.

• IDA Code Handbook on the web at www.darksky.org (thorough but a bit much)

• Attend an ordinance-writing workshop (?)

• Hire a consultant.

Concluding…

• Like the background on this presentation, let’s make the orange glow of sodium vapor go away.

• Thank you for your time and attention.