Do you sometimes find yourself squinting at night just to see the roadway? Do you ever wonder why that is? Surely all the glare and obtrusive light causing this loss of visibility must be necessary-part of civilization.
After researching the causes of light pollution, we realized that we can have effective outdoor lighting without these problems. As a result, adopting a comprehensive outdoor lighting ordinance whose goals are to reduce unnecessary glare, thereby improving night-time visibility for safety and security. The ordinance will also help reduce unnecessary sky glow. Most of these improvements will even save energy, as well as reduce cost.
ENERGY SAVINGS
Much of the outdoor lighting that we see at night wastes energy in the following different ways: by excessive illumination, by unshielded or misaligned light fixtures, and by inefficient lamp sources.
EXCESSIVE ILLUMINATION.
The Illuminating Engineering Society of North America (IES) publishes recommendations for the lighting industry that include illuminance levels for outdoor lighting. We think these recommendations are safe and adequate and generally need not be exceeded. Increasing these levels is usually a waste of energy, since our eyes quickly adjust and the brightness often appears to be about the same.
Another waste of energy is when parking lots are brightly saturated with light after closing hours. Recommendations are towards reducing lighting levels "to maintain security when there is a low level of nighttime activity". This can easily be accomplished by leaving lights on near building entrances or other crucial places and to shut off most or all the rest.
UNSHIELDED OR MISALIGNED LIGHT FIXTURES.
Shielded light fixtures are generally referred to as "cutoff". When non-cutoff fixtures are used, glare is usually present within a driver's field of view. Luminance is the light we see reflected off the roadway surface or object being observed. When glare is visible, the IES states "stray light within the eye produces a veiling luminance...thereby impairing the ability of the driver to perform visual tasks". Utilizing full cutoff light fixtures significantly reduces glare and the "veiling luminance" effect, thus improving visibility.
Floodlight type of light fixtures, when misaligned or without appropriate visors, can contribute heavily to light pollution. Wall-pack flood lights can't be adjusted for directional control and are a poor choice for almost any outdoor lighting use. When improperly installed on buildings or poles, floodlights may even send more light upward and sideways than within the intended target areas.
The criterion for designing outdoor lighting has mainly been illuminance (the light that reaches the surface of the roadway or parking lot). However, the IES states "The human eye cannot see the light that strikes the pavement. It can only react to the pattern of light that is reflected in its direction". When glare is present, the veiling luminance effect "kicks in", blocking our ability to see all of this light. We do, in a sense, waste energy to produce light that we can't see because of glare. Even discomfort glare, a lesser kind of glare, should be avoided when possible. The IES says "discomfort glare may cause fatigue which may result in driver error".
INEFFICIENT LAMP SOURCE.
Use of the best lamp for the lighting task is crucial for maximizing energy efficiency. For example, if metal halide lamps were chosen over high pressure sodium (HPS) lamps to illuminate a parking lot it could cost 30-50 percent more in energy use than is necessary. If mercury vapor lamps were selected over HPS, the additional energy required could be 150 percent greater.
COST SAVINGS
Well designed outdoor lighting systems utilizing shielded luminaires should not cost more than poorly designed systems. In fact, reducing light pollution could even save money. The International Dark Sky Association (IDA), an organization that has been leading the anti-light pollution movement, estimates that over a billion dollars is wasted each year in unnecessary energy use.
The answer is not more light but the right kind of light. Cities and towns have never been more brightly lit, yet there is more crime than ever before. To a great extent, the attitude toward outdoor lighting today is like that of the auto industry during the gas-guzzling days of the sixties and seventies. If some light is good, then more must be better.
We're being blitzed with advertising for home security lighting by discount and home improvement retailers. Some of these light fixtures are energy efficient, but most are not. Some have directional control capability, but most do not. Glaring bright security light from dusk to dawn create a blinding illusion of home protection, but intruders can often hide in the harsh shadows from this glare. Being safe and feeling safe are not the same.
