Clear Skies Ahead

Mar 8, 2019
Clear Skies Ahead

Careful design solutions can ensure that birds maintain a view of the stars during migration

By Jane Slade

It is estimated that the world population will surpass 11 billion people by 2100. Not only must wildlife contend with the human footprint and a fight for resources, there is also the intangible necessity of darkness that is slowly being encroached upon through modern lighting practices. With every person born, more unnatural light will be shone upon wildlife.

The natural cycle of darkness is part of a complex language for all organisms on Earth, regulating circadian rhythms and key aspects of survival such as reproduction and feeding habits. For each species, a lack of darkness causes unique issues that threaten survival, impacting not only individual organisms, but relationships both within and between species.

For birds in particular, a clear view of the stars is vital for migration. Light from buildings not only reduces visibility of the night’s sky, but also distracts birds along their migratory routes. It is estimated that up to 1 billion birds fatally crash into buildings in North America each year. For some species, this loss in population is “biologically significant.”1

According to the Model Lighting Ordinance—a document jointly created by the IES and the International Dark-Sky Association offering model lighting regulations for communities—one light fixture has the ability to create light pollution up to 120 miles away.2 If it only takes one fixture to disrupt darkness, we must approach lighting with regards to wildlife with extreme caution.

Early Adopter

The city of Flagstaff, AZ, was one of the earliest advocates for the preservation of dark skies, passing its first lighting ordinance over 60 years ago, in 1958. In 2001, Flagstaff was named the world’s first Dark Sky Place, achieving light emissions around 14 times dimmer in comparison to other cities of similar size such as Cheyenne, WY.3

Flagstaff reduced impact upon birds by maintaining a clear view of the stars through careful design choices. Counterintuitively, the city decided to hang back from the technological advances of LEDs, instead keeping with low-pressure and high-pressure sodium sources, as the limited bandwidth of the yellowish light reduces the impact of light pollution on the night’s sky. Additionally, it has been shown in some cases that sodium-vapor sources have less of a circadian stimulus on wildlife than broad spectrum light.

In fact, specific wavelengths of light may actually increase light’s impact upon certain species. For birds, sources with high spectral power density in red wavelengths have been shown to be particularly impactful. In one study, red light stimulated the reproductive system of poultry, increasing the number of eggs produced.4 In another study, red light disrupted magnetoreception and orientation for migratory birds.5 One such theory is that this light simulates the onset of springtime. For other animals and plants, stimulating wavelengths may vary in color greatly. In the future, light sources may be designed to have combinations of wavelengths to best reduce impact on specific ecosystems and species.

What’s Being Done

Bird safety is an important design parameter for cities such as San Francisco. In fact, the Planning Department of San Francisco published an entire document on bird safety, citing the importance of lighting design and architecture to support bird migration.6 Located in the middle of the Pacific Flyway, San Francisco is a midpoint for millions of birds migrating along spectacularly long journeys, stretching as far as Patagonia to Alaska.

For this reason, the city recommends designing buildings with bird safety details, especially regarding tricky materials such as glass. While it passively allows daylight to illuminate interiors (and solar heat gain for another matter), it can also serve to attract birds, who do not perceive form in the reflective surface but rather a void. It is recommended that glass be frosted, fritted, or even angled in such a way as to create a readable surface, and that overhangs are utilized over windows so that birds can better perceive a building in space.

Design solutions can also treat buildings after-the-fact, when particular window exposures are found to be repeat offenders in attracting birds off course. Solutions can range from the use of lighting controls, installing blinds, adding screens that attach to the outside of the building, or even perhaps innovations that have yet to be invented.

Landscape architecture also can be used as a tool to augment lighting designs for the safety of birdlife. Through strategic planting of native flora, birds can be drawn to safe habitats along migratory routes, bypassing buildings altogether. It has been shown that large window exposures overlooking open spaces with vegetation increase bird collision significantly. 7 Plants can be used on the outside of window exposures to help birds recognize glass surfaces. Conveniently, most innovations with regards to landscape architecture provide multiple benefits for sustainability.

An important next step in lighting design will be to find consensus in acceptable lighting levels for both humans and wildlife, including a low tolerance for upward light of any kind. We are at the onset of light addiction, with LEDs so small they can be put almost anywhere, making once acceptably bright places seem dark again in contrast. While the Model Lighting Ordinance serves as a starting point, it is necessary to continue developing a cohesive model for lighting. As LEDs proliferate, lighting regulation must be developed simultaneously.

The design innovations above are just the beginning of integrating the needs of birdlife into lighting design. Moreover, the future of lighting design must aspire to model the natural daylight cycle as closely as possible, to best support all living things on Earth. Sustainable lighting design is not a choice or a benefit, but an absolute need. Through creative thinking, there are boundless solutions to illumination that consider the welfare of both humans and wildlife.