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"The moon and the stars no longer come to the farm. The farmer has exchanged his birthright in them for the wattage of his all-night sun. His children will never know the blessed dark of night." (Leslie Peltier, from his autobiography, "Starlight Nights")

Preserving the Dark Skies, Our Precious Resource

General Information and Local Efforts

An effort to help promote awareness of our dark skies and the vagaries of light pollution has been initiated in January 2007. A collection of quality poetry and commentary for various outreach efforts. Nightsongs fuses art and science, compromising neither. The science is light but serious and the poetry is literary.

Light pollution
Wikipedia, the online encyclopedia

Preview to Encyclopedia Contents

1 Light pollution as a problem

2 Types of light pollution
2.1 Light trespass
2.2 Glare
2.3 Clutter
2.4 Sky glow

3 Consequences of light pollution
3.1 Energy waste
3.2 Reduced security
3.3 Loss of the night sky
3.4 Health problems
3.5 Disruption of the ecosystem

4 Reducing light pollution
4.1 Improving lighting fixtures
4.2 Adjusting types of lighting
4.3 Re-designing lighting plans

5 Organisations

6 See also Lighting

7 References

8 External links
8.1 Campaign groups
8.2 Research about light pollution
8.3 Collections of links related to light pollution
8.4 Miscellaneous

click this link for well written details

Unused Light, Overused Energy, Wasted Money

Information Sheet 110, August 1996
International Dark-Sky Association

International Dark-Sky Association
3225 N. First Ave., Tucson, AZ 85719 U.S.A.
E-mail: SaveOurSky@aol.com
WWW: http://www.darksky.org

Let's start this article about common-sense outdoor lighting with an "equation":

GLUT = Glare + Light Trespass + Uplight + Too Much Light

These are four negative factors often found with outdoor lighting. Not only does GLUT have a negative impact on our nighttime environment, the "nightscape" if you will, but it just doesn't make economic sense, either.

First, we'll take a brief look at each component of GLUT, and then we'll discuss some of the economic issues involved.

The 8th edition of the IESNA Lighting Handbook (1993) defines glare as the sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort or loss of visual performance and visibility. It stands to reason, then, that any good outdoor lighting design will minimize glare. If the light source itself is more apparent than what it is illuminating, then you have bad lighting.

Light trespass is light that is distributed where it is not wanted or needed. Streetlighting, for example, should light streets and sidewalks, not shine into second floor bedroom windows or illuminate rooftops. Also known as spill light, light trespass occurs whenever light shines beyond the intended target and onto adjacent properties.

Uplight is, in the truest sense of the word, wasted light. Light that goes directly up into the night sky is "lost in space" and serves no useful purpose. Uplight is the bane of astronomers and the occasional stargazer because atmospheric scattering artificially brightens the night sky, making distant celestial light sources difficult or impossible to see. Uplight often results from light fixtures which also produce glare and light trespass.

Too much light results when light levels exceed that needed for the task. Too much light often results from an unexamined "more is better" philosophy, or less innocent motives such as businesses trying to outshine their competitors.

Glare, light trespass, uplight, too much light; all of these things waste energy. And energy costs money. And the money involved is significant, because the operating cost of a light fixture throughout its lifetime is usually much greater than the initial cost of the fixture. Besides, even when energy is cheap, each kilowatt-hour wasted produces the same amount of unnecessary environmental pollution due to the production of that energy, regardless of its cost.

It is interesting to note that a great deal of attention has been paid in recent years to light source efficiency, but relatively little consideration has been given to the equally important subject of light fixture efficiency. Granted, many lighting manufacturers and lighting designers are enlightened about the virtues of using efficient light fixtures, but for some reason the message is simply not getting out to the majority of electrical contractors, lighting suppliers, builders, developers, architects, government officials, and homeowners.

It is also important to note that an inefficient light source used infrequently costs less to operate than an efficient light source operated dusk-to-dawn, 4100 hours per year. There are many situations where dusk to-dawn lighting is often not required: security lighting, task lighting, parking lot lighting, to name a few. Time controls, occupancy sensors, or manual switches should be used whenever possible, with an appropriate light source, of course.

The most energy efficient light source available is low pressure sodium, but it is often criticized because of its monochromatic nature. But mix in a little metal halide or fluorescent light, and color rendering is much improved. The potential exists to utilize multiple light source types to achieve greater energy efficiency and a lower life cycle cost than with traditional single-source designs.

Finally, let's take a look at spectral power distribution as another dimension of lighting economy. Is it really necessary for a "white" light source to pump out photons at nearly every wavelength from 380 to 780 nm, as metal halide does? Our eyes are basically tetrachromatic: maximum sensitivity for red-sensitive cones is at 570 nm, green-sensitive cones at 535 nm, rods at 505 nm, and blue-sensitive cones at 445 nm. Could not an efficient pseudo-white light source be constructed that would emit virtually all of its spectral power at these four, or another set of wavelengths? Astronomers would love that, because most of the visible spectrum would be unaffected by our outdoor lighting, and a small number of narrow spectral lines would be relatively easy to filter out.

To summarize: maximum utilization of light output where and when it is needed at IESNA recommended levels makes good economic sense and will minimize adverse environmental impacts. Avoiding outdoor lighting GLUT (glare, light trespass, uplight, and too much light) will take us a long way towards that end.

The International Dark-Sky Association, a tax-exempt non-profit membership based organization, has been founded to help overcome this awareness problem and to help preserve dark skies while at the same time maximizing the quality and efficiency of nighttime outdoor lighting.

This material is copyrighted (©) by the IDA, or others as noted. It may be reproduced for non-commercial usage provided that credit is given to IDA.

Photographic Collections

Photographic examples of lighting (Michigan)

Overview Articles on Effect of Light Pollution on the Biological Environment

Audubon Magazine

National Geographic News

-The night sky in the World Home Page
-How we surveil the situation of the night sky with satellites
-The DMSP satellite and its Operational Linescan System
-The World Atlas of sea level artificial night sky brightness (see pdf by Cinzano, P., Falchi, F., Elvidge C.D. 2001, The first world atlas of the artificial night sky brightness)
-Maps of the artificial night sky brightness
-Maps of the total night sky brightness
-Maps of the naked eye stellar visibility
-Maps of the number of visible stars
-Maps of the growth of light pollution
-Maps of the night sky in selected sites

The Night Sky, Italian Research

A Photographic Method for Measuring Sky Glow (1.2 MB PDF)

Sky Quality Meter

National Parks Dictum: Measuring Night-Sky Brightness (282 KB PDF)

Reference Material

IDA Resources for Learning

Outdoor Lighting Code Handbook, IDA 2002 (1 MB PDF)

The Institute of Lighting Engineers, UK

click on picture to access other tchnical materials

Determination of Limiting Visual Magnitude

The limiting visual magnitude is technically defined as the faintest magnitude that can be seen by the unaided eye at the zenith. This paramater is influenced by the transparancy or clarity of the atmosphere. This parameter is also influenced by the degree of light pollution present at an observing sight. The limiting visual magnitude is often used as an indicator of atmospheric transparancy and the general quality of the observing conditions at an observing site.

Discussion and Application of Limiting Visual magnitude

Limiting Visual Magnitude, Java Calculator

Determination of the Limiting Magnitude of a Telescope

This program by Bradley Schaefer calculates the limiting stellar magnitude an observer can expect to see with various types and sizes of telescopes, and under various conditions. It is fully discussed in SKY & TELESCOPE magazine, November, 1989, page 522.

Telescope's Limiting Magnitude

NASA Star Count Program