The Problems of Light Pollution -- Overview
Light pollution: Any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste. Light pollution is not only a hinderance to astronomy, but it also impacts us directly.
Light pollution:
is a risk factor for cancer to people
is a disturbance to animals
is a waste of energy, resources, and money
is a security risk to your property
and obscures our view of the wondrous night sky.
Urban sky glow - the brightening of the night sky over inhabited areas. It is the "glow" effect that can be seen over distant populated areas. This light that escapes up into the sky is created by the combination of all light reflected off of what is being illuminated, from all of the badly directed light in that area, and from that light that is scattered (redirected) by the atmosphere itself from reaching the ground. This scattering is very strongly related to the wavelength of the light when the air is very clear (with very little aerosols). Rayleigh scattering dominates in such clear air, making the sky appear blue in the daytime.
http://cescos.fau.edu/observatory/lightpol.html
