Limited Outdoor Lighting

Image credits: Koushalya Karthikeyan, Unsplash

Limited outdoor lighting can mitigate the negative impact of lighting on wildlife and human health. Practices limiting the amount, intensity, and high color temperature of lighting can have positive impacts on wildlife and humans.

Biodiversity role:

Limiting artificial light at night mitigates negative impacts on wildlife communication, orientation, reproduction timing, predation, habitat selection, circadian rhythm, plant phenology, and ecosystem services.

Human health role:

Artificial lighting is linked to increased breast and prostate cancer risk, increased cortisol, increased vector borne disease risk, and disruptions to circadian rhythm and melatonin production. Disruptions to circadian rhythm are associated with negative impacts to psychological, cardiovascular, and metabolic functions. Limiting light mitigates these impacts.

Key tensions and tradeoffs:

While reduced lighting itself may not lead to increased crime, it is tied to reductions in perceived safety, which is important for equitable use of public space. Outdoor lighting has been linked to physical activity in parks and is important for utilization of a space after dark. Lighting can direct users to well-lit high-use greenspace areas, while limiting use of areas kept dark for habitat.

Limit amount of lighting

The most effective way to lower the impact of artificial lighting is to reduce the amount of overall light. Lighting can be limited to high use areas, leaving greenspace for habitat unlit. Lighting timers, motion sensors, or lighting curfews can be used to limit lighting to high use times.

Reduce light trespass

Many light fixtures cause light to shine into areas where it is not needed, such as the sky or sensitive habitat, which negatively impacts wildlife and humans. The backlight, uplight and glare (BUG) system developed by the International Dark-Sky Association can be used to choose low BUG rating fixtures.

Limit lighting intensity

Lower the intensity of artificial lighting to reduce the impact. Intensity of lighting has been tied to breast cancer risk and melatonin suppression. Setting a maximum illuminance of 1-3 lux in sensitive habitat areas can reduce impact to species, while providing enough light for people to see.

Avoid blue-white light

While species differ on the colors of light they are most sensitive to, broad spectrum blue lighting (>3000K) is the most harmful to both wildlife and human health. Using narrow spectrum lighting, with warmer color temperatures, such as under 2700K, can reduce impacts to wildlife and health.

Consider target species

Impacts of specific lighting practices differ by species. While reducing the overall amount of lighting in an area will have the broadest benefits, certain interventions may be more beneficial to a species of concern. For instance, yellow low pressure sodium lighting can be used to mitigate impacts to sea turtles.

Use lighting based on site context

A wetland area along a suburban greenway will have different lighting needs than a green street within the urban core. The Model Lighting Ordinance (MLO) developed by the International Dark Sky Association uses lighting zones to provide lighting guidance based on site context.

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