|The Ottawa Centre's
Light Pollution Abatement Program
by: Robert Dick
This booklet has been used very successfully by the Ottawa Centre to inform non-technical administrators and politicians of light pollution issues. Where "Ottawa-centric" information has been used, the text is in italic. Anyone using this document must insert their own "Centre-centric" information.
A copy of the booklet in electronic form can be down loaded from the Ottawa Centre by contacting the Light Pollution Abatement Committee (LPAC). The file is in Winword 6.0 and is about 45K in size. This does not include image files or graphics.
Users of this document are encouraged to read the articles in two 1997 RASC Journals about Light Pollution Abatement. These are in the August and October Journals.
Figure 1 Comparison of Electricity to Light Conversion Efficiencies
Figure 2 Advantages of Using Sharp Cut-Off Luminaires
Figure 3 Comparison of Illumination Foot Prints from Various Luminaires
This presentation has been produced by the Light Pollution Abatement Committee of the Royal Astronomical Society of Canada (RASC) in Ottawa.
History of the RASC (43k)
The RASC received its Royal Charter from King Edward the VII in 1903. The National Office of the RASC is located in Toronto and co-ordinates the activities of over 3,000 members in 23 centres across Canada. It produces several publications that are distributed around the world.
The Ottawa Centre has over 200 members from all walks of life and has active observing and public education programs. Monthly Centre meetings at the National Museum of Science and Technology are both educational and entertaining and members of the public are welcome. The Centre operates a world famous observatory near Almonte, Ontario. It is used for viewing the night sky by both members and the public. It has been used to discover four comets and it is currently used to introduce astronomy to interested groups in the Region and by members for various projects.
The RASC Light Pollution Abatement Program of the Ottawa Centre is one of several regional programs in Centres across Canada that are addressing the issues of light pollution. The Ottawa Centre's Committee supports a national program. The focus of the Light Pollution Committee is on education and light pollution abatement by providing assistance in the development of environmentally sound lighting policy and procedures both at the municipal, provincial and federal government levels.
This is done through the exchange of ideas in meetings with local officials, offering solutions and recommendations to solve lighting problems, and with programs of awards to progressive communities and governments as well as television exposure.
The Committee firmly believes in the consultative process with the responsible
officials during the early stages of project planning. This has avoided
embarrassing and unnecessary complaints. The Committee is composed of professionals
who recognise the budgetary and political constraints in carrying out lighting
Light Trespass is misdirected light that invades neighbouring property. It creates a nuisance by shining into bedroom windows and other areas. (Light should be directed to where it is needed).
Sky Glow is caused by light scattered off dust and large air molecules over a city. This light was intended to illuminate the ground but, due to poor design, it was misdirected upward into the sky. (It wastes energy and it obliterates the view of the night sky).
Sharp Cut-Off Luminaire (40k), as used in this report, refers to the amount of control the fixture has over the emitted light. It is defined as a luminaire that prevents all light from being emitted above a horizontal plane passing through the lowest portion of the unit. Further, it limits the amount of light directed within 10 degrees below the horizon to less than 10% of the total emitted light. There are two basic versions: flat glass cobra luminaires and shoe box or 'square pack' units.
There are five benefits from well-designed lighting:
If outdoor lights are not properly selected and installed they can be expensive to install and will be costly to operate and maintain. Poor lighting (40k) can also reduce visibility, thereby creating hazards, they can even reduce the security of property and can create an unattractive neighbourhood. They are also harmful to the night environment.
Poor lighting gives rise to the following issues.
Poorly selected and installed lighting causes a glare that can severely hamper the vision of drivers, pedestrians and cyclists, thereby reducing the overall safety of citizens. Glare occurs when the bulb is viewed directly, making our eyes less sensitive to the lower illumination levels around the source.
Poor lighting reduces security by producing dark shadows that can mask danger. It can also reduce the visibility of crimes-in-progress since vandals and thieves do not need their own lights. Officials in Tampa, Florida have reduced vandalism by turning off lights! Without lights, vandals had to use flashlights that were more easily detected by neighbours and patrol cars.
Poor lighting can shine onto neighbouring properties and into windows. This reduces privacy, it can hinder sleep and it creates an unattractive neighbourhood. It is becoming less politically acceptable to tell citizens who complain about the situation to stay away from their windows or to keep their curtains closed from dusk to dawn.
Up to 30% of the light from unshielded luminaries is directed upwards creating adverse effects over our cities and towns. It affects the behaviour of nocturnal animals and birds. The very poor illumination of standard rural 'Yard Lights' wastes even more light. Sky glow symbolises wasted energy and it washes out our view of the night sky, resulting in the loss to the viewer of such natural wonders as the stars and the Milky Way.
An important natural resource and part of our human inheritance is being taken from our children. However, less sky glow means that future generations will be able to enjoy the beauty of the rural environment and our night skies. Children will be inspired, as were past generations, to learn about our world and sky. Perhaps they will study toward careers in engineering and the sciences.
The work of professional and amateur astronomers can be ruined by sky glow as portions of the sky become contaminated by misdirected urban and rural lighting. Operating costs for observatories have increased as dark sites are invaded by sky glow from growing urban centres. The Ottawa Centre has had to abandon two previous observing sites, including their first observatory facility, due to the encroachment of unshielded lights and sky glow. Our present site west of Ottawa is threatened by urban expansion and light pollution from cities and communities in the Region (74k). If the increase in light pollution continues, our present observatory will have to be closed and relocated. Relocation of the observatory will cost the Society about $750,000 for land, new buildings and services!
Poor lighting wastes energy, thus unnecessarily inflating operating costs and environmental pollution from extra transmission lines and power plants. American studies have identified over a billion dollars worth of wasted energy each year because of the light that shines into the night sky. On the local level, a smaller community, with a lower tax base, can have significant savings if efficient lighting is properly installed.
Table 1 Qualitative Comparison of Lamps (59k)
This table compares the qualitative virtues and drawbacks of the different types of lights that are generally in use.
To be complete, the table includes low pressure sodium and mercury vapour lights. The mercury vapour lights have almost entirely been replaced with high pressure sodium or metal halide lights. The low pressure sodium, though apparently attractive in economic terms, are not in wide spread use. It is a monochromatic light source that makes colour recognition impossible and has caused law enforcement and security problems. Also, their large bulb size makes it difficult to shield the light from unwanted areas and it is difficult to focus the light where it is wanted.
The reason for this problem is that the light source is a long tube in which the low pressure sodium gas emits light. The large dimension of the light source is comparable to the size of the focusing optics, making precise control over the illuminated foot print very difficult.
It can be concluded from studying this table that the high pressure sodium lights offer the best overall performance. Their 'warm colour' approximates that of incandescent lights. Thus, if needed for aesthetic reasons, they are a good alternative to the much less efficient incandescent bulbs and are an alternative to the white colour metal halide light sources.
Table 2 Quantitative Comparison of 100 Watt Lamps (46k)
This table provides a numerical comparison of three types of light. The high pressure sodium seems to be the most economical of the three. The data has been drawn from several sources. The Cooper study in Ottawa of high pressure sodium lamps reflects the reduced life that is caused by very cold winters.
The costs have been drawn from American studies ( Lighting Consultants, San Diego, Inc.) and are shown for comparative purposes only.
The colour rendering shows, in quantitative terms, the trade off between low pressure sodium, high pressure sodium and metal halide. Where very good colour rendering is required, metal halide lamps may be selected even though they are more expensive to operate.
Table 3 Cost Comparison of Luminaires (51k)
This table compares the approximate cost for various 150 watts luminaires. These costs are from quotes made by distributors in the Eastern Ontario area based on orders of a dozen or so units. Purchases of larger quantities will only slightly reduce the price. Costs of lower wattage fixtures will also reduce the price. The City of Ottawa pays about $70 for its 70 - 100 watt fixtures.
It would appear that the cost of flat glass cobra head type luminaries are essentially the same as the standard cobra designs. To put this in perspective, it should be remembered that the cost of an installation (luminaire, footing, pole, hydro above / below ground) costs from $2,500 to $5,000.
The use of shields or visors (33k) reduces glare by shielding the light that shines above a horizontal plane that passes through the bottom of the fixture. In terms of the illuminated foot print, this reduces the light that falls far from the installation. However, the illumination at this distance from the pole is only about 1/100 that which falls under the lamp. Therefore, it has a negligible effect on the overall light level distribution and the shield is very effective at reducing glare. The draw back of a shield is that it is must be correctly installed on each fixture and it does not focus the unwanted light to where it is needed.
Figure 1 Comparison of Electricity to Light Conversion Efficiencies
This figure compares the amount of electricity required to illuminate an area with different types of lamps. For example, doubling the illumination without changing the amount of electricity can be accomplished by changing the lamp from high pressure to low pressure sodium, or from metal halide to high pressure sodium (approximately). The figure also shows, at a glance, the improvement in electrical efficiency by changing from mercury vapour and incandescent lights to sodium lamps.
Figure 2 Advantages of Using Sharp Cut-Off Luminaires (10k)
This figure compares the ground illumination level with increasing distance from the pole (dotted line) for both standard cobra luminaries and ones with sharp cut-off optics. Although there is a measurable difference, if you recall the slide that showed the effective illumination along Greenbank Road, south of the Hunt Club Road in the City of Nepean, you'll remember that there was no perceived difference. Figure 3 shows a more quantitative comparison.
Figure 2 also shows the beneficial effects of using focusing optics to direct the light to where is needed (solid lines on the graph). The effect of the scattering lens on standard cobras results in a non-uniform light distribution between two to four pole lengths from the lamp. To the pedestrian or motorist, this appears as a rapid fall off in illumination levels away from the pole.
Figure 3 Comparison of Illumination Foot Prints from Various Luminaires
These two figures compare the illuminated footprints of two sharp cut-off luminaires to that of the standard cobra design (shoe box design (43k) and flat glass cobra (44k)). The optics for these luminaires were selected to provide the best roadway illumination. The sharp cut-off luminaires do not direct light out as far as the standard cobra, however, at a distance of 3 poles, the illumination level is already much less than 1/10 of that directly under the lamp and the slight deficiency is negligible.
A more useful comparison are the levels from one to two pole lengths from the lamp, since, along well travelled streets in the Ottawa area, installations are usually spaced about every four to six pole lengths. The sharp cut-off luminaires have a larger useful illuminated area under the lamp than the standard cobra luminaires. Furthermore, the sharp cut-off designs provide good illumination of the sidewalk behind the pole. This can be exploited to reduce the need for additional installations for only pedestrian use. The nominal extra cost of the sharp cut-off luminaire may be rewarded with fewer installations.
Figure 4 Illumination Distribution for Various Luminaires
These figures are plotted with data from an Ottawa Hydro Study. They show that for a wide pole spacing (48k), the use of Sharp Cut-Off luminaires reduce hazardous glare. For a shorter spacing (58k), illumination levels are as good as or better than for Standard Cobra luminaries.
The increase in our standard of living that began with the industrial revolution is continuing with today's proliferation of advanced technology. This is seen by many as a positive force for beneficial change but it has brought with it some negative effects.
In the past decade there has been increased awareness of the pollution of our air and waterways by toxic chemicals, and other deleterious refuse from our modern society. In addition to the chemical pollution, our sky is receiving light pollution from expanding towns and cities. Along with the physical effects of environmental pollution there is a psychological loss with the degradation of our natural environment. The combined effects of glare, light trespass and sky glow produces an artificial environment in and around our cities and towns. On the economic side, it can contribute to the devaluation of one's home and property by reducing its attractiveness to potential buyers.
Clearly, it would be irresponsible to do nothing while the situation deteriorates. Many progressive communities have started to take corrective action and the RASC is participating in this process.
The selection of proper roadway lights has a major impact on the installation, operation and maintenance cost of the system. It will also define how well it improves the safety and security of the neighbourhood as well as how much it will enhance the appearance of the community. This section provides background information on the selection of roadway lights.
The High Intensity Discharge (HID) Lamps have very concentrated light sources. Typical High Pressure Sodium (HPS) and Metal Halide (MH) bulbs are about the size of a small fist. The source inside the bulb is about the size of the end of a small finger. This compact source is ideal for optics to carefully direct the light to exactly where it should go. However, where it goes and how much goes there depends on the design of the optics in the light fixture.
The manufacturers of lighting systems are very happy to help their clients select the best products for their purpose. They have computer programs that will calculate the ideal spacing and power requirements for a system. The RASC suggest that they be consulted to determine the most cost effective layout for a lighting project.
There are three basic points that should be considered in the layout of street lighting.
2. Safe working conditions require a minimum of amount of light. The installed lights must provide at least this minimum illumination over the specified area.
3. Lights should provide uniform illumination. Large variations in illumination can cause bright areas to effectively mask the areas under lower illumination, thereby masking a potential hazard.
Sharp cut-off luminaires prevent light from being emitted above the horizon. Further, it limits the amount of light that shines within 10 degrees below the horizon to less than 10% of the peak brightness. This reduces the amount of light that shines directly into the eyes of motorists and pedestrians as they look toward the light.
This requirement is not easily achieved with standard cobra head or simple light designs. A now classic example of bad lighting is the use of Yard Lights. These spray light in all directions. Almost a third the light is lost to the sky. Another third is directed at angles that cause extreme levels of glare leaving only 1/3 the light to provide ground illumination. When placed along highways they create hazards by reducing the motorist's view of the road.
Therefore, the town should enforce the phasing out of these unshielded Yard Lights and their replacement with the safer sharp cut-off luminaires.
Minimum Light Levels
Acceptable, average light levels may not create a safe environment. Non-uniform lighting will dramatically affect the required level for safe lighting. The minimum acceptable level is approximately 1/3 the average illumination. This ensures that brightly lit areas do not create a hazard.
The minimum required light level depends on the illumination levels in the neighbourhood. An otherwise adequately illuminated corner may appear pooring lighted if a business is opened with extremely bright lights or produces a great deal of glare. "Adequate' lighting may require the town to 're-lamp' with much brighter street lights than previously required. This cost would be borne by the town. To avoid this re-lamping cost, after street lighting has been installed, future lighting must not be allowed to create a hazardous condition through glare or excessive light levels.
Therefore, the town should exercise control over the type of luminaires and the illumination level around businesses and homes to ensure that safe lighting is maintained. This should be done by a lighting policy.
The standard cobra luminaires distribute light through the scattering of light in its bulbous lens beneath the fixture. The scattering process is, by its nature, somewhat random and poorly controlled. Typical illumination patterns under a standard cobra head show high levels of illumination and a rapid fall-off further away. A series of closely spaced installations (every two or so pole lengths) are required to provide uniform illumination along a street. High wattage lamps are required to maintain minimum levels of illumination between poles. There is little flexibility with the standard cobra head lens.
New luminaires provide much more control over where the light is directed. These designs distribute the light more uniformly between the poles, providing more uniform illumination and allowing wider separation yet maintaining good illumination levels along the road. Fewer installations may be required with modern luminaires.
The modern luminaires, such as the "shoe box" or square pack designs using reflective optics, focus the light onto the edges of the illuminated footprint. This is one of the exciting features of modern lighting technology. Indeed, these new luminaires are slightly more expensive than the standard cobra head but they effectively limit glare by placing the light where it is intended, and fewer installations may be required thus reducing the overall system installation, operating and maintenance costs.
Although not as efficient at focusing the light, flat glass cobra luminaires are less expensive and their cooling design is more similar to that of the standard cobras. Richmond Hill, Ontario finds that they have slightly longer life expectancy than the 'shoe box' designs.
Most manufactures market luminaires that carefully control the placement of the illumination footprint. These products offer improvements over the standard cobra head design.
In this report the unit installation costs for outdoor lighting are considered to be constant since they will be approximately the same for the wiring (above or below ground), pedestals and poles (wooden, concrete or spun aluminium) regardless of the type of luminaire mounted on the pole. However some of the more expensive luminaires, with well designed optics, may result in a lower system cost by reducing the number of installations required for the same quality of illumination (minimal glare and good uniformity).
Modern sharp cut-off luminaires using reflective optics provide more uniform illumination on the ground. By reducing the maximum brightness under the lamp, a more pleasing and effective illumination can be achieved with the same or lower wattage lamp.
In addition to the glare they cause, the Yard Lights are wired to remain on from dusk to dawn. No one will notice someone passing across the yard unless people are awake. Although modern luminaires are more expensive, they may be purchased with motion sensors so that they turn on only when necessary and actually act as visual alarms to property owners, vandals and prowlers. The energy they save, even for incandescent bulbs, and security they offer, will pay for the increased cost within a few years.
Therefore, the town should actively encourage the use of motion detectors
on security lights and to discourage the use of "dusk to dawn" timer switches.
Many communities in Ontario have already upgraded their old fixtures with High Pressure Sodium lamps, but they have not upgraded to sharp cut-off luminaires or retrofitted older units with shields or visors that minimise glare, light trespass and sky glow. An analysis of the information produced for this presentation reveals that:
1. PURPOSE OF PRESENTATION (35k)
Measurement > Education
Abatement > Awards
Glare: The visual discomfort resulting from insufficiently shielded light sources in the field of view. It reduces a person's ability to see details not directly illuminated by the light. This degrades safety and security. (One should see the ground, not the light source).
Replacement of Standard Cobra Head Luminaires
Adoption of Sharp Cut-Off Luminaires
Flat Plate Cobra Head or Square Pack Designs
Visors for existing Cobra Head Luminaries
This page last modified: August 30, 1998