Robert Dick

M.Eng., P.Eng.
P.O. Box 79
Rideau Ferry, Ontario
K0G 1W0
CANADA



Contributions:


Royal Astronomical Society of Canada, Light Pollution Abatement Program
RASC Dark Sky Preserve Program
RASC Urban Star Park Program
Parks Canada Guidelines for Outdoor Lighting
Promotion of less intrusive urban lighting
Development of the CSbG Luminaire

Light Pollution

We have become use to several forms of urban pollution: air, water and noise. But there is one other form that is ubiquitous and, until recently, has been believed to be benign.

Light pollution is the combined effect of glare, light trespass and sky glow. Although artificial lighting is used to increase visibility and safety at night, in many cases light pollution can actually reduce the safety and security it is intended to provide. The main culprit is the light that is directed to where it is not intended.

Light pollution is more than just a nuisance for stargazers and astronomers. Without the contrast between the day and a dark night, our health can be compromised as well. Check out my link to scotobiology. Thirty years ago we were unaware of this problem, and we were coping with the expensive solutions to air and water pollution. But we know about light pollution and we must reduce it. Fortunately, the solutions are inexpensive and readily available.

If we are successful, our children and grandchildren will thank us.

Solutions

Although air and water pollution were expensive to reduce, light pollution is very cheap. The first key is to recognize there is a problem. The second is to understand the problem. And the third is to apply cost effective measures to reduce it. As with air and water pollution, these include changing the ways we use light. We have now reduced the amount of contaminated air and water that is released into the environment. So we should now address light pollution.

The four tenets for reducing the impact of light on the environment are to limit the:

  • extent of illumination with shielding
  • level of illumination with lower wattage lamps
  • duration of illumination with timers, and
  • colour of illumination with the type of light.

It is a remarkable time we live in, that all these requirements are so easily adopted. Not only will they reduce the impact of light pollution on the environment, but they will also reduce our energy consumption. Every joule of energy we save and lumen we reduce will help.

3 FORMS OF LIGHT POLLUTION

Glare
is the visual discomfort resulting from insufficiently shielded light sources in the field of view. The brilliant light causes us to squint and perhaps turn our heads away from the light - and the area it is meant to illuminate. The light scattered with the eye and lenses. Our iris, or pupil, closes down reducing the amount of light that enters our eye. The light source itself hinders a person's ability to see details not directly illuminated by the light. This degrades safety and security. One should see the hazards, not the light source.

Our natural ability to see in the dark is compromised. Our natural dark adaptation cannot occur. Thus, we will not be able to see into the less lighted areas. They will appear black. The affect on stargazers is to make the sky appear as though there are no stars!

Glare is also especially debilitating for adults over 40 years of age. As our eyes age, our pupils cannot open as large as they did in our youth. We become more dependant on the light that passes through the centre of our lenses. Unfortunately, this area is where cataracts begin to grow. Thus senior citizens find it increasingly difficult to see well. For them, more light actually reduces visibility. The short wavelength light that make sup "white light", most easily scattered where as the longer wavelength light of yellow and amber has less effect.

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 and should not shine across neighbouring properties. Neighbours have arguments about lights left on all night that shine across the property of others. A simple shield on the offending light can solve the problem (see below).

We could also question the use of these all-night lights. If the owners have gone to bed, the only use for the light is to help vandals and others see their targets. A waving flashlight in the middle of the night is more suspicious than a constant floodlight.

A badly lighted commercial property adjacent to a residential area can lower the value of the homes because of the flood lighting that overwhelms the more subdued and tasteful lighting of a suburb.

Sky Glow is produced by two phenomena - one natural and one that is artificial. Natural sky glow is produced at night by emissions from gases high in our atmosphere. We can't do anything about this, but then it is so faint that most people never notice it.

However, artificial sky glow dominates urban areas. It is caused by light that scatters off dust and large air molecules around a city. It creates a dome of light that can be seen for hundreds of kilometres. This light was intended to illuminate the ground but, due to poor design, it is misdirected upward into the sky. It wastes energy and it obliterates the view of the natural night sky.

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