When outdoor light is wasted by going where it is not useful, such as up to the sky, it is forever lost. Valuable oil is consumed. Precious natural gas is burned up. Coal is wasted.
Hydorelectric energy is lost.
Glare confuses and blinds our eyes. Light trespass offends neighbors. Safety hazards are created by glare and bad contrast levels. The beautiful night sky disappears. Full cutoff fixtures put light where it belongs, on the ground.