Turn off outdoor lights at night

Why it matters

For most of evolutionary history, the only light at night came from the moon and stars. The insects, bats, and birds that evolved in that darkness built their navigation, foraging, and migration systems around it. Artificial light at night disrupts all three.

Research published in Ecology and Evolution found that artificial light at night affects nocturnal insects across five distinct categories: disorientation, changes in predator-prey dynamics, disrupted reproduction, altered foraging patterns, and interference with bioluminescent communication. Light pollution is expanding globally at 2 to 6 percent per year, and insect abundance has declined dramatically over the same period.

Bats are directly impacted too. Many bat species avoid lit areas entirely, which reduces their foraging range and fragments the dark corridors they rely on to move through the landscape. Studies show that bat activity increases when artificial light sources are switched off at migration sites.

For birds, the effects are equally serious. Research published in Nature Communications identified artificial light at night as one of the strongest predictors of bird migration stopover density across the United States, suggesting that lit urban and suburban areas act as ecological traps that concentrate and disorient birds during migration. Billions of nocturnal migrants cross North America twice each year, and many navigate using stars and the earth's magnetic field. Both are disrupted by artificial light.

How to do it

1. 1Turn off lights you don't need: start with any outdoor lights that run all night without a purpose. Decorative garden lighting, always-on porch lights, and uplighting on trees are the easiest to switch off completely.
2. 2Switch to motion sensors: replace always-on security lights with motion-activated versions. They provide the same security function while restoring darkness between activations. Most motion sensors can replace existing fittings in under 30 minutes.
3. 3Use timers: for lights that need to stay on for part of the evening, set a timer to switch them off. Most insects, bats, and migrating birds are most active in the first few hours after dark.
4. 4Choose warmer or amber bulbs: if you can't remove a light entirely, switch to a warm white or amber LED. Research shows that shorter-wavelength blue and white light is significantly more disruptive to insects than longer-wavelength amber light.
5. 5Shield and direct light downward: use shielded fittings that direct light downward onto the ground rather than outward and upward. This reduces skyglow and limits the radius of disruption for flying insects and bats.