Light Pollution

Light pollution is the introduction of artificial light into the outdoor

environment. Its impacts are many. Light pollution disrupts natural

diurnal patterns of light and dark and the rhythms of life to which

plants, animals, and humans have adapted, interrupting circadian

sleep cycles, interfering with normal plant growth and disturbing the

habitat of nocturnal wildlife.

Light pollution interferes with the ability to view and observe the

the night sky, stars, and planets. It causes light trespass, which is the

nuisance spillage of light from one property onto another, risking

the conflict between neighbors. It can cause safety hazards, such as

glare and temporary blindness, for drivers. Light pollution wastes

energy, causing associated adverse environmental and economic

impacts.

Night lighting for surveillance can actually increase security risks.

Although exterior lighting can create a perception of safety, research

has shown that night lighting might not lower crime levels. Lights

left on all night provide no signal of illegal activity, whereas lighting

turned on by motion sensors can serve as just such a signal, and can

possibly deter intruders. Exterior lights can also cause glare in some

areas and shadows in others, which can mask intruder access.

Strategies to reduce or eliminate light pollution include selecting

light fixtures that minimize spillage and focus light downward rather

than outward and upward into the sky. A variety of other design

choices can also reduce light pollution, such as specifying pathway

lighting instead of higher pole-mounted area lighting; using pole mounted

lighting instead of wall-mounted lighting; locating outdoor

amenities, such as parking and outbuildings, closer together and

nearer to the main buildings they serve; designing lower levels of

lighting and eliminating up lighting; and specifying such controls

as motion sensors that keep exterior lights off most of the time.

Installation strategies include aiming light fixtures downward and

commissioning outdoor lighting controls, such as delay settings for

motion sensors and timer schedules. Another option is to eliminate

exterior lighting wherever possible.

A related issue is spillage of light from the indoors to the outdoors.

Solutions to this problem include installing lighting controls to turn

lights off when not needed at night; reducing light levels indoors

during late-night hours; eliminating windows in spaces not requiring

them, such as stairwells and utility areas; reducing window size in

areas where larger windows are not needed; adjusting the relative

location of lights and windows; reducing lighting near windows,

shielding light fixtures, and avoiding orienting lights toward the

outdoors.