There are a number of laws and regulations concerning the lighting of roadways and intersections at night so that drivers, pedestrians and bicyclists using the road at night, can see and be seen. These laws vary from state to state and country to country, but there are some general laws which apply to street and decorative street lighting.
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There are specific lighting fixtures which are allowed over roads, to keep as little light pollution from occurring as possible. All roadway lights must only shed light in the 180 degrees below it, pointing straight down. The full cut off fixture is certified by the manufacturers to not allow light to be emitted above it and reduces glare by limiting the light to less then ten per cent at ten degrees below the horizontal. Shields can also be added to these street lamps to direct the light below it, so that it doesn't shine into anyone's property.
Spacing of Poles
Street lights on poles over modern, busy roadways are important and based on the lighting fixtures each of these street lamps use. The distance between lights should be based on where the glow of one street light ends. This distance should be doubled and that is where the next street lamp should be installed, with the street light at the same height. This type of lighting and pole spacing is best used on major thoroughfares or highways in a metropolitan area. This much street lighting is not needed for rural areas, and usually municipalities cannot afford it.
Voltage of Lights
Street lights should not be over 250 volts. Lights which are any brighter will cause too much light pollution as the light reflects off the ground and also distracts residents who have a home near the street where these brighter street lamps may be placed. This is standard for most suburban or residential streets. In some industrial areas or highways where more light may be needed, 650 volt street lights are employed to properly light the street. These lights are not to exceed 3000 volts.
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