Page 110 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED Sustainable Sites 91

at the site boundary and no greater than 0.01 horizontal footcandles 10 feet beyond the site
boundary. Document that no more than 2% of the total initial designed fixture lumens are
emitted at an angle of 90 degrees or higher from nadir (straight down). For site boundaries
that abut public rights-of-way, light trespass requirements may be met relative to the curb
line instead of the site boundary.
LZ3 – Medium (Commercial/Industrial, High-Density Residential)
Design exterior light so that all site and building mounted luminaires produce a maximum
initial illuminance value no great than 0.20 horizontal and vertical footcandles at the site
boundary and no greater than 0.01 horizontal footcandles 15 feet beyond the site. Document
that no more than 5% of the total initial designed fixture lumens are emitted at an angle of
90 degrees or higher from nadir (straight down). For site boundaries that abut public rights-
of-way, light trespass requirements may be met relative to the curb line instead of the site
boundary.
LZ4 – High (Major City Centers, Entertainment Districts)
Design exterior lighting so that all site and building mounted luminaires produce a
maximum initial illuminance value no greater than 0.60 horizontal and vertical footcandles
at the site boundary and no greater than 0.01 horizontal footcandles 15 feet beyond the site.
Document that no more than 10% of the total initial designed site lumens are emitted at an
angle of 90 degrees or higher from nadir (straight down). For site boundaries that abut
public rights-of-way, light trespass requirements may be met relative to the curb line instead
of the site boundary. LEED 2009 also allows for a single luminaire at intersections of private
driveways and public roadways in all the zones. At this location, the requisite site boundary
is modified so that the maximum allowed footcandles may go beyond the actual site
boundary to the centerline of the street for an area with a width of twice the driveway
width.
Potential Technologies and Strategies
Adopt site lighting criteria to maintain safe light levels while avoiding off-site lighting and
night sky pollution. Minimize site lighting where possible and model the site lighting using
a computer model. Technologies to reduce light pollution include full cutoff luminaires,
low-reflectance surfaces and low-angle spotlights.

Calculations and Considerations
To obtain a point for this credit in either version, one of the two interior lighting requirement
options and all the applicable exterior lighting requirements must be met. The interior
lighting requirement options are the same regardless of the use of the site or the location of
the site. The exterior lighting requirements vary depending on site use, use density, and
location. The exterior lighting requirements are divided into two main portions: the first
limits the exterior lighting density, and the second limits the light distribution, particularly
beyond the site, either over the property lines or upward into the heavens. Note that in all
cases, it is important to try to interpret between existing standards and design for the lowest
possible light levels while addressing safety, security, access, way finding, identification,
and aesthetics.

Interior Lighting Requirement This requirement is very simple and can be met in two
different ways. Interior lights should not shine out directly through windows or other
openings in the building envelope, be they translucent or transparent. If they do, then
all interior lighting other than emergency lighting shall be on automatic controls (with
manual overrides) to be turned off during nonbusiness hours for LEED 2.2, or either
have automatically reduced input power or shielding at the opening to the building
envelope between 11 p.m. and 5 a.m. for LEED 2009.