Light pollution is caused in part by the use of poorly designed or misapplied outdoor "light fixtures", which in lighting parlance, are luminaires. Many people have the misconception that "bright lights" provide the best lighting at night. If you can see the direct glare from a light fixture, visibility is being compromised. Most people don't give much thought to the various types of outdoor lighting in their community, until it becomes a problem for them. Next time you are out at night, take a look at how roads, parking lots, buildings and signs are illuminated.
What you will see are examples of good outdoor lighting fixtures that illuminate their targets such as roads, parking areas, and sidewalks, without casting dazzling glare into your eyes. These fixtures are of the "shielded" type. Shielded fixtures do not emit any direct uplight. You will also be likely to see examples of bad lighting fixtures that are of the "unshielded" type. Such fixtures emit hazardous glare that hampers the vision of motorists and pedestrians. They also cause light trespass onto neighboring properties and into home windows. Unshielded light fixtures waste energy by spilling their light into the sky, causing a murky skyglow that keeps us from viewing the natural night sky. Direct uplight is scattered by air molecules, moisture, and airborne dust and fibers, creating a general sky glow around populated areas that can interfere with the breeding and feeding habits of nocturnal animals.