design elements - San Jacinto Texas Historic District

Lighting Effi ciency & Pollution Control Methods
Defi nition
Exterior lighting systems can improve the
safety of pedestrian and vehicular circulation,
aid surveillance and increase perceptions of
safety, and enhance retail environments. The
most common type of exterior fi xture is the
street light, which is available in a variety
of pole heights and luminaire shapes to suit
both street and pedestrian uses.
By some estimates, street lights account for
approximately 40% of a typical city’s electrical
consumption. For this reason, energy
effi ciency is an important objective for most
lighting designs. Designs that greatly exceed
minimum illumination standards may be
wasting energy. The choice of lamp type also
aff ects the amount of energy needed (watt s) to
produce the required illumination (lumens).
Light-emitt ing diode (LED) technologies
are emerging that promise to provide
more lumens per watt of energy consumed
than other lamp types. LED’s also off er the
advantages of a long lamp life, good color
rendering, and improved directional control.
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Improperly designed lighting systems
can also contribute to light pollution. The
International Darksky Association and its
local Texas affi liate (www.darksky.org and
www.texasida.org) describe Light Pollution
as “any adverse eff ect of artifi cial light
including sky glow, glare, light trespass,
light clutt er, decreased visibility at night, and
energy waste.” Upward facing light fi xtures
are one of the primary contributors to light
pollution. To address this issue, the American
National Standard Practice for Roadway
Lighting identifi es four classifi cations of
luminaires: Noncutoff , Seimcutoff , Cutoff ,
and Full Cutoff . They each allow a decreasing
intensity of light (as measured in candelas
per 1000 lamp lumens) above 80 degrees and
above 90 degrees (from vertical). A full cutoff
luminaire permits no light to leave the fi xture
above 90 degrees and is the only fi xture type
that does not directly contribute to light
pollution.
Applicability
The American National Standards Institute
(ANSI) and the Illuminating Engineering
Society of North America (IESNA) jointly
Parking lot lighting design.
IMAGE: HOLOPHANE