What is Light Pollution?
Light pollution is the excessive use of light at night. It can have many negative effects on migratory birds, insects, energy consumption, and even human health. Artificial light affects animals’, amphibians’, and mammals’ normal nocturnal activity, which in turn can affect the population.
The image above shows light pollution’s effect on sky visibility at night. The sky is evaluated on the Bortle Scale—a nine-level numerical scale that measures the sky’s brightness due to light pollution. The sky gets progressively darker from left to right as the image goes from the inner city to an excellent dark sky site.
- 9 – Inner City Sky: The sky is very bright with only a few objects like the moon, planets, bright satellites, and a few bright stars visible.
- 7 – Suburban/Urban Transition: Light pollution makes the sky look light grey and even with a telescope stars are dimmer than they should be. Most of Boise is categorized as a 7 on the Bortle Scale.
- 5 – Urban Sky: Light pollution is visible in most directions, the Milky Way is invisible near the horizon and is washed out directly overhead.
- 3 – Rural Sky: Only some light pollution is visible on the horizon, many stars and some messier objects, such as M15, M4, M5, and M22, are visible.
- 1- Excellent Dark Sky Site: Very dark sky with bright and faint stars visible, the Milky Way is visible and structured.
Impacts of Light Pollution
Many animals in Idaho are nocturnal, including but not limited to: coyotes, badgers, foxes, muskrats, mice, owls, and bats. While some insects are attracted to light, studies have shown that nocturnal prey animals avoid areas with increased artificial lighting, seemingly to avoid predators. Because of this, increased artificial light at night can disrupt predator prey relationships.
Street lights have also been shown to affect migration and reproduction timing in Salmon. Juvenile Salmon tend to migrate at night and since Salmon are attracted to light, they will stop at light sources rather than continuing their migration. Hormonal responses in many fish species are sensitive to light which in turn affects their reproduction and population in general.
How You Can Help
To limit the negative effects of light pollution and preserve our night skies we can:
- Follow Dark Sky outdoor lighting guidelines
- Ensure that light is pointed down at its target area
- Use amber or warm-colored light to help with night vision since human eyes are most sensitive to blue and white light.
- Use timed or motion-activated lights
- Turn off lights when not in use
- 1 – Useful: Use light only if needed. All light should have a clear purpose. Consider how the use of light will impact the area, including wildlife and their habitats.
- 2 – Targeted: Direct light so it falls only where it is needed. Use shielding and careful aiming to target the direction of the light beam so that it points downward and does not spill beyond where it is needed.
- 3 – Low Level: Light should be no brighter than necessary. Use the lowest light level required. Be mindful of surface conditions, as some surfaces may reflect more light into the night sky than intended.
- 4 – Controlled: Use light only when it is needed. Use controls such as timers or motion detectors to ensure that light is available when it is needed, dimmed when possible, and turned off when not needed.
- 5 – Warm-colored: Use warmer color lights where possible. Limit the amount of shorter wavelength (blue-violet) light to the least amount needed.
Dark Sky Parks
Bruneau Dunes State Park was designated as an International Dark Sky Park in June of 2024. To adhere to dark sky guidelines, the park has upgraded all outdoor park lighting to dark sky-friendly fixtures and continues to incorporate dark sky messaging into its educational programming in and out of the park.
Want to learn more about light pollution and discover other Dark Sky Parks? Visit the Dark Sky International website!