We usually see light in a positive light. But nocturnally migrating birds beg to differ — and so do birders, scientists, environmentalists and stargazers.
Light is a genuinely harmful form of pollution, according to the International Dark-Sky Association, also known as IDA. Eighty percent of the world’s population — and an incredible 99 percent of Americans — live under an artificially glowing sky that blocks some, most or even all the stars, according to IDA.
The march of technology toward better lighting is the main reason. Incandescent bulbs, invented in the mid-1800s, emit amber and yellow hues — the warm colors of sunrise and sunset — which have long wavelengths that don’t diffuse into the sky.
Incandescent bulbs aren’t major light-pollution culprits.
LED light bulbs are.
They have become common in outdoor street and advertising lamps and car headlamps. LEDs emit a broader and brighter spectrum. They emphasize intense blue-white light that has a short wavelength, diffusing easily into the sky. (That’s why the daytime sky naturally looks blue.)
If you’ve ever gazed south toward Portland at night and noticed a vague, hazy shine hovering there, what you’re seeing is called skyglow — the widespread spillover of city lights into the sky.
Birds can become confused, trapped and exhausted by skyglow. According to Audubon, an estimated 1 billion birds die annually due to direct collisions with illuminated buildings, towers and other structures in the U.S. Skyglow is also bad for other nocturnal wildlife, and for people, who tend to experience health effects such as insomnia as their biological clocks get out of synch with the day.
Here are five principles for responsible outdoor lighting from the International Dark-Sky Association:
- Useful. Is the light necessary? Does it have a clear purpose? Consider reflective paints for curbs and steps instead of outdoor lighting.
- Point downward. Stick with fully shielded light fixtures that prevent sideway leakage. Target the light carefully.
- Low intensity. How bright do you need? Don’t re-create sunshine at night. Reflected light on pavement and sidewalks is a big contributor to skyglow.
- Warm colors. Warm-white light bulbs produce an amber-yellow tone that’s easier on the eyes and less impactful to the environment than harsher, brighter blue-white lights that cause most light pollution. A color temperature of 2700 Kelvin or less is ideal.
- Control. Turn off lights when not in use. Use timers or motion sensors. “Light where you need it, when you need it, in the amount you need, and no more,” the International Dark-Sky Association advises.