Roadside billboards are prime examples of this kind of waste since most of their light simply shines into the sky rather than illuminating the sign. Compare the skies above a billboard lighted from the bottom compared to one lighted from above, you'll see a dramatic difference. Specific light pollution problems range from annoying to life threatening. One is called light trespass, where light from one property spills onto another. This leads to strife between neighbors and leads residential neighborhoods to oppose nearby commercial development which will blanket their homes with annoying light.
Glare is the most dangerous of light pollution problems.
It comes from seeing either the bright lamp itself or a low angle reflection, both situations caused by improperly shielded lamp fixtures. Glare has been shown to be the cause of MANY automobile and industrial accidents and deaths, especially under conditions like wet roadways or highly reflective floors.