Landlords’ Guide to Light Trespass and Light Pollution in Rental Properties – And What to Do About it

By Eric Weld, MassLandlords, Inc.

If you or your tenants are experiencing insomnia, headaches, depression, increased anxiety, unexplainable weight gain, tired eyes, frequent sickness or other health problems, you should check the nighttime lighting around your home and rentals.

Unshielded bright nighttime light like this one wastefully projects a third of its beam into the sky while casting an obtrusive and harmful glow on nearby residents. A simple light shield affixed to the bulb could direct light downward and protect neighbors from light trespass and its negative health effects. Cc by-sa Wikimedia commons soccordudeTY22

Are you or your rental units victims (or perpetrators) of light trespass and light pollution? Maybe you live or own units on a corner or part of the street with a streetlight shining through the night. Or your rentals are located across the street from a busy convenience store/gas station or car dealership with blinding light saturating the entire neighborhood into the wee hours.

With a lot of light pollution research in recent years, we know that excessive nighttime light is more dangerous than previously realized. If left unattended, obtrusive nighttime light can result in a range of adverse health effects, from mild to fatal. You read that right. Light pollution that prevents adequate sleep has been linked to a malignant list of maladies: cardiovascular disease, Alzheimer’s, prostate and breast cancer, type 2 diabetes, hypertension and other metabolic-related illnesses that can lead to death.

Beyond direct health concerns, light pollution also harms our environment and wildlife habitats, greatly impacts our quality of life, obscures views of the night sky, stars and constellations, and reduces safety by creating blinding glare and shadows where, perversely, attackers can hide. The scientific evidence on the efficacy of light in reducing crime is very mixed.

This map illustration captures nighttime views of humans’ light projections around the world. Not surprisingly, the United States and Europe represent the most-lit areas of the world. In the U.S., 99% of the population experiences some kind of light pollution. Cc by-sa Wikimedia commons Dominic Alves

What Can Landlords Do About Light Pollution?

Light Shields

Fortunately, light pollution and trespass, unlike air and water pollution, are easily and cheaply controlled. And unlike noise pollution, it doesn’t even require difficult-to-enforce changes in behavior or schedules.

If you have floodlights or other nighttime lights installed on the exterior of a dwelling and lighting up more than the intended area, you should consider affixing light shields. Because light is blockable and directable, light shields can sheathe unwanted light streams and allow more nighttime darkness for those accosted by unwanted light.

These simple, inexpensive products simply clip on to a light fixture or bulb and direct the light downward, limiting lateral light from trespassing on neighbors’ property and into their homes. For your tenants complaining of exterior porch or garage lights left on all night, light shields, often priced around $50 or less, can provide a quick, inexpensive solution.

Light shields and light hoods come in a variety of shapes and sizes. Some light shields are partial corner hoods that prevent light from leaking in a certain direction. Others are fully round shields that can attach to the bulb of a floodlight and concentrate the light beam downward instead of all around, such as onto neighbors’ homes.

Gary Citro, a sales representative with Parshield, a light shield company based in Pennsylvania, says he receives many requests from landscape architects and residents responding to light trespass complaints. Parshield exclusively sells PAR-38 light shields. These fully round shields attach to PAR-38 bulbs, a commonly used bulb for outdoor floodlights.

“The light trespass problem is brutal,” notes Citro, who, as an amateur astronomer, has inherent interest in mitigating light pollution. “Our light shields are an easy way to control light trespass.” Citro is quick to emphasize his company is not invested in dowsing all light. “We’re not against lighting,” he explains, “just against light that shines up into the sky and erases constellations and presents danger. We want the light to shine down on the ground where it’s intended.”

DarkSky International is a community of volunteers committed to limiting light proliferation and pollution and retaining darkness at night. The organization suggests, if your neighbors or other tenants are shining obtrusive light onto neighbors’ space, to first talk to them, informing them of the light trespass and suggesting solutions like light shields. Depending on where you live, your city or town might have a light ordinance to point to. If your town does not have a light trespass law, DarkSky encourages you to consider suggesting one.

More Light Pollution Solutions

Light shields may be the simplest solution to light trespass, but not the only one. Automatic light dimmers, motion sensors and timers can also be installed to manage light pollution and lower average exposure to light. Anyone shining light through the night needs to ask if constant light is really necessary. Can your security lights be set to turn on with motion detected in the area? Motion sensors can be set to highly sensitive detection levels, even to the point of flipping on a bright wash of light when a rodent passes by, and are plenty sufficient to deter an unwanted intruder or criminal.

Sources of light also play a big role in pollution. Some light fixtures are preferable to others. Unhooded fixtures that produce glare and spew light laterally and into the sky should be avoided. There are very rarely any reasons for residents and businesses, other than airports, to light up the night sky. There are numerous light fixtures available, for small and larger areas, that aim light downward and shield it from trespassing on neighbors.

Interior lights in offices not used at night should be turned off. Light from office buildings bleeds out through the windows and lights up the night sky.

Bulbs, too, make a difference. Both LED and incandescent lightbulbs come in a variety of brightness levels, measured in lumens. LED bulbs can project the same level of lumens (projected light visible to the eye) as incandescent bulbs, but use much less wattage, or energy. When switching from incandescent to LED bulbs, be careful not to match the wattage, because an LED bulb using similar wattage will project much brighter light than the incandescent bulb it replaced. Instead, replace lights based on equivalent (or lower) lumens.

Both types of bulbs also come in a range of light colors or light temperatures (more on this in a minute). When purchasing LEDs for nighttime lighting, be sure to choose “warm-colored” bulbs – that is, those comprising red and yellow hues as opposed to blue and green hues.

Blue Light vs. Red Light

To explain: All light is a spectrum of colors ranging in hue across a prismatic rainbow with various shades of blue, red and green. As the colors combine, they are usually perceived in our retinas as a white or bright yellowish glow. Light-emitting devices – lightbulbs and electronic screens – utilize a range of color spectra, some emphasizing “cooler” colors like blue and green, others favoring “warmer” reds and yellows.

Light color, or light temperature, is rated in Kelvin (K), from 1,000K to 10,000K. (Named after 19th-century British physicist Lord (William Thomson) Kelvin, who proposed the rating system in his publication On an Absolute Thermometric Scale, 1848.) Lower K values indicate light that contains warmer colors and less blue hue. Different colored tones of light have different effects on our eyes, brains, circadian rhythms and health. Optimal light for the human eye is in the range of 2,000-3,000K.

Light from our sun is a higher K value, nearly 6,000K, than we would want shining into our homes (though our sun is very low in blue light compared to the average star). Blue light triggers our bodies’ natural response to be awake and alert. Hotter light tones, favoring reds and yellows, are rated lower K, and generally signal our brains to mellow and prepare for rest. These are ancient impulses programmed in our brains, adapted from millennia of cycles living according to the sun’s daily rhythms. Thomas Edison invented the incandescent lightbulb in 1879 and ushered a new era of nighttime lighting, now on steroids. Our relatively short period of electric light at night has not altered our natural circadian rhythms – dictated by the sun and evolved over millions of years – and need for nighttime rest.

Unfortunately, we live in an age in which electronic devices proliferate. Televisions, computers, tablets and smart phones all emit blue-favored (higher Kelvin) light. These light emissions stimulate our brains and signal our alert responses. For that reason, blue-light filters – attached as screen protectors to computers and phones or coated onto lenses of reading glasses – will assist users in better rest and sleep after engaging with screens at night. Ideally, you should power down electronic screens a couple hours before sleep time.

Use of LEDs has also increased for exterior nighttime lighting, such as floodlights. This is a good development for energy reduction. But LEDs – such as those used in tablet and telephone screens – naturally emit more blue light unless altered or chosen specifically for softer light. So not only is your LED floodlight trespassing on your neighbors’ darkness, its typically blue-tinted light is also triggering their natural response to wake up.

When purchasing LED bulbs for your exterior floodlight, be sure to choose lower K bulbs, favoring red hues. These are available for floodlight and exterior use. And be sure to attach a lightbulb shield.

This streetlight is half shielded, fitted with a fully round shield painted black on one side, presumably blocking light trespass toward residents on that side, while scattering light through the glass hood on the other side. Cc by-sa flickr flipflopflorida

Why is Light Trespass Bad for Us?

The main reason excessive light at night is so detrimental is that it hinders or disrupts our bodies’ rest cycle. Without proper rest, including between seven and nine hours of sleep within every 24 hours, the human body loses ground on several fronts in the quest to remain healthy. Most bad health outcomes from too much light exposure are a result of no or poor sleep.

For ideal sleep, the body needs melatonin, a hormone produced and released by the pineal gland. Located in the center of our brains, the pineal gland helps regulate our sleep-wake cycles, called our circadian rhythm, and influences cardiovascular and reproductive systems.

Melatonin helps prepare our brains and bodies for deep sleep. Our natural production of melatonin is triggered by darkness and suppressed by light, especially blue-tinted light. Melatonin assists quality rest and sleep, an absolute necessity for optimal health. In general, a lack of melatonin when it’s time to close your eyes results in a less restful and rejuvenating sleep.

When we sleep, our bodies: release human growth hormone that helps repair muscles and bones; restore and refresh mental and physical energy; and rev up our innate and adaptive immune responses, which help ward off an onslaught of disease and viruses in our daily environments. Without adequate sleep, all of these functions can falter, opening the door to threatening pathogens and destructive cells that can shorten lives and severely curtail life quality.

Lack of adequate sleep can lead to a list of bad health outcomes, but it’s usually a cumulative effect, a subtle problem that compiles over time. The body and mind are bafflingly complex. Small problems over a long period add up in surprising ways. Why do food dyes and additives make some of us sick? Why can some of us eat gluten or shellfish while others might be severely threatened by such foods? Light at night that interrupts our natural ability to sleep and heal will have different effects on different people.

But light pollution and trespass are easily fixable. It’s ironic that millions of Americans are harmed and sickened by disrupted sleep due to invasive indoor or outdoor lighting while a few simple remedies are readily available to address this vital but underemphasized problem. There is no reason anyone should suffer from health-harming sickness due to obtrusive light preventing good sleep, despite our culture’s increasing nighttime light encroachment.

The smaller, unshielded bulb at left produces more light trespass than the larger, brighter shielded PAR-38 at right.

How Does Light Pollution Hurt Animals, Plants and Biodiversity?

Edison’s invention of the incandescent lightbulb expanded our days and productivity endlessly into the dark night (and ended our unsustainable practice of killing every whale in the sea for their oil). An increase in nighttime lighting has not abated since. Our nighttime sky brightness has increased 10% every year from 2011 to 2022. In the United States, 99% of people experience some form of light pollution or exposure to unnaturally high levels of light in the evening, from both indoors and outdoors.

Much of the increase of nighttime lighting is based on the mistaken belief that more light equals more security. There is no evidence to support that premise. In fact, it’s been shown that bright light can decrease safety from attackers because it creates hard shadows where a person can hide, shielded from view by the light’s glare. Bright nighttime lighting, such as that at gas stations and car dealers, can create massive glare spilling onto the street where it can partially blind passing drivers and decrease visibility.

Beyond acute harms to human health, artificial nighttime lighting threatens plants and animals. Animals, of course, need their sleep, too, to remain healthy. But nighttime light also affects predation by making pollinators easier to see and be eaten; by damaging birds’ visual pigments and deterring their migration; by disrupting essential breeding patterns, growth and activity.

Plants and trees have natural circadian rhythms, too, just like humans. When they are disrupted by artificial nighttime light, plants’ growth cycles are altered. A tree standing in a bright nighttime light may delay its leaf senescence, flowering and important winter dormancy that protects it from cold weather and enables it to survive winter.

Like warming trends, excessive nighttime lighting’s harms to animals and plants could eventually impact humans’ food, medicine supplies and general biodiversity.

What Can Towns and Cities Do About Light Pollution?

It may be late in the game, but many towns and cities have begun taking action against light pollution and light trespass.

Depending on where you live, some forms of light trespass might be in violation of municipal ordinances. In Massachusetts, 57 cities and towns – out of 351 – have bylaws defining and regulating outdoor lighting.

Not surprisingly, the state’s large urban centers – Boston, Worcester, Springfield, etc. – have not yet regulated light pollution. Communities with light pollution ordinances tend to be small to mid-sized.

Amherst, for example, is inclusive of lighting situations and solutions in its exterior lighting regulation, part of its zoning bylaws. Section 11.2417 specifies: “Protection of adjacent properties by minimizing the intrusion of lighting, including parking lot and building exterior lighting, through the use of cut-off luminaries, light shields, lowered height of light poles, screening or similar solutions.”

Closer to Boston, Cambridge limits lighting in parking facilities “so as not to reflect or cause glare on abutting or facing residential premises nor to cause reflection nor glare which adversely affects safe vision of operators of vehicles moving on nearby streets” (section 6.46). The city also defines usage of outdoor floodlighting and decorative (holiday) lighting to be “installed in a manner that will prevent direct light from shining onto any street or adjacent property” (section 7.20). The ordinances were an outcome of an Outdoor Lighting Ordinance Task Force appointed in 2013 to study the issue of light trespass and light pollution citywide.

These local bylaws can assist and help resolve light trespass disputes. But as DarkSky International points out, a lighting ordinance on the town books doesn’t do the job of regulation by itself. And even for towns with light trespass bylaws, enforcement is often unclear.

Most likely, light trespass disputes will be resolved through in-person interaction and negotiation between neighbors, tenants and landlords and tenants. In some cases, landlords might consider paying for light shields.

If your sleep is being disrupted by light trespass, and you’ve tried unsuccessfully to get lights turned off or shielded, you might have to resort to defensive measures. Blackout curtains, which come in a range of sizes, colors and styles, are an effective and inexpensive way of closing off exterior light at night. If that’s not feasible, a wide variety of sleep masks are available, starting at only a few dollars.

Too Much Nighttime Light

In general, our high level of nighttime lighting is unnecessary, wasteful and harmful. Some 35% of artificial light is lost to the night sky due to improper shielding and aiming light beams. We would all benefit in countless ways from a nationwide off switch of unneeded nighttime lights.

More awareness is still needed. And more communities adopting light trespass ordinances might help. Only 16% of Massachusetts communities have a light ordinance.

To be sure, property owners have a right to operate lights at night on their property. But light trespass is similar to intrusive noise: Everyone has a right to a living space free from both.

For those who do need and use lights at night, a simple light shield will at least keep it from infringing on neighbors’ rights to nighttime darkness.

Shielding and turning off lights at night is essential for their and all of our health.