Light pollution is the intrusion of unwanted or unneeded artificial light into a man-made or natural environment. A variety of somewhat separate phenomena comprise the overall issue of pollution due to excess artificial light: Over-illumination, glare, light trespass and skyglow. Adverse impacts of light pollution include human annoyance, interference with ecosystems, human health effects, interference with astronomical observation and wasteful consumption of energy. Sources of interior light pollution consist chiefly of unnecessarily intense lighting; principal sources of outdoor light pollution include street lighting, poorly designed stadium and recreational lighting, gratuitous building uplighting and unnecessary use of office interior lighting intruding into the night sky.
Local governments have begun to regulate certain aspects of light pollution; in particular, numerous municipalities have established standards that control the amount of light traversing property boundaries. Regarding exterior lighting fixtures and skyglow issues, some governmental agencies and lighting manufacturers have established standards that limit the quantity of light that is wasted by emanating skyward and not illuminating the ground target.