Dark Skies Bleg:

I am finishing a monograph on "dark skies" legislation, which restricts some night-time uses of electricity, in order to facilitate star-gazing. I would like to ask some questions to someone who is familiar with, and generally supportive of, such laws, and who also has some ideas for distinguishing reasonable dark skies regulations from unreasonable ones. If you would like, I can credit you in footnote 1 of the monograph. If you'd like to provide some guidance, please contact me via the e-mail link at the bottom of the left-hand frame on my website, Alternatively, if you have thoughts about the merits of particular dark skies regulations, feel free to leave them in the comments.

Gordon (mail):
I used to live in San Diego County, where the County attempted to enforce "dark skies" lighting ordinances to preserve the Mount Palomar observatory's ability to observe. Given the growth of San Diego County, and the ability of observatories to move to places like, say, the Atacama Desert in Chile, I don't think it worked.
10.4.2005 8:16pm
alkali (mail) (www):
I assume you are familiar with the International Dark-Sky Association (, which has a lot of learning on the topic.

There are some other rationales for limiting light pollution other than star-gazing:

1) Energy conservation. Globe-shaped light fixtures that are on all night and open to the sky are wasting energy, period, end of discussion. The good street light fixtures look like upside down shoeboxes; they use half the energy. Take a look at the streetlights next time you go for a drive; the new ones are usually the shoeboxes.

2) There are some pretty good reasons to think that illuminating the hell out of every square inch of urban areas actually encourages crime.

3) Friendliness to wildlife (birds, etc.) that can be confused by perpetual twilight.

4) General aesthetics unrelated to astronomical pursuits. (Darker skies look nicer.)
10.4.2005 8:31pm
alkalai, what's the rationale behind your point #2? Maybe I'm thick, but it seems counter-intuitive.
10.4.2005 8:47pm
alkali (mail) (www):
billb: The usual idea is that lighting deters criminals because they can be seen and reported to police. That is a good rationale for making sure that high traffic areas are well-lit, but in areas that are not likely to be observed by passers-by, lighting actually helps criminals perform crimes. For example, there is reasonably good data to suggest that turning off lights around school buildings at night deters vandalism, because the vandals can't see (and enjoy) what they are doing.

In addition, there is some reason to think that overuse of lighting is counterproductive. Suppose you have a parking lot that is partially comprised of a fenced off area in which high value items (e.g., new cars) are stored at night. One strategy is to illuminate the hell out of the entire lot. It might be more effective, however, to do the following: (1) light the entry/exit gates so that people with legitimate business can enter and leave safely; (2) don't light the area that's not fenced off, if there's no opportunity for crime there; and (3) put lights with motion detectors inside the fenced off area, both to provide light to persons with legitimate business and to alert passers-by to the presence of criminals.
10.4.2005 9:10pm
chris (mail):
As a purely hobby star-gazer, I'm in favor of reasonable dark sky laws for the same reason I'm in favor of noise ordinances. I want to be able to see the sky from my own property and my neighbors actions are infringing on this.
10.4.2005 9:13pm
Yeah, I wish I could do something about my neighbor's gazillion-watt light on their 2nd-story eaves that shine horizontally into my bedroom window. Maybe I should have posted this on the keep&bear thread. That's the more practical solution, eh? Or if not the more practical, at least the more satisfying. ;-)

I second the thought about lights and crime. Around here it's the meth dealers who light up their houses like supernovas. (And yes, my neighbor with the spotlight and the rottweiler probably is a drug dealer...)

cathy :-)
10.4.2005 9:35pm
Jim R. McBriarty (mail):
One reasonable standard for a 'dark skies' law might be objectively based: Could a star of such-and-such magnitude be seen by the naked eye?

One alternative put forth by some astronomers is the use of sodium halide lighting, which emits light closer to the yellow end of the spectrum, rather than the blue-white which is emitted by fluorescent fixtures. This type of light does not interfere with telescopic observation. In addition, the use of LED lighting might be considered. The wavelength of LED lights can be tuned to specific wavelengths, and they have the added bonus of using FAR less energy than either incandescent or fluorescent bulbs.
10.4.2005 9:57pm
That's nothing. I live next to Kenny Rogers' Roasters.
10.4.2005 10:06pm
Joseph Somsel (mail):
Here in San Jose, California, the street lights are sodium halide. The University of California's Lick Observatory overlooks us so we've tried to be good neighbors to the astronomers.

The reason sodium halide is used is because the emit highly monochromatic light that is easy for the astronomers to filter out without reducing the signal from the stars.

The downside is that the streelights are sometimes difficult to distingish from the yellow in traffic lights.
10.4.2005 10:15pm
rjh (mail):
Another common "dark skies" regulation is one that restricts the orientation of outdoor lighting. Lights that are directional and point down (at building, ground,etc.) are allowed and lights that point up are not. The goal of lighting buildings and grounds is still met, while substantially reducing the astronomical light glare. (This is because buildings, grounds, etc. reflect less than 10% of the light and the directional downward lights are usually less powerful because 100% of their light hits the intended target instead of beaming into the sky.)
10.4.2005 10:16pm
GMUSL 1L (mail):
1) Energy conservation. Globe-shaped light fixtures that are on all night and open to the sky are wasting energy, period, end of discussion. The good street light fixtures look like upside down shoeboxes; they use half the energy. Take a look at the streetlights next time you go for a drive; the new ones are usually the shoeboxes.

Um... Alkali, you might want to consult a physics or EE textbook. A lightbulb doesn't expend less energy if you put a box over it or otherwise direct the illumination downwards.

What I think you might have meant to say is that you're wasting lumens; If you put a mirrored cover above the light to redirect the upward illumination back downwards, then you can use fewer bulbs to get the same amount of light than you could without such a cover. It doesn't change the energy at all (not without actually removing or not turning on some lights), and the light redirection of non-mirrored or matte covers isn't going to do all that much.
10.4.2005 10:39pm
The major source of light pollution comes from misguided city lighting. I'd guess that the second major source is illuminated signs for closed businesses.

Dark-skies laws should keep clear of regulating private lighting and focus on State regulation of city and county lighting.

Personally, I have to say that street-lighting is usually a mistake in open areas. In dense city settings, the buildings are too tall and too close to the street to permit "naturally lighting" the area. But anyone who has driven in the country at night should be able to testify to the fact that lighting is only needed because headlights and periodic street light conspire to destroy one's night vision.
10.4.2005 11:33pm
alkali (mail) (www):
GMUSL 1L: Yes, the shoeboxes are mirrored on the inside.
10.4.2005 11:36pm
I live in Harpers Ferry, WV, which is surrounded by National Park Service facilities that are suppposed to follow specific guidelines to maintain "dark skies". The town has purchased and installed street lights that direct the light down to the steet, but some parts of the NPS campus were "designed" with those big globular lights that throw light everywhere, and there are other Na-vapor "security" lights that sprang up after 9/11.

Even though there is a well-defined policy guidelines that say they are not supposed to light things up like this, in a historic town, the perpertrators do not see fit to follow the guidelines, for aesthetic and "security" reasons. Fear trumps everything else. Writing laws to enforce dark skys will always have some sort of security or architectural exceptions, and people will use them to do whatever they want to do. I might suggest requiring motion detectors with short timers, and putting the burden-of-proof, at a very high level of proof(beyond a reasonable doubt?), on anyone who wants to deviate from this standard.
10.5.2005 10:07am
Clayton E. Cramer (mail) (www):
You've hit one of my hot buttons. From my blog:

Dark Skies

The Idaho Statesman published my piece about dark skies today:

One night, before the gray blanket rolled in over Boise, I drove up Idaho 55 toward Horseshoe Bend and turned left onto the summit road.

The Milky Way was breathtaking, and stars were as numerous as grains of sand on a beach. I've talked to Boiseans who can remember when the sky was almost that dark here. Wouldn't it be nice to have those dark skies again?

This doesn't have to be expensive — it can even save us money. A lot of businesses and individuals are wastefully lighting up the night sky; few traffic accidents or crimes take place 100 feet in the air.

Light fixtures that allow light to go out and up, instead of down, are wasting both electricity and money.

Compare a flashlight to a light bulb; the flashlight uses far less energy, because the beam is directed to a specific point. All this wasted energy is a crime against both the environment and a business' bottom line.

For streetlights, one alternative is a "full cutoff" light fixture that directs almost all light to the ground. I've talked to officials in both Boise and Eagle governments, and I am pleased to report that they are aware of this issue. New city streetlights are usually full cutoff fixtures — and I'm told that the older, wasteful streetlights in Boise (the "cobra head" design) will be upgraded as they wear out.

Streetlights aren't the only cause of this wasteful illumination of the night sky. Parking-lot lights, even full cutoff fixtures, create a problem when light bounces off the ground back into the sky.

I understand why many businesses (car dealerships, for example), like their properties brightly illuminated.

During night business hours, it makes the lot more inviting to customers; after hours, it may reduce theft and vandalism by making anyone on the lot clearly visible to passers-by.

Still, I find myself wondering if the after-hours lights have to be quite that bright.

It would certainly be a worthwhile experiment for a car dealer to reduce after-hours lighting for a few months — or perhaps use motion detector security lighting controls. Boise isn't Los Angeles; it is hard to imagine that reducing the lighting is going to dramatically increase vandalism and theft.

For new construction, the International Dark Sky Association has a Web page ( showing commercially available full cutoff fixtures.

A few dollars more per fixture now would more than pay for itself in reduced electricity costs over the lifespan of a commercial development. (A 250-watt light that is aimed down does a better job than a 400-watt light that goes everywhere.)

Even businesses that cannot afford to replace existing light fixtures should consider whether they can safely reduce outdoor illumination by reducing the wattage of existing bulbs, using motion-detector lighting controls, or using timers to shut down lights after hours.

Almost every business would like to find a way to increase profitability — and what better way than to save the environment and bring back the beauty of the night sky at the same time?

Clayton Cramer, of Boise, is a software engineer by day, amateur astronomer by night. His Web site is

Here is Ketchum, Idaho's dark sky ordinance. I've talked to the doctor who got it passed, as well as the Ada County ordinance on light pollution. He claims that there is some evidence for increased health problems associated with not having enough darkness at night.

Ada County's lighting ordinance doesn't have a direct URL, but this takes you to the index; see Title 8, Ch. 4, Art. H. Here's the meat:

A.Two Hundred Sixty Lumens Or More: Light fixtures that have a maximum output of two hundred sixty (260) lumens or more shall have an opaque top to prevent up lighting.
B.One Thousand Lumens Or More: Light fixtures that have a maximum output of one thousand (1,000) lumens or more per fixture shall have an opaque top to prevent up lighting and the bulb shall not be visible.
C.One Thousand Eight Hundred Lumens Or More: Light fixtures that have a maximum output of one thousand eight hundred (1,800) lumens or more shall have a "full cut off shield" as herein defined. See figure 4, section 8-1A-2 of this title.
D.Floodlight Fixtures: Floodlight fixtures shall be located in such a manner as to prevent direct glare into a roadway and to minimize impact on abutting properties.
1. Floodlight fixtures shall be set to only go on when triggered by activity on the property (sensor activated) and to go off within five (5) minutes after activation has ceased.
2. Floodlight fixtures shall be installed so that they do not tilt more than forty five degrees (45°) from vertical.
E.Up Lighting: Up lighting shall only be allowed in cases where the fixture and any light it emits are shielded from the sky by a roof overhang or similar structural shield.
F.Display And Security Lighting: Display lighting shall be turned off within thirty (30) minutes after close of business and shall remain off until sunrise or the opening of the business on the following day, whichever comes first. There are no time restrictions regarding security lighting.
G.Installed Height Of Fixture:
1. The height of a freestanding light fixture shall not exceed twenty five feet (25') or the height of the principal permitted structure, whichever is less. Light fixtures mounted on a wall may extend to the full height of the structure, but no farther.
2. The following standards shall apply to floodlight fixtures with a maximum output of nine hundred (900) lumens or more and other light fixtures that have a maximum output of one thousand eight hundred (1,800) lumens or more. Streetlights installed by the Ada County highway district or Idaho department of transportation shall be exempt from these standards.
a. Within a commercial or industrial base district, the effective zone of light (as documented by the photometric test report) shall not trespass on abutting residential properties. See figure 6, section 8-1A-2 of this title.
b. Within a rural or residential base district, the allowed height shall be determined by the setback from the property line as set forth in table 8-4H-1 of this section.

Height Setback From Height Setback From
Of Pole Property Line Of Pole Property Line
1 foot to 3 feet 0 feet 15 feet 36 feet
4 feet 3 feet 16 feet 39 feet
5 feet 6 feet 17 feet 42 feet
6 feet 9 feet 18 feet 45 feet
7 feet 12 feet 19 feet 48 feet
8 feet 15 feet 20 feet 51 feet
9 feet 18 feet 21 feet 54 feet
10 feet 21 feet 22 feet 57 feet
11 feet 24 feet 23 feet 60 feet
12 feet 27 feet 24 feet 63 feet
13 feet 30 feet 25 feet 66 feet
14 feet 33 feet
Note: Table is based on the formula H (height) = 3 + D (setback distance) / 3.
H.Underground Electrical Feeds: Electrical feeds to outdoor light fixtures shall be underground, not overhead.
I.Neon Illumination: Neon illumination shall be prohibited in the rural base districts.
J.Alternative Lighting Plan: The director may approve, or recommend approval of, an alternative lighting plan when the overall design, as proposed by the applicant, meets or exceeds the intent and the requirements of this article and shall not be detrimental to the public health, safety, and welfare. (Ord. 389, 6-14-2000)

My feeling is that as long as an ordinance limits lighting leaving your property, or entering your property, there's no problems about constitutionality. Clearly, if a neighbor's lighting is coming onto your property, it is a form of trespass. The problem of lighting that illuminates the whole sky seems a bit more problematic from a constutional standpoint, just because it is difficult to figure out exactly who is responsible for this. There's an analogy to Diamond v. General Motors, 20 CA3d 374 (1971), where the complexity of a class action lawsuit involving vast numbers of defendants killed the case (or at least gave the courts an excuse to do so).
I'm building a house about 20 minutes north of Boise right now because I have sixth magnitude skies--and I can make proper use of this 17.5" reflector of mine.
10.5.2005 1:04pm
shell (mail) (www):
Until February of this year, I worked for a company that sold commercial lighting. We often designed the lighting layouts for businesses or churches, and had to be aware of the ordinances required in various locations in the state of Virginia. The shoebox fixture is the standard most contractors will order to light up a road or parking lot. The shape of the reflector inside the shoebox housing determines whether the light will spread out uniformly in a circle around the pole (for the interior of a parking lot), project a pool of light in front of the pole (along the borders of a parking lot), or direct it along a path (sidewalk or road). The manufacturers are VERY aware of lumen efficiency. If they can light up the area with fewer fixtures than their competitor, they'll get the contract.

When it all works right, you don't notice it. When it's done wrong, you'll get splotches of inappropriate light or darkness. Even if the lighting design was done perfectly, it might have been installed wrong in the field. The reflectors all look like shiny mirrored bowls and it can be pretty easy to mix them up.

One of our manufacturers told us (as information to use during a sales pitch) that the biggest source of light pollution was auto headlamps. I don't know if that's true, but they are certainly a factor. Unfortunately, there's no way to provide a full cutoff headlight that still provides enough light to drive safely. (Although advances in road illumination--signage and pavement markings--will make it possible to drive with less light.)

(Finally, to cathyf: There may be some kind of nuisance ordinance on the books in your area that would cover the neighbor's light fixture. You should be able to require them to either remove the light or install a shield to keep it from entering your bedroom directly. Try contacting whatever agency is in charge of building inspections in your jurisdiction.)
10.5.2005 3:12pm
shell (mail) (www):
Veering a bit off topic, Virginia Tech University is doing some interesting research on highway lighting technology (along with testing other types of highway technology) with the Smart Road.
10.5.2005 3:17pm
Eh Nonymous (mail) (www):
Back to the question posed: Here's an extremely weak set of standards.

- if a regulation causes no rational lessening of community safety, it is not thereby more likely to be irrational
- if a regulation saves money and enhances public safety and enjoyment for the community at a minimal cost to a single regulated business, it is not thereby more likely to be irrational
- if removing a regulation would encourage wasteful lighting (spotlights aimed at the sky, for example, when not used for a public purpose) and not enhance public safety or enjoyment, removing the regulation might not be rational
- if a case can be made that the dark sky regulation advances no public purpose, but only burdens a private property owner in the full enjoyment of their property, then the regulation may be irrational and therefore unsupportable.
10.5.2005 5:05pm