A For most of human history the night sky was a shared view. Today, in many cities, artificial light is so bright that only a handful of stars can be seen, and many children have never seen the Milky Way. Light pollution, as this brightening of the night is called, has been increasing in many regions for decades as street lighting, advertising and buildings have become brighter.
B Wildlife is affected in several ways. Many migrating birds travel at night and can be drawn off course by lit towers, and large numbers die from collisions or exhaustion. Newly hatched sea turtles move towards the brightest horizon, which should be the sea, but on lit coasts they may head inland. Insects gather around lamps and are easily caught by predators, which can disturb food chains.
C Researchers are also studying the effect of light on people. The body clock responds to light and dark, and bright light in the evening can make it harder to fall asleep. Some studies link night-time light to poorer sleep, but the evidence for effects on long-term health is still developing and scientists are cautious about making firm claims.
D Fortunately, solutions are inexpensive. Lamps can be shielded so that light shines down, not up into the sky. Warmer coloured bulbs disturb wildlife less than very white ones, and dimming or switching off lights late at night saves energy. Some regions have created dark sky reserves, where lighting is controlled so that visitors can enjoy the stars.
