Dealing with Light Trespass

By Chetna Misra

Light trespass—the unwelcome spill of artificial light into spaces where it’s neither needed nor desired—has become a growing concern for those who cherish the nocturnal environment. As a symptom of light pollution, light trespass not only diminishes the beauty of dark skies but also disrupts ecosystems, affects human well-being, and highlights the consequences of poorly designed lighting systems.

Understanding Light Trespass

Light trespass occurs when artificial light encroaches on areas it was not intended to illuminate. Both outdoor and indoor lighting can contribute to the problem. While outdoor lighting is often the primary focus in light pollution discussions, indoor lighting plays a significant role as well. Unshielded windows can turn homes into unintended sources of light, spilling illumination into the surrounding environment and further disrupting the natural balance of darkness, particularly in urban areas.

Key Contributors to Light Trespass

Over Lighting and Poor Design

Many problems arise from trying to do too much with one light. Attempting to illuminate large surface areas with a single fixture often leads to:

• Sky glow: The unnatural brightening of the night sky, which makes stars, the Milky Way, and other celestial features harder to see.
• Glare: Intense light that reduces visibility and comfort.
• Light trespass: Light spilling into unintended areas, impacting neighbours and the environment.

Before adding more lights to your living spaces, ask yourself: Are you truly improving things, or creating more problems?

Over lighting during the winter months is also amplified by snow, a phenomenon known as snowglow. Snow's high reflectivity, or "albedo," intensifies skyglow, brightening the night sky, especially over and around suburban areas. While snowglow primarily contributes to skyglow, it also highlights an often-overlooked aspect of light trespass. Artificial light reflecting off snow, as well as other surfaces like cement and walls, becomes an unintended source of trespassing light, spilling illumination into areas where it’s neither needed nor desired. According to Andreas Jechow and Franz Hölker in their article, "Snowglow—The Amplification of Skyglow by Snow and Clouds Can Exceed Full Moon Illuminance in Suburban Areas," snowglow can increase night sky brightness by up to 33% on clear nights, with artificial light reflecting off snow becoming twice as bright as the full moon at its peak. This emphasizes the importance of addressing not just direct lighting but also its reflective impacts to mitigate light trespass effectively.

Key Principles for Minimizing Light Trespass

Effective lighting design requires careful consideration of three key factors: shielding and blocking, mounting location and height, and brightness. Fully cut-off (FCO) fixtures are essential for directing light precisely where it is needed, minimizing unwanted spillover and glare. The placement and height of lighting fixtures are equally important, as poorly positioned lights can lead to unnecessary light trespass into neighbouring areas or the night sky. While brightness primarily affects how intrusive the light appears, managing these aspects together allows for practical, efficient illumination that reduces light trespass and preserves natural darkness without compromising functionality.

Shielding and Blocking

Proper shielding is the cornerstone of responsible lighting. In simple terms, shielding ensures that light is directed only where it is needed, reducing glare and spillover. For example, a fully cut-off (FCO) fixture has a cover that prevents light from escaping above the horizontal plane, ensuring that the light shines downward. Similarly, sharp cut-off (ShCO) fixtures provide even more precise control over the spread of light.

Practical solutions include replacing bare or globe-style fixtures with shielded alternatives, which are widely available at hardware stores. Porch lights with downward-facing designs effectively illuminate pathways and doorsteps, significantly reducing light trespass. Retrofitting older fixtures with shields is another cost-effective way to improve lighting efficiency without requiring full replacement. Motion-activated floodlights can also be valuable when aimed downward and equipped with shielding. These lights should be set to short on-times to avoid prolonged illumination, and lower brightness levels should be chosen to minimize glare and trespass.

By combining shielded designs with thoughtful practices, such as proper aiming and brightness control, homeowners can significantly reduce unwanted spillover while enhancing energy efficiency and promoting responsible illumination.

Brightness

The brightness of outdoor lighting plays a significant role in shaping how light trespass is perceived. While brightness itself doesn’t cause trespass, its intensity affects its impact—a dim garden light spilling over a property line is far less disruptive than a glaring floodlight.

Effective lighting design ensures brightness is limited to the minimum necessary for its purpose. For indoor spaces, task-based lighting focuses illumination precisely where needed, avoiding excessive brightness. Outdoors, unnecessary brightness contributes to skyglow, obscuring the night sky and disrupting ecosystems. In traffic areas like roads and parking lots, lighting should balance visibility and spillover control, while lower brightness levels are typically sufficient for pedestrian pathways to enhance safety and minimize intrusion.

By carefully managing brightness, we can reduce light pollution, conserve energy, and foster a more sustainable and harmonious nighttime environment.

Strategies to Mitigate Light Trespass

Reducing light trespass requires thoughtful planning, responsible lighting design, and effective communication. By taking these steps, you can safeguard the nocturnal environment while addressing both personal needs and broader community impacts.

Examine Your Property

Start by evaluating your own lighting setup. Assess whether fixtures are properly shielded and consider adjustments that can reduce light spill without compromising safety. In some cases, you may find that certain lights are unnecessary and can be removed entirely. Even small changes, such as angling lights downward or reducing their intensity, can make a significant difference.

Engage with Your Neighbour

If light trespass from a neighbour’s property is causing discomfort, it’s essential to approach the situation with understanding and cooperation. Begin by evaluating whether changes on your own property could help resolve the issue. When speaking with your neighbour, adopt a constructive, solution-oriented approach: calmly explain the problem, listen to their perspective, and work together to find a resolution. They may not even be aware that their lighting is causing a disturbance, and concerns about security or other factors might arise. Approach these concerns with empathy, aiming to find common ground. Be ready to propose practical solutions, such as re-aiming lights, adding shields, replacing fixtures, or turning lights off when not in use. Clearly express your needs, but remain open to compromise that benefits both sides. Familiarizing yourself with local outdoor lighting regulations can also provide useful context to guide the conversation.

Adopt Responsible Lighting Practices

Incorporating thoughtful design principles into your lighting setup can help minimize light trespass while maintaining functionality:

• Use fully shielded fixtures to prevent light from spilling above the horizon or into unintended areas.
• Opt for the lowest illumination levels necessary for visibility safety, particularly for pathways and outdoor spaces. Consider alternatives like phosphorescent markers or reflective coatings for subtle, low-impact lighting.
• Natural barriers, such as trees, shrubs, or fences, can help contain light within a specific area and reduce its impact on the environment and neighbouring properties.

Control Lighting Timing and Indoor Spill

Set outdoor lights to turn off automatically within a few hours of sunset using timers or smart lighting solutions. Indoors, reduce light spilling through windows by using curtains or shades, especially during nighttime hours. These simple measures can significantly reduce unnecessary light exposure.

Limit Blue Light Emissions

Remember, when choosing light fixtures, prioritize those with minimal blue light output. Avoid light sources with a colour temperature exceeding 3000K, such as metal halide lamps or cool white LEDs. Instead, select warm or amber-coloured lights in the range of 2200K to 3000K, as these are less disruptive to human health and wildlife. This is an important consideration in addition to minimizing light trespass.

By implementing these strategies, you can address light trespass effectively, foster positive relationships with neighbours, and contribute to the preservation of the natural nightscape.

Conclusion

The Royal Astronomical Society of Canada (RASC) and its Light Pollution Abatement Committee (LPAC) play a pivotal role in guiding communities and individuals toward effective lighting practices. By adopting these strategies, we can create a balance between necessary illumination and the preservation of dark skies. Whether it’s retrofitting outdoor fixtures, advocating for community-wide bylaws, or simply using responsible lighting at home, everyone has a part to play in mitigating light trespass.