Dark Sky Lighting

by admin

Dark Sky Lighting
By Ashton Harr

For the past several decades, it has become increasingly more difficult to observe the night sky. Streetlights and atmospheric pollution have caused the night sky to be less dark and less clear. The beauties of the night sky can no longer be enjoyed from many cities. Too much and the wrong kind of lighting “blinds” the sky and thus you can see only the brightest stars. Fainter stars become invisible in light polluted areas.

Many of today s generation have not witnessed the beauty of the summer Milky Way or the mystical dance of the Aurora Borealis. The vast majority of this problem, known as light pollution, is caused by the proliferation of poorly designed lighting fixtures and/or installations.

The International Dark-Sky Association (IDA) was incorporated in 1988 as a tax-exempt non-profit organization operating exclusively for educational and scientific purposes. Their goal is to preserve and protect the nighttime environment and our heritage of dark skies through quality outdoor lighting.

A Prescriptive method provides the allowed lumens per square foot and minimum requirements for each LZ. Lighting Zones (LZs) correspond to geographical districts, typically based on population and/or use type. Each LZ (from 0 to 4) will provide a recommended upper limit on the amount of light. Astronomical observatories and open spaces with wildlife would be an LZ0, while commercial districts not in proximity to residential areas would be an LZ3. Certain special applications, such as prisons and large transportation facilities, would not be assigned an LZ category in the MLO but would require community and state or federal review for establishing lighting limits. A Performance method limits the lumens emitted by an optical system and is based on a new IESNA luminaire classification system. The system will allow manufacturers to describe their products in terms of the quantity of light emitted at various angles, using a rating system easily understood by those specifying and evaluating the suitability of a particular optical system.

Zenithal Limiting Magnitude Sky Features

4.5-5.0 Milky Way and Zodiacal light invisible. Typical conditions found in suburbs of major cities. Passing clouds are easily seen due to being lighted up from surrounding lights.
5.1-5.5 The indistinct Milky Way faintly visible only near the zenith. Zodiacal light invisible. M31, the Andromeda Galaxy, is barely discernible.

5.6-6.0 The Milky Way is now more easily seen, but lacks detail. M13, the Great Hercules globular star cluster can now be just glimpsed when near the zenith. The Zodiacal light is still invisible. The Milky Way from Auriga through Orion still invisible.

6.1-6.5 The Milky Way is now obvious and some detail can be glimpsed. The Zodiacal light is now barely visible, but not obvious. The Milky Way from Auriga through Orion is faintly visible. There is still noticeable skyglow along the horizon due to distant towns and cities.

6.6-7.0 Much structure is visible in the Milky Way. The Zodiacal light is an obvious cone of light. The major constellations are less obvious due to “noise” caused by the large number of faint stars now visible. Passing clouds appear as dark moving masses as they block the natural skyglow or the Milky Way. A few sources of skyglow are still visible.

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The Zodiacal light now encircles the entire ecliptic. There are no sources of skyglow along any part of the horizon. Many meteors are visible.

Ashton has a bachelor of science degree from UVA and a masters in business administration from the University of Richmond. Ashton was the V.P. of Operations for This End Up Furniture before opening the first Shades of Light retail store in Richmond, Virginia in 1986. She started Shades of Light national catalog operation in 1995 and launched the Shades of Light web site in 1997. Shades of Light specializes in the highest quality lighting, lamp shades, chandeliers, rugs, and curtains for every lifestyle. For more information please visit the Shades of Light web site and sign up for a free lighting catalog.

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