Over the last half a century, we have become more and more aware of our environmental impact. Modern efforts abound to reduce pollution. Whether it is reducing plastic in our oceans, smog in our air, or chemical runoff in our streams, both individuals and government agencies have fought to preserve our planet. However, one type of pollution has gone mostly unnoticed, even as it grows worse and worse and has some obvious effects. Light pollution is robbing billions of people across the globe of the chance to see the night sky. But the damage is not just cosmetic. Light pollution can be harmful to wildlife, make scientific study more difficult, and cause harmful disruptions to human biological cycles. So before you install your own outdoor lighting, it is essential that you familiarize yourself with the best practices to avoid spreading light pollution.
What is the Big Deal with Light Pollution?
The International Dark-Sky Association (IDA) is the leading organization in the fight against light pollution worldwide. They define light pollution as “the inappropriate or excessive use of artificial light”1 that results in a number of undesirable outcomes. One of the primary concerns with the spread of light pollution is the creation of sky glow. Sky glow is the ambient reflected light from a human settlement (usually a town or city) that lights up the night and obscures the night sky.
The problem with skyglow is that it diminishes the effects and benefits of nighttime darkness. For wildlife, nighttime darkness can be vital to their very survival. Many animals hunt at night. But when the night never becomes fully dark, hunters aren’t able to hide as well, and their primary food source can be threatened. In addition, some animals only awake in full darkness. When the night never becomes completely dark, the activity cycle of some animals can suffer.
In addition to the effect on wildlife, sky glow can make it harder for scientists to study the night sky. One hundred years ago, you could find a brilliant night sky almost anywhere on earth. The Milky Way shone bright overhead no matter where you were. Today, scientists studying the stars have had to move their telescopes father and farther into the wilderness, away from the bright lights of human habitats. As the number of dark sky locations shrinks and the sites become more remote, opportunities for clear observation have become scarce. Scientists have to book time on large telescopes that are shared among thousands of researchers. Even once the time is reserved, conditions can be harsh and the telescopes hard to access. Often, weather and other factors completely ruin the precious bit of time a researcher has with the telescope.
Reducing Light Pollution from Outdoor Lighting
In an efforts to protect the night sky, some cities and towns have begun to pass ordinances limiting artificial light at night. Some towns in rural areas actually market themselves as dark sky locations, far from the bright lights of the city. To protect their reputation and the astro-tourism that comes with it, these cities have placed strict limits on the use of artificial lights after dark.
Even in areas where nighttime light is not regulated, individual homeowners can and should take steps to reduce their contribution to light pollution. There are three main factors that both contribute to light pollution and are the keys to reducing it:
- Light Fixtures
- The Type of Light
- When the Lights Are Used
By controlling these three factors, individual homeowners can reduce light pollution while still enjoying beautiful outdoor lighting that fulfills all of their needs.
Light Fixtures that Reduce Light Pollution
One of the most effective ways to reduce light pollution is to use the right kind of light fixture. When you install outdoor lighting around your home and your landscape, you want it to shine in a particular area for a specific purpose. The light that escapes in directions other than where you need and want it is called light trespass. Light trespass can result in unwanted glare that shines into a bedroom window, your neighbor’s yard, or up into the sky where it contributes to sky glow. Reducing or eliminating light trespass is the best way to reduce light pollution.
When avoiding light trespass, the key is to use light fixtures with shields that keep the light from exiting the fixture in any direction other than where you need and want it. The extent to which a fixture prevents light trespass is called its cutoff.
According to standards published by the Illuminating Engineering Society of North America (IESNA),2 a full cutoff fixture allows no more than 2.5% of the fixture’s brightness to shine above a 90-degree angle from the fixture and no more than 10% above an 80-degree angle. A partial cutoff fixture allows slightly more glare, with no more than 5% of the fixture’s brightness shining above a 90-degree angle and no more than 20% above an 80-degree angle. A non-cutoff light fixture has no limit on the amount of light that shines upward from the fixture and is not recommended.
The Type of Light
One of the most significant factors in light pollution, besides the actual amount of light that escapes upward from a light fixture, is the type of light. The warmth or coolness of light is measured in degrees Kelvin (K). A warmer, yellower light has a low light temperature, around 3,000K. Cooler blue or white light is usually 4,000K or more. In general, warmer light is less harmful to the environment. The human eye, along with many other creatures, is especially sensitive to blue light. On the opposite end of the spectrum (literally), red light does not disturb most nocturnal animals and has little effect on human vision. That’s why astronomers use red light to see their equipment since it does not cause the pupils to constrict, which would make it harder to see dim stars.
The IDA recommends light at 3,000K or less, in other words, warm light. The low-pressure sodium lamps used in many older commercial lighting systems are ideal since they emit a warm orangey light. However, many newer commercial systems and most residential systems do not use low-pressure sodium lamps, because their orangey light has poor color rendering and can look unpleasant. Instead, many commercial lighting systems and almost all residential systems are switching to more efficient LED lamps.
LED lamps have many benefits, including their efficiency and long lifespan, but they also pose risks. Many LEDs give off white light, which is excellent for color rendering but too high on the color temperature scale, at 4,000K or above. That cool light is most damaging to the environment. Instead, using 3,000K lights is an excellent compromise between color rendering and light pollution prevention. Also, many lighting designers actually prefer 3,000K LEDs for their softer, calmer appearance.
When Lights Are Used
The best way to avoid light pollution is to turn off the lights. Of course, just turning off all the lights would defeat the purpose of outdoor lighting. But light can be limited.
Decorative lights should be kept on timers that turn them off by 11:00 p.m. when most people have gone to bed and the lights are no longer necessary.
Functional lights that are used to see in a particular area should be turned off when not in use. Installing these lights on their own circuit makes it possible to turn them off without affecting decorative lights. Even better would be to use motion sensors that automatically turn off the lights when no one is around.
Finally, security lights should be off most of the time and should only turn on when triggered by motion sensors. Security lights that suddenly turn on when someone approaches are just as effective as lights that are on all the time but create much less light pollution.
High-Quality Outdoor Lighting Installation
If you are looking for a trustworthy company to install your outdoor lights, you are in luck. TrustDALE has done the research and can recommend Night Vision Outdoor Lighting as your residential landscape lighting specialists in the Southeast. Their experts can help design a system with minimal light pollution and maximum usefulness. They are also backed by Dale’s trademark $10,000 Make-it-Right Guarantee™.
1. “Light Pollution.” International Dark-Sky Association, The International Dark-Sky Association (IDA), 13 Feb. 2017, www.darksky.org/light-pollution/.
2. “What Are the IESNA Cutoff Classifications?” Lighting Research Center | Education | Learning | Terminology | Spectral Power Distribution, Rensselaer Polytechnic Institute, www.lrc.rpi.edu/programs/nlpip/lightinganswers/lightpollution/cutoffClassifications.asp.