The Challenges of Exterior Lighting
Seeking enhanced safety and appearance, facilities look for
technology and products that also deliver quality lighting cost-
effectively
By John L. Fetters
Email the MS editors.
A growing number of education, medical and other institutional and
commercial organizations are using their facilities at night, so
effective nighttime lighting is essential for illuminating walkways,
automobiles and obstructions. Proper lighting also provides security
for visitors and occupants who are walking, driving or biking. It
helps accentuate building entrances and signage, and it provides an
attractive outdoor environment with no glare.
Facilities with quality outdoor lighting are safer when pedestrians
and drivers can see better, and quality lighting produces an
attractive nighttime environment. Quality lighting fixtures provide
well-controlled light distribution, and they do not produce glare.
But managers responsible for providing and maintaining good outdoor
lighting for parking lots, parking garages, storage areas and
walkways face a number of challenges in specifying products that
produce effective outdoor lighting.
Good lighting vs. bad lighting
Most outdoor lighting installations provide more bad lighting than
good. Bad outdoor lighting is counterproductive, reducing safety and
security and creating higher-than-normal operating costs. Poorly
designed, misapplied, defective, improperly located or badly aimed
fixtures can cause glare, harsh shadows, wasted light and light
trespass.
Such fixtures are easy to spot at night because they produce
obtrusive light or glare. Obtrusive light is the generalized
category of unwanted light that includes sky glow and light
trespass, which causes annoyance, discomfort, distraction or
reduction in the ability to see. Light trespass is obtrusive light
that crosses a property line.
Many people mistakenly believe that a great deal of glare means
there is a great deal of light. Actually, glare is an indicator of
inefficient and ineffective light. Glare never aids visibility.
While glare is rather subjective, in most cases all that is needed
to prevent it is to select the correct luminaire optics, use the
correct pole height, put the pole in the correct place, and use
shielding accessories where required.
The best way to minimize glare and prevent obtrusive light is to
replace offending fixtures with full-cut-off fixtures, which have no
up-light or glare and, when they use energy-efficient lamps, are
energy efficient. Cut-off fixtures are designed for streetlights,
parking lots, garages and pedestrian walkways.
Well-designed, full-cut-off fixtures prevent light above the
horizontal plane that causes "sky glow" and usually are energy-
efficient. The Illuminating Engineering Society of North America
(IESNA) recommendations for such fixtures can be found in RP-
33, "Lighting for Exterior Environments."
One new streetlight or roadway luminaire designed to replace the
glary cobra-head design is the mongoose, which is designed to
provide superior optical performance and reduce maintenance costs.
Lighting solutions
The primary purpose of lighting parking lots is to benefit
pedestrians, according to IESNA. The design intent requires that a
driver or pedestrian who looks at the brightest spot in the field of
view also can see an object in the dark areas within the field of
view. Light levels must be balanced to provide the uniformity
necessary to produce this result. White-light sources also help
drivers find their cars by enabling them to identify colors more
accurately.
Wall-mounted wall-packs are available with cut-off optics and can be
used to light narrow parking areas between or adjacent to buildings.
They are available in a variety of architectural styles and should
be mounted no higher than 25 feet.
Managers also can specify bollards which look like short, thick
posts to effectively light walkways and building entrances. Low-
wattage metal halide or compact fluorescent lamps (CFL) also are
options for primary light sources. Managers should ensure that
bollards and ground-mounted floods are protected from lawn mowers
and snow-removal equipment.
Floodlights often put light in people's eyes and are another common
source of direct glare. But even well-designed floods must be
installed properly, with beams aimed so they do not cause glare.
Wall packs also can be a source of glare unless they are designed
with good light control.
Globe fixtures look good in the daytime, but because they tend to
deliver a high amount of light above the horizontal centerline, they
are a source of light pollution. Another source of light pollution
is sign lights that are aimed to light from below. Especially on
foggy mornings, the beams of these floodlights can project over
signs, lighting the sky.
Lighting trends
Too much light is a common cause of bad outdoor lighting and can
impair visual adaptation. When people move from areas that are too
bright to those that are too dark and vice versa poor visibility
results. When lighting designs do not minimize the effect called
transient adaptation, the steep transitions of light to dark inhibit
visibility.
The trend in outdoor lighting is toward white light with a good
color rendering index (CRI). The use of yellow or orange low-
pressure where the CRI is 0 and high-pressure where the CRI is
25 sodium lamps has been declining for some time. There is also an
increase in visual acuity when lamps that are scotopically enhanced,
such as metal halide lamps with higher color temperature more than
4,000 K that are the most popular white-light source for outdoor
lighting.
Also, sales of pulse-start metal-halide lamps are starting to
outpace those of standard metal halides because of improvements in
efficiency, restrike time and color consistency. They also have good
CRI values of 7080.
Some higher-wattage CFLs are being used in walkway and entrance
fixtures. They are energy-efficient, deliver long life and have good
CRI values, in the low 80s. For outdoor applications in northern
climates, managers might consider amalgam lamps most triple tubes
are amalgam to maintain lumen output at low- and high-temperature
extremes. Managers should ensure that they are used in enclosed
fixtures and close to a building to minimize the effects of low
temperatures and wind chill.
Long-life, white, electrodeless lamps are finding applications in
roadway and walkway lighting, and they offer managers an option that
reduces maintenance labor costs. Electrodeless lamps also have good
color rendering with values in the mid-80s, similar to fluorescent
lamps.
Managers should avoid using obsolete mercury-vapor lamps for outdoor
lighting. They have severe lumen depreciation, they seem to burn
forever, even with very little light output, and they have poor
color rendering, with values of 2252.
Managers need to ensure that outdoor lighting systems are controlled
so they can be turned off when they are not required. The best
control is a photocell, an electrical switching device that operates
when light falls on it. Photocells are used to turn on lighting at
dusk and turn it off at dawn. They have a built-in time delay, so
they will not turn off a lighting system when lightning flashes at
night.
When photocells fail, they fail on, or fail-safe. So, when an
outdoor lighting system controlled by a photocell is on during
daylight hours, the photocell usually has failed.
In the northern hemisphere, managers should make sure photocells are
aimed north to "see" the reflected light of the northern sky so they
are not influenced by the directionality of east/west exposure or
degraded by intense southern exposure.
The least expensive type of photocell uses cadmium-sulfide cells
that degrade from exposure to sunlight and lose sensitivity after
being in service for a few years. This loss of sensitivity decreases
savings by keeping exterior lighting on longer than necessary.
To avoid this loss of energy savings, managers should replace
cadmium-sulfide cells with electronic cells that use solid-state,
silicon phototransistors or photodiodes, which do not lose
sensitivity over time. Also, solid-state photocells last longer, as
evidenced by their longer warranties up to six years and pay
back before that time in energy and labor savings.
Finally, managers can use time clocks or energy-management systems
to limit outdoor lighting within certain hours during the night when
some systems can be turned off.
Improvements in lighting equipment especially luminaires with
excellent cut-off optics and new white-light sources are available
to help managers relight their facilities' exterior areas.
Relighting with quality equipment can produce better visibility for
facility visitors and occupants and make outdoor environments both
more attractive and safer.
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