Landscape Architect Articles

Lighting the Dark Sky04-01-03 | News

Lighting the Dark Sky

A view of a major Tucson street showing properly directed lighting on the street and in the parking lots (i.e. no glare, no direct up light and comfortable lighting levels). Note also the correct use of lighting at the tennis facilities in the background as compared to the bad, glary lighting at the swimming pool in the further background.???????(R)?EUR??,,????'?EUR??,,?EUR Images for this article are provided courtesy of the International Dark-Sky Association (www.darksky.org)

Imagine a time, long ago . . . or not so long ago . . . or even existing in some places around the world today . . .Wild animals roam throughout the land and a roving band of natives has successfully hunted down tonights dinner. As the fire is prepared, the harrowing roar of a nearby predator pierces the evening calm . . . followed by another from within the forest and another from beyond the pond . . . It will be a long night ahead. The fire will have to be built high . . .

As the sun sets, several of the party are working busily over and around the fire. Some are tending to the palette of roasting nourishment. Others work to keep the flames high and the light bright enough to shine past the third or fourth row of trees. They are careful not to get too close, nor to lose their tools in the shadows of the stone-lined pit . . . others are looking away from the fire and into the night . . .

Blinded by the glare of an exposed luminaire, a pedestrian could easily fall victim to the criminal hiding in the shadow of the parked vehicle.

Since the first day that a fire illuminated the night man has pondered the question of how to get enough light to do what?EUR??,,????'?????<

At the ASLA Annual Convention in 2002, light pollution and the continuing growth of the ?EUR??,,????'?????<

Same view, but with a flash photograph to show where the criminal is.???????(R)?EUR??,,????'?EUR??,,?EUR Eliminating the glare can allow the eye to see into the shadows.

In this first of many articles on the subject, LASN begins with an outline the basic outdoor lighting concerns as put forth by a National Electrical Manufactures Association?EUR??,,????'?????<In addition LASN, invites you to participate in this ongoing discussion by visiting landscapearchitect.com. Following the ?EUR??,,????'?????<

According to the NEMA White Paper there are three primary issues concerning outdoor lighting; Sky Glow, Light Trespass and Glare. While Light Glow is primarily a concern for the scientific or the recreationalist, Light Trespass and Glare are elements that should be factored into any new landscaped development.

Sky Glow resonates from the concentrated lights of a city. Notice the poorly directed lights from residences on the hillside facing the photographer.

As such, here are excerpts from the NEMA White Paper on Outdoor Lighting Code Issues:

Sky Glow / Light Pollution

Sky glow is the haze or ?EUR??,,????'?????<

Light Trespass

Light trespass occurs when neighbors of an illuminated space are affected by the lighting system?EUR??,,????'?????<

A similar view of the same area as seen on page 85, after the re-lighting of the swimming facility.

A common cause of light trespass is the inappropriate selection, tilting or aiming of outdoor luminaires for the particular lighting task. Light trespass occurs when a luminaire emits too much light at high angles or projects light too far from where it is intended. Even luminaires that are designed to control their light output can be light trespass offenders when improperly applied within a lighting design.

Light trespass can be minimized through careful selection of lamp wattage, luminaire type, and placement. Appropriate reflector selection, aiming and shielding of the luminaires is critical to keep the projection of the light within property boundaries. When using floodlights or wallpacks in areas close to adjacent properties, select products that utilize advanced optical techniques to minimize light trespass.

Decorative pole-top lighting fixtures, as pictured above, may look great in the daytime. However, at night, without proper shielding and light trespass precautions, globe lights can waste energy by throwing light into the sky. In addition glare is almost always a factor with these types of fixtures.

Non-cutoff luminaires will not have a significant impact on light trespass if the light does not project far from the luminaire location.

Glare

Glare occurs when a bright source causes the eye to continually be drawn toward the bright image or the brightness of the source prevents the viewer from adequately viewing the intended target. Glare may create a loss of contrast or an afterimage on the retina of the eye reducing overall visibility.

Two classifications of glare are discomfort glare and disability glare. Discomfort glare does not necessarily keep the viewer from seeing an object but does cause a constant adaptation of the eye to the contrast of light levels that in turn may cause a sensation of discomfort.

Non-shielded flood lights can throw light in unnecessary directions creating sky glow and wasting energy.

Disability glare occurs when the bright source causes stray light to scatter in the eye which causes the primary image on the retina to be obscured. It may prevent the viewer from seeing things of importance.

There are two distinct situations when glare occurs:

When a spot in the field of view is significantly brighter in contrast to the rest of the field of view. An example is when a bright direct or reflected lamp image is visible.
When a significant difference in light levels exists between adjacent areas. An example of this is when a person leaves a brightly lighted gas station and reenters the roadway it may take minutes for the eyes to adapt to the lower lighting levels.

Full cutoff and cutoff luminaires can help prevent the direct image of a bright source and lower the intensity of the light at high angles. Luminaires may be equipped with louvers and/or exterior visors to prevent viewing a bright source at lower angles, though this may effect the spread of the distribution. Additionally the use of quality prismatic or opaque lens materials can spread the bright image over a larger area and reduce the brightness of the source.

Full cut off fixtures deliver proper lighting levels and conserve energy by only using enough energy to light a targeted area. In addition, since the eye is not compromised by glare, less overall lighting is needed to provide safety and security.

Maximum mounting heights are required for proper aiming of floodlight luminaires to reduce glare in an adjacent, unintended, field of view. It is important to conform to ambient light levels based on the environment of proposed installation. Even lighting designs intended to comply with local codes or master store specifications may need to be adjusted to accommodate the specific surrounding environment.

Effective design techniques for outdoor lighting include:

Defining lighting criteria based on the demographics for the area. There are distinct differences in the lighting requirements between urban and rural areas. Many codes and guidelines reference these areas as ?EUR??,,????'?????<
Confining projections of light and glare to within property lines.
Using pole heights appropriate to the application.
Utilizing a shield that minimizes the component of light above horizontal and glare when luminaires need to be tilted or aimed. Avoid tilting cutoff luminaires.
Utilizing control systems to reduce light levels during inactive periods or at predetermined times late in the evening while maintaining sufficient lighting for safety and security. Roadway luminaires should not be switched off at night.
Designing the spacing of poles such that the illuminance on the ground is uniform, thereby increasing safety and security, while minimizing reflected light into the night sky.
Providing adequate vertical illuminance helps to provide better visibility of automobiles and pedestrians for increased safety and security.
Defining illuminance targets based on IESNA recommended guidelines.

Excessive illuminance levels may increase the likelihood of sky glow, light trespass and glare. Adaptation difficulties may exist when leaving a brightly-lighted area to the darker roadway. Use of excessive lamp wattage and specification of excessive illuminance wastes energy.

To the Future

Given that, as a whole, we need light to function as a society, it is in our best interests to give careful consideration to the planning of outdoor lighting. As such, it is important to plan ahead for proper use of light direction and energy consumption. While NEMA?EUR??,,????'?????<

About NEMA

According to its website, the National Electrical Manufacturers Association (NEMA) was created in the fall of 1926 by the merger of the Electric Power Club and the Associated Manufacturers of Electrical Supplies, to provide a forum for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective, and compatible electrical products.

Excellent full cutoff wall packs, illuminate the sidewalk and stairways.

The association promotes safety in the manufacture and use of electrical products, provides information about NEMA to the media and the public, and represents industry interests in new and developing technologies.

NEMA, with headquarters in Rosslyn, Virginia, has over 400 member companies, including large, medium, and small businesses that manufacture products used in the generation, transmission and distribution, control, and end-use of electricity. Annual shipments of these products total $100 billion.

A prime example of quality sports lighting, using excellent lighting fixtures with good control of light output. As a result, there is minimal glare for the players and spectators, and no complaints from neighbors relative to light trespass.

NEMA’s mission is to promote the competitiveness of its member companies by providing quality services that will impact positively on standards, government regulations and market economics.

Useful Industry Websites

Illuminating Engineering Society of North America www.iesna.org
International Association of Lighting Designers www.ialo.org
National Council on Qualifications for the Lighting www.nlqlp.org
National Electrical Manufacturers Association www.nema.org
International Dark-Sky Association (IDA) www.darksky.org

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NEMA’s Luminaire Section, Outdoor Lighting Task Force has put together their recommended Model Outdoor Lighting Regulation February 2003

Following are excerpts of that model:

Purpose:

The regulation promotes good lighting practice consistent with energy conservation, safety needs, and preservation of the natural night environment. The regulation defines the conditions under which State funding may be used to install or replace outdoor lighting. The principles embodied in this regulation to achieve those ends include the reduction of wasted light, glare, and trespass, and use of minimum appropriate light levels. The regulation achieves those ends by requiring lighting devices with improved light control while providing latitude for qualified professionals to provide a variety of solutions to lighting needs.

Definitions:

In this regulation terms shall mean the following:

Luminaire: a complete lighting unit, often referred to as a ?EUR??,,????'?????<

Lamp: the component of a luminaire that produces light; the light source.

Lumen: a standard measure of luminous flux representing the quantity of visible light output.

Artificial night sky brightness due to light pollution in North America is shown as a progression from real data in 1950 to projected levels in 2025. Photo is courtesy of the International Dark-Sky Association and W.T. Sullivan with data provided by the Defense Meteorological Satellite Program.

Candela: a unit describing the intensity of a light source in a specified direction.

Nadir: the point directly below the luminaire defined as 0 degrees vertical angle.

Maintained Illuminance: the amount of light per square area required or recommended for a lighting application, taking into account losses over time between relamping and cleaning of the luminaire.

Outdoor Luminaire: any type of fixed or movable equipment that is designed or used for outdoor illumination. The term includes street lighting and area lighting, The term does not include lighting that is required to be installed on motor vehicles or lighting required for the safe operation of aircraft.

A full cutoff lighting fixture in the fog, showing the excellent control of light output. Since there is no glare, visibility is good in the fog, and the lighting system helps rather than hurts visibility.

Full Cutoff Luminaire: a luminaire that allows zero candela at or above an angle of 90 degrees from nadir and candela at 80 degrees vertical angle above nadir that is no more than 100 per 1000 lamp lumens.

Energy Conservation: reducing energy costs and resources used, and includes using less luminaires and/or using luminaires with lower wattage consumption and using control technology to turn off or reduce wattage consumption of luminaires under appropriate circumstances.

Glare: light emitting from a luminaire that causes reduced vision or momentary blindness.

Light Pollution: the night sky glow caused by the scattering of artificial light in the atmosphere.

Light Trespass: light emitted by a luminaire that shines beyond the boundaries of the property on which the luminaire is located.

Low Pressure Sodium (LPS) lights were supplemented with 10% white light to better show the true colors of the cars in this new car lot.

Qualified Lighting Professional: an Engineer or Lighting Designer trained in outdoor lighting design and a person certified as Lighting Certified (LC)by NCQLP.

Standards for State-Funded Outdoor Lighting:

An outdoor luminaire may be installed or replaced using state funds only if:

The new or replacement outdoor luminaire is a full cutoff luminaire, or a luminaire that permits no more than 2% of the total luminaire lumens in the zone of 90 to 180 degrees vertical angle, if the rated output of the luminaire is greater than 3200 lumens;
The minimum average maintained illuminance adequate for the intended purpose is used, with consideration given to nationally recognized standards, including, but not limited to, recommended practices adopted by the Illuminating Engineering Society of North America (IESNA);
For lighting of a designated highway of the state highway system, the State Department of Transportation determines that the purpose of the outdoor luminaire cannot be achieved by the installation of reflective road markers, lines, warning or informational signs, or other effective passive means;
Full consideration has been given to energy conservation, reducing glare, minimizing light pollution,minimizing light trespass and preserving the natural night environment;
When within a ?EUR??,,????'?????<

Additional Factors per the IDA

Following is an excerpt from the International Dark Sky Associations recommended Ordinance language:

2.2. CONTROL OF GLARE—LUMINAIRE DESIGN FACTORS:

A. Any luminaire with a lamp or lamps rated at a total of MORE than 1800 lumens, and all flood or spot luminaires with a lamp or lamps rated at a total of MORE than 900 lumens, shall not emit any direct light above a horizontal plane through the lowest direct-light-emitting part of the luminaire.

B. Any luminaire with a lamp or lamps rate at a total of MORE than 1800 lumens, and all flood or spot luminaires with a lamp or lamps rated at a total of MORE than 900 lumens, shall be mounted at a height equal to or less than the value 3 + (D/3), where D is the distance in feet to the nearest property boundary. The maximum height of the luminaire may not exceed 25 feet.