Light pollution is an interesting occurence caused by the sheer idiocy of humans. Granted, there is one natural source of light pollution, but the vast majority is man-made. Poor ambient lighting is the main cause of this; it can come from lights for security on buildings, halogen lights, search lights, whatever. Indeed, it can pose a serious threat to drivers on the road as overlighting can lead to glare and decreased visibility - which, ironically, lights are supposed to improve.
It is the worst in populated areas; lack of any sort of light pollution ordinances has led to the reddish haze that enth describes. Most people just ignore it - after all, who looks at the sky anymore?
The most agonizing thing about this whole issue is that it's relatively simple to fix. A gas station, for example, can use recessed lighting in its canopy where the refilling stations are. Most gas stations use protruding lights, which serve absolutely no purpose but to throw glare everywhere and waste electricity.. Businesses which need security lights can use properly shaded sodium lamps. Bright lights are horrible for security reasons because they create a sharp contrast between light and dark, allowing a potential intruder to slip by unnoticed in the shadows.
Another very irritating source of light pollution are old-style or light orb street lamps. Light orb street lamps throw light everywhere except under the street lamp. A striking example of this blatant waste of electricity is present right in my hometown. The city's light rail provider has several park-and-ride parking lots which are illuminated by no less than 50 light orb lamps - at all nine parking lots along the light rail route, making them very highly visible from far off. Next to the parking lot is a U-Haul store, which is about the same size as the parking lot, and for some strange reason the parking lot outside the U-Haul store has better lighting, with fewer lights - they use SHIELDED lights!.
Crimes are very rarely committed in the sky. Why are we shining all that light up there?