“Something that annoys your neighbor” is how lighting designer Nancy Clanton, CEO of Clanton & Associates, defines light trespass. Neighbor disputes won’t be solved here, but learning how to avoid light trespass is a relatively simple thing to achieve, explains Clanton.

The easiest way for landscape architects and lighting designers to avoid light trespass is to select lights that have very little backlight and glare. Backlight, Uplight, and Glare (BUG) ratings (per IES TM-15-11) are readily available from lighting manufacturers and provide specifiers with the information they need to minimize trespass in fixture selection and lighting application. Clanton recommends fixtures with B0 and G0, the lowest backlight and glare ratings. “Don’t go above a B1 or G1,” she says.

“Uplight is completely wasted light,” Clanton continues. “There is no reason for it at all. Many cities have lighting codes that state all uplighting has to be U0.” While neighbors mainly notice backlight and glare, people living in multistory buildings can be affected by uplight.

Reducing backlight, uplight, and glare is important for nonhumans as well. A Virginia Tech study of seven soybean fields in seven locations throughout Illinois found that the impact of roadway lighting trespass on plants closest to the road was significant and measurable. Compared to soybean fields with no light trespass, plants affected by light trespass had developmental delays and yield reductions.

Florida has published lighting ordinances for areas where sea turtles are nesting that call for reduced trespass and skyglow along the beachfront. More cities are applying similar regulations for birds during migration. Birds depend on moonlight to guide them, and light trespass impedes navigation.

Clanton & Associates will not light waterways because of the negative effects light has on fish. “We will light a bridge,” she explains, “but all of the light has to be contained on the bridge surface.” She notes that the Colorado cities of Boulder and Denver prohibit lighting waterways.

Light trespass into bedrooms affects sleep, which is not only aggravating but also harmful to our health and wellbeing. It alters a person’s circadian rhythm, which depends on serotonin to be produced during the day from blue light and melatonin to be produced at night from the absence of blue light. While there is some debate among medical and lighting communities on whether it is the color, not the quantity, of light that affects sleep, Clanton believes it is both spectrum and quantity, which is another reason, she says, “to avoid high color temperature lighting.”

To lessen the effects of light trespass on the environment and all species, Clanton shares a method for determining site-specific light trespass levels. First, find out what land use zone the site is in. “Not many municipalities have lighting ordinances, but they do have land use zones,” she says. Lighting Zones are rated from LZ0 to LZ3, depending on residential and commercial density or the Land Use Zone. Once you know the site’s land use zone, assign the lighting zone at the same level as land use. For example, an LZ0 lighting zone might be a nature preserve; a lighting zone of LZ0 would put very little light over its property lines. A lighting zone of LZ1 for a rural residential land use puts a little more trespass across properties. Finally, says Clanton, think back to the BUG ratings of 0, 1, 2, and 3. “An LZ0 lighting zone should be assigned fixtures with BUG ratings of B0, G0, and U0; an LZ1 lighting zone would have maximum BUG ratings to match. The two align, and it really works quite well in determining maximum trespass levels.”

Another Clanton rule is to keep color temperatures (CCT) low in cities; she prefers nothing over 3,000K and preferably 2,700K in residential areas, the places where people sleep. “With LED technology,” she says, “we now have the ability to dim lighting during evening hours and even change color through spectral tuning. It would be ideal to be able to control both dimming and color at different times of day and during migration seasons,” Clanton adds.

Clanton sees an opportunity for landscape architects and lighting designers to help educate land use planners who aren’t always knowledgeable about lighting zones. “I think there is a real opportunity for landscape architects and lighting professionals to help communities understand the relationship between land use and lighting zones and how to address environmental issues with light at night.”

In 2020, the IES and IDA announced a collaboration to address issues of light pollution. Here are their five principles for responsibly lighting the environment.

The Illuminating Engineering Society (IES) and International Dark-Sky Association (IDA) are both resources for landscape architects on the topics of light trespass and skyglow. The IES committee for Lighting for Outdoor Pedestrian Spaces is going through final approval on how to limit light trespass for pedestrian spaces, and the IES and IDA have established a joint committee, chaired by Clanton, that will update the IES/IDA Model Lighting Ordinance. The committee’s charge is to integrate regulations for communities on how to write their outdoor lighting ordinances. LEED site credits for reducing light pollution refer to the Model Lighting Ordinance, and both LEED and WELL Building reference IES and Dark Sky in their certification guidelines.

Nancy Clanton, PE, FIES, FIALD, LC, LEED Fellow

Nancy Clanton is the CEO of Clanton & Associates, a lighting design firm specializing in sustainable and regenerative design. She is a registered Professional Engineer, a member of the National Academy of Science committee on the assessment of solid-state lighting, a member of the WellBuilding “Light” advisory group, a member of the National Academy of Science committee on the assessment of solid state lighting, and an International Standards Organization (ISO) 205 WG 7, USA delegate. Nancy's long list of awards include the 2018 Edison Report Lifetime Achievement Award, the 2014 ACEC Colorado Outstanding Woman Engineer Award, the International CleanDesign Award, and the 2019 IES Louis B. Marks Award. Nancy is also a two-time IES Presidential Awardee. Her past work includes membership on the USGBC LEED Environmental Quality Technical Advisory Group and service as lighting group leader for Greening of the White House. She has led the lighting workshops for the C40 conference in Seoul and participated in more than 3,000 lighting projects with Clanton & Associates.

Learn more about the BUG rating system.