It would be difficult to imagine any community without street lights. However, selecting fixtures that promote pedestrian and vehicle safety without over-lighting the surrounding landscape can be a challenge. Most U.S. communities are committed to reducing light pollution or artificial "sky glow," the light that surrounds an urban area. Sky glow can result when light sources distribute light directly above a fixture's horizontal plane or indirectly from light that reflects upward from nearby surfaces. Advanced refractors and reflectors help meet today's "dark sky compliant" mandates by directing light exactly where it is needed. Fixtures are now classified in four categories: 1. Full cut-off. Light is not distributed at or above the fixture's horizontal plane. 2. Cut-off. A minimum amount of light is directed at a horizontal plane and light above the horizontal plane is within 2.5% of the total lamp lumens. 3. Semi cut-off. Light above the horizontal plane is less than 5% of the total lamp lumens.
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