Dark Sky Lighting – The Hows and Whys of Dark Sky Lighting

Preserving Night Skies and Enhancing Safety

Dark sky lighting involves the use of outdoor light fixtures specifically designed to minimize light pollution. These fixtures typically feature shielded LEDs with low Kelvin ratings, which direct light downward instead of allowing it to scatter across the sky and ground. This targeted lighting approach helps preserve the natural darkness of night environments while still providing adequate illumination for safety and security.

The benefits of implementing dark sky lighting standards are multifaceted. For astronomers, it enhances the clarity of the night sky, making celestial observations clearer and reducing the interference that light pollution causes. Ecologically, it supports wildlife habitats by maintaining the natural patterns of light and dark that many species rely on for survival. For humans, it reduces glare, which improves safety by increasing visibility and enhances the overall quality of life by restoring the natural nocturnal environment.

Internationally, the movement towards dark sky compliance has gained momentum. The establishment of dark sky communities and dark sky parks, both in the USA and around the world, highlights a growing commitment to sustainable and responsible lighting practices. These areas are dedicated to preserving the natural night environment through community-wide lighting policies and public education on the importance of reducing light pollution.

What Is Dark Sky Lighting?

Dark Sky Lighting encompasses a range of outdoor lighting fixtures and practices specifically crafted to reduce light pollution and its adverse effects on the environment, wildlife, and human health. This type of lighting is a crucial component in efforts to mitigate the negative impacts of artificial light that radiates into the night sky and disrupts ecosystems.

Dark sky compliant fixtures are meticulously engineered to ensure that light is directed downwards rather than upwards or outwards where it can contribute to skyglow. This directional lighting is key in preventing the scattering of unnecessary light into the atmosphere, which obscures our view of the stars and interferes with astronomical research.

These fixtures typically incorporate full cutoff designs that eliminate excess illumination. This design is vital as it confines the beam of light to the needed area—such as walkways, streets, or public spaces—enhancing visibility and safety without waste. By implementing fixtures with proper shielding, dark sky lighting also prevents light from trespassing into unwanted areas, such as residential windows, which can be a source of nuisance to inhabitants.

Moreover, the choice of color temperature in dark sky lighting plays a significant role. Cooler temperatures, which produce a blue-white light, are more likely to contribute to light pollution than warmer temperatures. Thus, dark sky standards recommend using lights with a color temperature of 3000 Kelvin or lower, which is gentler on the eyes and less disruptive to nocturnal wildlife. The appropriate brightness levels are also critical; overly bright lights can cause glare and are counterproductive. Properly calibrated brightness ensures adequate visibility without overpowering the natural darkness.

Light Pollution and Its Effects

Light pollution is the excessive and inappropriate use of artificial light, which has harmful consequences on the environment and human health. Effects of light pollution include:

• Disruptions to ecosystems: Artificial light at night can disrupt the natural behaviors and biological cycles of wildlife, affecting their feeding, mating, and migration patterns.
• Human health: Exposure to excessive lighting at night has been linked to sleep disorders, obesity, and even an increased risk of cancer.
• Energy waste: Unnecessary lighting contributes to energy waste and increases greenhouse gas emissions.
• Loss of night sky visibility: Light pollution affects our ability to view the night sky, making it difficult to observe stars, constellations, and other celestial phenomena.

To address these issues, organizations such as the International Dark Sky Association (IDA), now known as DarkSky, are dedicated to advocating for dark sky-friendly lighting and policies.

DarkSky, established in 1988, is a dedicated non-profit organization focused on the preservation of night skies through the reduction of light pollution. This is crucial not only for the beauty of natural landscapes but also for ecological health and human well-being. Here’s an elaboration on their main initiatives and their practical impact:

Certifications

DarkSky awards certifications to parks, reserves, and communities that actively work to preserve the night sky. To earn certification, these places must implement strict lighting regulations and engage in active public outreach. This not only helps in maintaining dark skies but also promotes community involvement and awareness about the importance of natural night environments.

Guidelines

The organization devises detailed guidelines and standards for outdoor lighting that help minimize light pollution. These guidelines are aimed at industries, residential areas, and public spaces to encourage the use of lighting that does not disrupt the natural night environment. By promoting lighting that is less intrusive and more directed, they help reduce the spread of unnecessary artificial light.

Education and Outreach

DarkSky’s efforts to educate the public and policymakers about the adverse effects of light pollution form a core part of their mission. They use educational materials, organize public events, and form partnerships with other organizations to spread knowledge about how light pollution affects not only our view of the stars but also the natural behaviors of wildlife and our own health.

A tangible example of DarkSky’s principles in action is the project undertaken by the Appalachian Mountain Club in collaboration with the town of Greenville, Maine. This project exemplifies how DarkSky’s ideals can be implemented practically. The Appalachian Mountain Club helped the town obtain a grant and collaborated with Access Fixtures to design and manufacture outdoor lighting that was secure, facilitated safe movement, and protected the natural night environment. The project is an example of how communities can enhance safety and security without compromising the integrity of the night sky, demonstrating the practical benefits and beauty of dark sky-compliant lighting.

Environmental and Wildlife Conservation

The reduction of artificial light at night, as advocated by dark sky initiatives, offers substantial benefits for environmental and wildlife conservation. Here’s a closer look at these advantages:

Wildlife Conservation

Artificial lighting can severely disrupt the natural behaviors of nocturnal animals. For example, excessive light can confuse migratory birds, interfere with the hunting and foraging behaviors of predators, and affect the reproductive cycles of various species. By adopting dark sky lighting principles, communities can help preserve the natural rhythms and habits of wildlife, thus supporting healthier and more stable ecosystems.

Environmental Preservation

Beyond its impact on wildlife, dark sky lighting plays a crucial role in maintaining the quality of our night skies, which is vital for astronomical observations. This reduction in light pollution not only benefits professional and amateur astronomers by providing clearer views of the cosmos but also enhances cultural and educational experiences. For many communities, especially those in or near designated dark sky areas, this can also boost tourism, as enthusiasts and travelers are drawn to the beauty of a pristine night sky.

By implementing dark sky-friendly lighting, communities can achieve a balance that benefits both the environment and human interests, fostering a deeper appreciation of our natural world and its interconnected systems.

Energy Efficiency and Cost Savings

Dark sky lighting strategies not only contribute to the preservation of the natural night environment but also promote energy efficiency, leading to significant economic and environmental benefits. Here’s how this works:

Efficient Light Design and Placement: Dark sky lighting fixtures are specifically designed to direct light downward rather than allowing it to disperse indiscriminately. This design minimizes glare and reduces light spill into areas where it’s not needed, such as the night sky or neighboring properties. By focusing light strictly where it’s required, these fixtures use energy more efficiently, which helps in reducing overall consumption.

Use of Advanced Technologies: Incorporating energy-efficient technologies like LED lights, which can be tailored to have appropriate color temperatures, enhances the effectiveness of dark sky lighting. LEDs are highly efficient compared to traditional lighting options, like incandescent or halogen bulbs, because they use less energy to produce the same or even greater light output. This technology not only ensures compliance with dark sky standards but also significantly cuts energy costs.

Economic and Environmental Impact: By reducing unnecessary light and utilizing efficient technologies, dark sky lighting decreases energy consumption, which in turn lowers electricity bills for households, businesses, and municipal entities. This reduction in energy use also means less demand on power plants and consequently lower greenhouse gas emissions, aiding in the fight against climate change.

Improved Safety and Security

The assumption that more artificial lighting equates to greater safety and security is often misguided, as research indicates that excessive or poorly designed lighting can reduce safety. Here’s a more detailed look at how dark sky lighting approaches improve safety and security:

Reducing Glare and Light Trespass: Excessive artificial lighting often causes glare, which can be blinding and reduce one’s ability to see clearly, and light trespass, where light spills into areas where it isn’t needed or wanted. Both of these issues can compromise visibility, making it difficult for residents and drivers to spot potential hazards. Dark sky lighting, designed to minimize such effects, focuses light where it’s needed without causing these visual disturbances.

Improving Nighttime Visibility: By adjusting the balance between light and darkness, dark sky lighting enhances the quality of nighttime visibility. This approach ensures that lighting is sufficient to safely illuminate areas without overpowering the natural darkness. Such balanced lighting helps people navigate spaces safely at night, clearly distinguishing potential dangers without the disorientation caused by harsh lights.

Creating Safer Environments: The strategic use of dark sky lighting contributes to creating environments where people feel secure without the drawbacks of excessive energy use and environmental impact. This is because well-designed dark sky-compliant lighting provides effective illumination for safety and security purposes while also being energy-efficient and reducing light pollution. This synergy helps maintain ecological balance, which is beneficial for both human communities and wildlife.

Full Cutoff Fixtures

Full cutoff light fixtures play a crucial role in achieving dark sky compliance, acting as a fundamental design choice for reducing light pollution and minimizing its impact on humans and wildlife. These fixtures are specifically designed to contain the light source, often LEDs, within the fixture housing. This design prevents light from escaping upwards or skyward, which is essential for avoiding light pollution that affects the night sky.

The positioning of the LEDs inside the fixture means that they are obscured from direct view. This is beneficial as it reduces the chances of the light causing discomfort or disorientation to humans and wildlife, who might otherwise be disturbed by direct exposure to bright lights. Additionally, the structure of a full cutoff fixture typically includes a lens that is positioned above the lowest part of the fixture housing. This arrangement is critical for reducing glare, a common issue with many outdoor lighting setups that can impair visibility and contribute to light pollution. By eliminating uplight, full cutoff fixtures ensure that light is directed downward where needed, enhancing visibility and safety without unnecessary waste and intrusion into the natural night environment. This strategic design makes full cutoff fixtures an effective option for environmentally conscious lighting that adheres to dark sky principles.

The images on the right show the difference between traditional wall packs and full cutoff wall packs that reduce uplight and glare.

When choosing dark sky compliant lighting, a critical factor is the color temperature of the LEDs, which is usually measured in Kelvin (K). Lower color temperatures, typically at or below 3000K, emit a warmer, softer light that is less likely to disrupt natural patterns of wildlife and is better for reducing skyglow. Conversely, higher color temperatures produce a cooler, bluer light, which can be more disruptive to ecosystems and contribute more significantly to light pollution.

For stricter adherence to dark sky principles, many communities, particularly those sensitive to ecological impacts, enforce ordinances that specify even lower Kelvin ratings. For example, it’s not uncommon to see requirements for 2700K or 2200K LEDs. These warmer tones are less intrusive to the night environment and are less likely to interfere with the visibility of the stars.

In specific applications, particularly in areas with vulnerable wildlife, the measurement may shift from Kelvin to nanometers (nm), which more precisely indicates the wavelength of light emitted. An example is in oceanfront communities in the southeast USA, where lighting ordinances often require 590nm Amber LEDs. These LEDs emit a narrow spectrum of light less likely to disorient sea turtle hatchlings, who rely on natural moonlight reflecting off the ocean to find their way to the sea after emerging from their nests. The use of full cutoff fixtures ensures that this amber light is directed downward, minimizing both skyglow and disruption to the natural behavior of the turtles. Such specific, targeted lighting measures are essential for protecting wildlife and achieving dark sky compliance. Color Temperature of Wildlife Friendly LED Lights.

The design and integration of optics are crucial in determining the performance of full cutoff light fixtures in terms of compliance with dark sky standards. Optics in lighting refer to the components of a light fixture, such as lenses or reflectors, that control the direction and spread of the light emitted from the fixture. For a fixture to maintain dark sky compliance, the optics must not extend below the housing of the light fixture. When the lens or other optical parts drop below the fixture housing, it can result in light being cast upward or outward in an undesirable manner, contributing to light pollution.

In the context of a BUG (Backlight, Uplight, and Glare) rating, which is a common standard used to evaluate the light pollution potential of outdoor lighting fixtures, a lens that drops below the housing typically leads to an insufficient rating. This is because such a configuration often allows light to escape upwards or increases glare, both of which are detrimental according to dark sky guidelines.

However, when designed correctly, optics can significantly enhance the performance of dark sky compliant fixtures. Advanced optics can precisely control the light output, ensuring that light is directed exactly where it is needed, downward and outward within the confines of the area intended to be illuminated. By using high-performance optics combined with LEDs in a full cutoff design, these fixtures efficiently focus the light, enhancing visibility and safety where required without unnecessary spillage into the sky or surrounding environments.

Shields and accessories are crucial additions that can significantly enhance the performance of dark sky compliant light fixtures by providing greater control over light distribution. Shields are particularly effective in directing the light output and minimizing unwanted light spillage onto neighboring properties. They are typically used to block light from traveling in certain directions or to partially obscure the light source within a fixture, reducing glare. Some modern shield designs are highly effective, specifically crafted to obscure only one or two LEDs, allowing for precise control over light pollution.

In addition to shields, other accessories or requirements, such as fixed arm mounts, ensure compliance with dark sky standards, depending on local lighting ordinances. Fixed arm mounts are designed to keep light fixtures in a horizontal position relative to the ground, preventing them from being tilted. This fixed positioning helps maintain optimal light direction and distribution, ensuring the light is cast where it’s needed without unnecessary spillage. When combined with the right optics, the need for adjusting the angle of the light fixture is reduced, as the light can be accurately directed from a fixed position. These features together ensure that dark sky compliant fixtures minimize their impact on the natural environment and improve the efficiency and effectiveness of outdoor lighting.

BUG Rating – Back Light, Up Light, and Glare

BUG is a measurement of back light, uplight, and glare. Some or too much of any of the three makes for poor lighting, which is typically regulated as part of dark sky compliance.  Many dark sky lighting ordinances specify the BUG rating.

• Back Light – Back light is the light emitted behind the light fixture. It is not always a consideration in dark sky lighting ordinances. For example, it would be desirable for light to be emitted 360° in a park setting for egress and safety. Back light is unacceptable on a beach where sea turtle hatchlings would be or where the light is going into the windows of housing units.
• Uplight – Uplight is the light emitted going up and that is never acceptable. Sometimes a little light reflecting up off part of the fixture, such as off a dark part of a bollard light is acceptable, but uplight off of a reflector or due to inept optics is rarely if ever acceptable.
• Glare – Glare is extreme or strong brightness in a visual field. It inhibits good vision and eliminates contrast. Glare is easy to eliminate and is never acceptable in dark sky ordinances. If a fixture is a full cutoff light fixture, chances are the glare is minimized or eliminated.

Click here information on BUG Ratings, Lighting Zones and how BUG Ratings are used. Understanding BUG Ratings

Light Trespass

While light trespass in the form of excess light going over a property line does not typically impair the visibility of the night sky, it is an inherent part of dark sky compliance. Light trespass is usually referred to and measured by light going over a property line. As it is considered both trespass and wasteful, communities with dark sky compliance ordinances typically regulate light trespass. Examples of light trespass ordinances are as follows.

• The light must be less than 1 footcandle (fc) at the property line. This regulation aims to control the intensity of light that reaches the edge of a property, thereby also indirectly controlling how much light is cast across the property as it approaches this boundary.
• The light must be less than 0.5 fc 1 foot over the property line. This stricter standard ensures minimal light intrusion beyond the property line, promoting neighborly respect and reducing waste.

These ordinances can typically be met through careful planning and the right lighting design, incorporating elements such as appropriate optics, correct wattage, optimal mounting height, and physical barriers like fences that block light at ground level. These measures ensure efficient use of light where needed while preventing unnecessary spillage into neighboring properties, aligning with the goals of dark sky compliance.

Kelvin or Nanometers

As noted earlier, dark sky compliant lighting ordinances focus significantly on the color temperature of lighting, measured in Kelvin (K), because the color temperature directly affects the impact of the lighting on both the night sky and wildlife. The general rule is that the lower the Kelvin rating, the “warmer” the light emitted, which is characterized by a more amber or red hue. Warmer light is less likely to contribute to sky glow and has a reduced impact on nocturnal wildlife, which can be disoriented or harmed by brighter, cooler light sources.

Most dark sky ordinances require lighting fixtures with a Kelvin temperature below 3000K. Within this spectrum, 2700K is often considered more acceptable as it provides a balance between sufficient brightness for safety and minimal light pollution. However, 2200K is preferred in areas where maintaining a naturally dark sky environment is a priority, such as near astronomical observatories or wildlife-sensitive locations, because, warmly, light minimizes disruption to natural patterns.

In certain cases, the ordinances might specify Kelvin and nanometers (nm), particularly for light-sensitive environments. For instance, 590nm Amber LEDs are commonly required in coastal areas to protect sea turtle hatchlings during their critical journey from nest to ocean. The 590nm wavelength does not interfere significantly with the turtles’ natural navigation cues, which are guided by the moonlight reflecting off the ocean. Some ordinances might also include a mix of 590nm and red LEDs to further reduce the ecological impact while providing adequate visibility for human use.

Other Dark Sky Lighting Ordinaces

There are many other ways that communities decide to regulate lighting. Here are a few.

• Maximum Footcandles
  • This regulation limits the maximum number of footcandles (FC) that can reach the ground. Northampton MA limits maximum fc to 5fc on most properties.
• Limit of Light Source Lumens or Light Fixture Lumens per Acre
  • This regulation limits the total quantity of light permitted to be used. For example, Flagstaff limits the total lumens per acre.
• Max – Min Ratio
  • Max/min ratio is the maximum amount of light in a given area divided by the minimum light in that given area. A typical ratio for commercial or residential egress is 10. Limiting the max/min ratio requires more points of light, less intense light, and delivers more even light.
• Light Source Visibility
  • Communities may choose to limit light source visibility from another property. While this is a form of light trespass, it is very hard to limit or control. Limiting the visibility of the light source typically requires the light sources to be kept close to the ground.
• Maximum Mounting Height
  • This is another way to limit light source visibility and keep the skies dark. It limits high mast lighting and depending on how strict the requirements are, may eliminate most if not all pole mounted lighting.