Dobbins JLUS IMP Public Draft Light Pollution Study | Page 8
lunar illumination, and cloud‐coverage. The light reflectivity values published
by NOAA are expressed as radiance and calculated using a mathematical
formula to derive intensity values of watt per steradian per centimeter, i.e.,
10 ^‐9 W/cm*sr. For mapping and analysis purposes, the output radiance
values from the radiance calculation were categorized into ranges:
3,00‐6,00; 6,00‐20,0; 20,0‐40,0; >40,0 watt per stadium per centimeter.
Radiance as measured from ground sources is appropriate for this Study
since this indicates lighting levels experienced by pilots from an elevated
position in the sky as opposed to the light pollution that screens the night
sky when viewed from the ground.
After baseline radiance values were established, the Project Team analyzed
the results to conclude that the night sky conditions within the Light MCA
are poor. Light pollution surrounding Dobbins ARB occurs from various light
sources such as unshielded light fixtures and uncontrolled uplight. The
radiance values were mapped as contours and overlaid with Cobb County,
Marietta, and Smyrna existing land uses, future land uses, and zoning and
improvement districts to establish patterns, geographies, and land uses that
contribute the greatest to light pollution.
The Project Team evaluated zoning codes to determine if current policies
and regulations address the current and potential future lighting issues in
this area relative to their impacts on military nighttime training. Overall, the
current requirements contained in the county and cities’ development codes
support preventing light trespass onto adjacent properties, but does not
identify specific provisions relative to light controls that mitigate light
pollution to for the protection of military missions and preservation of
natural environments. The current regulations can be further enhanced to
ensure the overall light sources do not further degrade, creating an
environment where nighttime training at Dobbins ARB is rendered fully
ineffective. Ultimately, the loss of training capability could potentially result
in the realignment of some missions and the potential loss of associated
economic impact.
Page ES‐2
Findings
The overall findings indicated that the night sky in the Light MCA is poor,
with radiance values ranging from three (3) to greater than 40. Areas closer
to the installation, generally within three (3) miles, exhibit values greater
than 20, though high values are generally found along major highways and
thoroughfares and at major intersections where higher density development
has or is likely to occur. These areas correspond to a Bortle scale – a
method for ranking and describing sky brightness on a scale of one (1) to
nine (9) – of seven (7) (radiance values between 15.59 and 27), Bortle scale
of 8 (radiance values between 27 and 46.77) and Bortle scale of nine (9)
(radiance values greater than 46.77), indicative of a night sky significantly
impacted by light pollution. Night skies with a rating of seven (7) are typical
of suburban to urban transition described as a light grey with strong light
sources in all directions and brightly lit clouds. Night skies with a rating of 8
are typical of city skies described as the entire sky being grayish or brighter.
Night skies with a rating of nine (9) are typical of inner‐city skies described as
bright and discolored everywhere with stars weak and washed out.
Due to the regional redevelopment potential through community
improvement districts, master plans, and livable centers initiatives, the light
pollution in the Light MCA will not improve. The purpose of this Study and
the recommendations from this Study will assist Cobb County and the cities
of Marietta and Smyrna to prevent light pollution impacts from worsening.
Through the evaluation of the existing lighting regulations for Cobb County
and the cities of Marietta and Smyrna, it was found that although there is a
level of protection from increased light pollution through overlay districts,
there are enhancements that can be made to prevent the worsening of the
light pollution in the Light MCA. Such enhancements include: using and
installing backlight, uplight, glare (BUG) lights for all new nonresidential
construction instead of fully‐cutoff or fully‐shielded luminaires and not
permitting any light‐emitting diodes (LED) lights that exceed a correlated
color temperature (CCT) of 4100k. This CCT is a measurement of how white
DRAFT Dobbins Air Reserve Base Light Pollution Study
March 2018