Light pollution is excessive or misdirected artificial light. It brightens the night sky, washes out stars, and disrupts ecosystems. City dwellers often see only a handful of stars. In truly dark places, thousands are visible. The difference is light pollution.

It comes in several forms. Skyglow is the bright halo over cities. Glare is harsh light that hurts the eyes. Light trespass is light spilling where it is not wanted. Clutter is confusing groups of bright signs. Each has different causes and fixes.

Wildlife suffers. Sea turtle hatchlings crawl toward artificial lights instead of the ocean. Migrating birds collide with illuminated buildings. Insects swarm around streetlights and die of exhaustion. Nocturnal animals lose feeding and mating cues. Human health may also suffer. Artificial light at night disrupts sleep and circadian rhythms. Solutions are simple: shields, timers, motion sensors, and warmer colors. The night sky returns when we stop wasting light.

Common sources

• Streetlights
• Advertising signs
• Building exterior lighting
• Parking lot lights
• Residential security lights