Principles of Good Neighbor Outdoor Lighting
We all like the freedom to do as we want on our own property. However, at the same time most of realize it's also important not to intrude on our neighbor's property by our actions. We are generally careful not to projecting very loud sounds toward our neighbor, and to aim our water water sprinkler so it doesn't spray on his house, and we don't let our dog to exercise on his lawn. But often we don't stop to think that the outside lights we install on our house can also be obtrusive to our neighbors.
The fact is that the light our fixtures produce doesn't stop at our property boundary. Light travels in straight lines from our outside fixture and can directly shine on our neighbor's house and property, and then it becomes obtrusive and unwelcome. A bright, lighted, unshielded bulb on our house or yard will cause unpleasant glare in our neighbor's eyes. Glare is the uncomfortable situation in which the human eye is unable to respond both to the dark surround and also a very bright source. We instinctively squint our eyes to try to close out the offending light. If our light trespasses through the windows of our neighbor's house, and into, for example, his bedroom, then our light can even affect his ability to have a sound sleep.
The solution to prevent glare and the majority of light trespass is very simple and inexpensive. We can apply shielding to our bright outside lights, such as floodlights and other bare bulbs that are bright. "Bright" is defined In Acton's outdoor lighting bylaw as 60-120 watts for incandescent bulbs and 13-20 watts for fluorescent bulbs. Now, Acton's Outdoor Lighting Bylaw does not apply to residents of single family dwellings- so we residents are on our honor to do the right thing here! The Northeast Light Pollution Advisory Group (NELPAG) calls this Good Neighbor lighting , and we've borrowed their excellent term.
Shielding
Shielding is used to block the lamp's rays from traveling upward (causing sky glow) or sideways (and off your property). To direct the lamp's rays onto the ground- the place we are trying to illuminate after all- the shield should cover the top and sides of the lamp. A person standing horizontally to the fixture should not be able to see the lamp itself, only the glow of the light illuminating the ground. A fixture that is shielded on the top and all sides, directing light onto the ground, is called Fully Shielded. An example of a Fully Shielded fixture is shown here:
Although this fixture is most commonly used commercially (look in many parking lots in the area), the principles are the same for the smaller lights we might use on our houses. The Parabolic Reflector (PAR) lamp is the familiar cone-shaped bulb, about six inches in diameter, that is found on many houses to light driveways and yards. If unshielded, it can project light for long distances, because of the focusing reflector built into it.
Here is a picture, taken from the neighbor's lot, of an unshielded PAR light used over garage doors. The glare is obvious and unavoidable, even if the PAR light is tipped downward.
It is easy to make a simple shield using aluminum flashing and to fix it to the PAR lamp with a clamp. Cliff Haas gives directions for constructing one on his website. Installing one on these garage lights dramatically reduces glare, without much effect on the light that falls on the driveway
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You can learn much more about shielding and principles of good lighting from sites sponsored by NELPAG, Cliff Haas, and the International Dark Sky Association -we recommend all these sites to you.
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