Dobbins JLUS IMP Public Draft Light Pollution Study | Page 123

T echnical Basis and Background
The purpose of the POLC is to establish a balance between outdoor lighting needs of
commercial, industrial and residential lighting users and the need to limit unintended or
obtrusive effects of outdoor lighting use such as light trespass, glare, excessive energy use, and
sky glow. Poorly shielded lighting that shines directly from high intensity light fixtures into
people's eyes, causing glare, always decreases visibility. Lighting levels above those needed for
safety, utility and security consume more energy than needed, and produce more sky glow.
Sky glow interferes not only with astronomical research in the state of Arizona, but also affects
the environment and quality of life for all residents in the state. Reasonable amounts of lighting
mean reasonable amounts of energy use, lower energy bills, and a more sustainable
environment. Well shielded lighting means less glare, less trespass, and to most people a
more attractive nighttime community.
The POLC codifies standards, including total lumen allowances, that are compatible with
quality lighting design. The total lumen allowances are designed to accommodate basic lighting
needs (such as lighting for safety, utility, security and commerce) in amounts recognized by the
lighting industry (IESNA). The allowances are general and not use-specific, however, allowing
lighting users to make their own choices, using the available lighting allowances according to
their needs and priorities. In primarily residential or rural areas, the allowances are designed
to provide some restrictions for less essential uses such as ornamental lighting, though the
purpose is to effectively limit total lighting amounts, energy use, and light pollution, not to
disallow nonessential uses. When alternative effective lighting practices are available with
differing impacts on the night sky, preference is for standards compatible with the practices
that have the smaller obtrusive impacts. As an example, lighting building façades can be done
from flush in-ground lighting directed upward or from building-mounted light directed
downward: preference is given to the latter because the impacts on the sky are dramatically
decreased, even though this method or design may not be the “standard practice” for some
lighting designers or some franchises.
The technical basis for figures appearing in the MAG POLC that are related to lighting technical
aspects of lighting design or light pollution are described below in some detail. Non-technical
figures related to administrative, legal, or other issues, are more briefly addressed.
S ection 3. Applicability.
Figure: 50%
Type: non-technical
Under Arizona law all lighting legally installed before passage of a new or updated code is
entitled to legal nonconforming status in perpetuity; it need not be modified to meet the
standards of the new or modified code. Reasonable maintenance such as lamp replacement is
allowed without requiring conformance. However, when lighting equipment is replaced or
“significantly” modified, the new lighting must conform to the codes in place when the
replacement or modification occurs. All jurisdictions establish a threshold to differentiate
maintenance from true additions or substantial modifications. In the POLC a threshold of
50% of initial value is suggested to determine when significant modifications or upgrades to
sites requires conformance. A 25% threshold is used in many lighting codes. This threshold
will be discussed and decided upon by each jurisdiction.
Section 4. Outdoor Lighting Standards.
Section 4.1Shielding Standards.
Figures: 2000/1000 lumens; 50’
Type: technical
(The impact of unshielded lighting on sky glow is discussed under Section 4.2.)
To minimize glare and light trespass into residential properties (arising at both commercial-
residential and residential-residential boundaries), unshielded lights on non-residential
properties may not be brighter than 2000 lumens (lm) or located closer than 50 feet to a
residential property line. This is approximately based on the concept of limiting illuminance at
the property line from an unshielded light to 0.06 footcandle (fc), or 2-3x full moonlight. (A
2000 lm lamp is equivalent to about 100 W incandescent or 26 W compact fluorescent.)
The single largest source of complaint related