Go Green: Light pollution disrupts plant, animal and human rhythms

A child of the suburbs, I was 40 before I saw the Milky Way, our home galaxy.

Lying on my back on a prairie hilltop near Manhattan gave me a long overdue sense of my size and place in the larger universe, a sense my ancestors, living in a much darker world, had taken for granted.

Because of light pollution, more than two-thirds of the world’s people cannot see the Milky Way. Views of the night sky aren’t the only casualties of light pollution.

Vegetation of all kinds, including fruit trees and gardens, suffer ill effects of continuous light. It inhibits a plant’s ability to form and maintain chlorophyll in its leaves. Chlorophyll is the substance made by plants that turns leaves green and allows the plant to convert nutrients into food. Light pollution also interferes with plant flowering and promotes leggy growth.

Light pollution also disrupts the lives of animals, sometimes fatally so. It disrupts feeding and breeding activities in nocturnal animals — half of the world’s species — including birds, bats, frogs, salamanders, fish, fireflies and zooplankton. It alters their circadian rhythms, changing the balance in predator-prey relationships and causing sometimes-fatal hormonal imbalances.

Migratory birds are at particular risk in light-polluted areas. Birds navigate by the stars, and the relatively recent intrusion of artificial light from cities can confuse them. During a storm event, birds can drop below the cloud deck looking for visual or magnetic clues from the night sky. Many die from collisions with windows. Others, already tired from their migratory journeys, hover in the moisture halo around artificial lights like moths and drop dead from exhaustion or are taken by predators.

Like our animal relatives, we humans suffer from light pollution as well. Disrupted circadian rhythms suppress melatonin production. Reduced levels of this beneficial tumor-suppressing hormone can result in increased risk of breast and other cancers.

Excessive lighting can also lead to conflicts between neighbors. When Lisa and I first bought our house, we left our back porch lights on all the time in a misguided attempt to keep ourselves and our property safe.

With exquisite tact, our neighbor across the alley asked us if we could turn off or redirect the lights since one of them beamed directly into his ill mother’s bedroom, keeping her awake. In a very real way, we had been trespassing. A couple of hundred dollars later, we had installed motion-detecting lights and beamed them toward the ground where the light belonged.

It’s a good idea for homeowners to check their property line after dark to see if they are intruding on another person’s right to darkness. If in doubt, ask your neighbor.

Reducing outdoor lighting will also cut down your carbon footprint and energy bills.

Following are some outdoor lighting tips:

  • Direct light toward the ground by choosing the right fixture.
  • Turn off lights when not in use.
  • Select the correct bulb and wattage.
  • Use sensors, timers, and motion detectors.
  • Limit fixture height.
  • Use full cut off or fully shielded light fixtures, which direct light downward.

For more tips about reducing light pollution, visit darkskysociety.org.