DA, October 1992
What is Quality Roadway Lighting?
The notion of "What Is Quality Roadway Lighting" is often very subjective depending on whether
your are a public works official, a street lighting designer, street maintenance and repair
manager, citizen, resident, business person, pedestrian, vehicle driver, or an astronomer.
There are a number of different factors that the above parties may think about with respect to
roadway lighting. Depending on perspective, there may be a wide variation in the priority given to
these factors. In the final analysis, they are all important to yield quality roadway lighting.
A brief summary of factors which contribute to, affect, or are affected by quality roadway lighting
includes:
Design Standards : Generally, public agencies (villages, townships, cities, counties, and
states) are responsible for establishing design standards to be applied within their
jurisdiction. The design standards vary widely, from "placing a light here if it is needed" to
legislated compliance with IES minimum recommended standards.
1.


Design standards may be expressed in illuminance, luminance, or visibility criteria.
Separate standards may be established for roadways, pedestrian walkways, adjoining or
separate bikeways, or equestrian paths. These design standards, based on various
parameters and preferences of the local agency, will dictate combinations of mounting
heights, lamp size, and pole spacings.
Energy Standards : Depending upon the design standards selected and the lamp type and
size selected, the energy requirements for roadway lighting will vary widely from one project
to another. Then for any particular system, there may be significant variations between
2. Information Sheet 61 (June 2000)
http://www.darksky.org/resources/information-sheets/is061.html
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initial energy requirements immediately after construction of a new roadway lighting system
and long term service life energy requirements.


The energy requirements and the relative cost of energy from the local utility company may
become an important factor in design standard decisions.
Physical Characteristics : Quality lighting for a reasonable service life will depend on quality
components to be used in the physical street lighting system. This includes:
3.
Poles manufactured to a standard that will last 30-50 years (including welds,
brackets, arms, coatings, and other accessories).
Luminaires, with special care given to hinges, latches, gaskets, and accessibility for
maintenance and cleaning. Luminaires should have an expected service life, taking
into account local atmosphere conditions, of 15 years or more.
Optical Characteristics : Quality lighting is highly dependent upon proper selection of the
optical distribution of light on both horizontal and vertical surfaces, with care taken to
manage and control glare and minimize light trespass (which is defined as unwanted spill
light onto adjacent or nearby property), and light pollution (which is defined as stray light
emitted into the sky which depreciates the view of the nighttime sky for the public or
astronomers).
4.


Color spectrum of the lighting source is also important from different perspectives. Citizens,
businesses, law enforcement officials, and others generally desire good quality color
rendition of objects and people.
Operating Controls : Many old street lighting systems, and occasionally new ones, are
operated by a time clock. This is advantageous because all lights are turned on and off at
the same time, giving the system a uniform appearance during that time of day. It will turn
the lights on and off at exactly the same time of day regardless of atmospheric conditions
such as clouds, fog, etc., a fact which is not considered an advantage.
5.


The more appropriate method used now for turning streetlights on and off is the
photoelectric cell (PE) operated switch. These PE cells are installed individually on each
luminaire. There are several grades of quality of these switches. The primary advantage of
the PE cell is that even though one cell or another may fail completely, the entire circuit
does not depend on any one controller, as would the clock described above.
Another advantage is that the PE cell will recognize light or darkness due to atmospheric Information Sheet 61 (June 2000)
http://www.darksky.org/resources/information-sheets/is061.html
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conditions other than sunset and sunrise and will turn the lights on or off whenever the
ambient light reaches the appropriate level.
A disadvantage, particularly with a lower quality model, is that the sensor will "drift", usually
leaving lights on longer in the morning or turning them on earlier in the evening. The
accumulation of this drift can represent a significant increase in the cost of energy for the
responsible agency. Each of the above operating factors and quality considerations should
be taken into account in the design of a quality roadway lighting system.
Field Conditions : Quality lighting can often be seriously and detrimentally affected by a
variety of field conditions, all of which should be addressed. These include:
6.
Vertical and horizontal alignment of the roadway.
Trees, shrubs, and related foliage, which may interfere with efficient and effective use
of the lighting.
Proximity of bedroom windows and other areas which require special control of the
light output.
And many other factors which must be appropriately considered to assure quality
lighting on the roadway and walkways for its intended purpose without giving negative
impact as well.
Aesthetics: The physical appearance, in both daytime and nighttime, often becomes a
sensitive and sometimes emotional issue. It is subjective and sometimes has
psychological overtones. Aesthetic considerations which determine the "quality" of the
roadway lighting system may include the scale of the equipment used and the symmetry of
the design. Physical aspects such as pole style, color, and finish materials, shape, height,
and luminaire type and size are often factors of sensitivity within the community.
7.


Subjective also are the color of the light source, and from an aesthetic point of view, the
control of glare, effective control over light for its intended purpose, and the appearance of
light trespass and light pollution.
Maintenance Practices : When the factors discussed above have been considered relative to
selection and installation of a lighting system, the long term task of maintenance,
operation, and repair begins. To assure longevity of a quality lighting system, maintenance
practices must be specified to renew or rejuvenate the system and to prevent a steady, long
term decline in the level of lighting service. These practices include:
8.
Spot replacement of lamps
Group replacement of lamps
Cleaning of reflectors and refractors
Painting of poles, where appropriate
Replacement of damaged poles, glassware, and luminaires
Tree trimming, if appropriate
The objective of providing quality roadway lighting must be accompanied by a strong
commitment to a sound maintenance program. Too often, good roadway lighting systems
are built and quickly become a source of complaint due to lack of adequate maintenance
resources or inadequate practices and procedures. Information Sheet 61 (June 2000)
http://www.darksky.org/resources/information-sheets/is061.html
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Liability Impact : It is generally understood by most legal counsels that public agencies
have no liability for lighting if no lighting is yet installed. Once installed, the courts generally
hold the agency or owner liable for maintaining the lighting system to the level to which it
was designed.
9.


This brings home the importance of selecting an appropriate standard, designing to that
standard, and maintaining to that standard. Failure to do these things will generally
increase the agency's or owner's liability, because they will fail to prove that they have been
responsible in administrating their system and will generally be held liable for all or part of
the claims against them relative to poor lighting.
Costs: Ultimately, quality lighting will have a cost associated with it. Each and every factor
discussed above will contribute towards that cost. There are two distinct and different costs;
one directly affects the other. First is the cost of installation. Depending on the design levels
selected, pole and luminaire size, type, style, architecture, color, and finish all result in the
initial cost of the installation. Second is the long term maintenance cost for the service life
of the system. It is basically composed of three components:
10.
Energy costs
Replacement cost of components
And the labor involved in replacing lamps, repairing deficiencies, and installing
replacement parts.
Decisions made in the design stage and in equipment selection will be major factors in
determining both type of costs. Most often, deterioration of quality lighting results from lack
of resources to maintain the system in the manner in which it was designed, because of
the high cost of replacement parts or the labor required to maintain the system.
It can be readily seen that quality lighting is more than just putting up a pole "right here" and
attaching a lamp. It requires consideration of many different factors, from initial decisions on
appearance, service levels, and the commitment of resources to maintain the system in
operation as it was designed. A quality roadway lighting system should meet the objectives and
should avoid the objections of a wide vari