What is Light Pollution?

When I first started learning about best practices for installing outdoor lights, I came across some articles that warned about the effects of landscape lighting on the environment. Ever hear of light pollution? If you have and you’re wondering, “what is light pollution?” then this article is for you.

In short, light pollution refers to the negative effects of artificial lighting on the environment and all of its inhabitants. A good way to familiarize ourselves with the subject is by delving into some of its more prominent elements. So, in this article, we’ll look at some important terms that you should know about before you install your landscape lighting system, or if you already have a outdoor lighting.

Sky Glow

Sky glow is a natural occurrence, produced by celestial objects – the sun, moon, stars, nebulae, etc. But, the world’s collective use of electrical lighting can obscure some of these night-time sights and interrupt natural cycles. Human-created sky glow, the illuminating of the sky at night by way of artificial light, is one cause of these environmental alterations and falls under the heading of light pollution.

The phenomenon of sky glow results from light sources that point toward the sky and those that do not have sufficient shielding. It is also a consequence of light reflecting from a surface, or multiple surfaces, toward the ground, which increases the visibility of the resulting glow. Because of the growth of the landscape lighting market, sky glow is often mentioned in relation to residential lights.

Still, other sources of night-time light, such as lighting for commercial structures, urban landscapes, Christmas and events, streets and major roads, tunnels and galleries, campuses and other areas, also contribute to the brightness of the glow. And much of this light reflects off of natural elements, like dust particles, molecules of gas, and water. This reflection creates a mass dispersal of light that contributes to sky glow.

Glare

The term, glare, refers to excessive brightness produced by artificial lighting. It can occur when a light source is exposed, due to partial or no shielding on the fixture, or when a source of light points toward the sky. Spotlights, which enable the installer to aim the light source high or low, and uncovered luminaires, like in-ground well-lights, can work against a smooth, well-blended arrangement of light and darkness. The result is an uncomfortable experience for the eyes. Additionally, bulbs capable of high light output can contribute to glare, causing eye strain, subsequent headaches and other forms of discomfort.

Over-Illumination

Over-illumination can also refer to light that is too bright. But, it differs from glare in that its application is more specific. While glare refers to excessive brightness in general, over-illumination refers to light that is too bright for the particular activity that the light is intended to support. A common example appears in the form of buildings that employ natural light from a skylight in conjunction with artificial lights in the same area. You might find this condition in some museums, office buildings, and the like, where workers perform daily tasks.

Commercial buildings where lights remain on overnight, after most or all employees have gone home, are also examples of over-illumination. And the term is often used in reference to residential areas to describe occasions when a light is left on in an unoccupied room, or when a home’s outdoor fixtures emit light that is unduly bright for the task of providing illumination for a party or accentuating features of the landscape. Whether the site is a grocery store, a warehouse, or an otherwise cozy home, over-illumination can produce significant consequences for those exposed to it.

Prolonged exposure to excessively brilliant light can induce migraine headaches, which could mean a higher chance of brain lesions and disrupted blood flow for the affected persons. It can cause fatigue, impairing employees’ ability to perform at their best in the workplace. It can also lead to hypertension, cardiovascular disease, and other illnesses. In addition, over-illumination disrupts the natural cycles of various kinds of animals, as well as those of human beings.

Light Clutter

Too many artificial light sources arranged together in a particular space produces a phenomenon known as light clutter. Often a consequence of such night-time luminaries as business lights and inappropriately organized streetlights, light clutter is sometimes the unintended result of an attempt to provide visible working environments, security for pedestrians, and a means of safe automotive travel at night. Other times, it is the result of an intention to create eye-catching street-level fare.

Particularly in the case of illuminated advertisements, some light sources are designed with the hope of drawing the attention of travelers as they commute to various destinations. Traditional brightly-lit billboards, orbital billboards, and storefront lighting, are all examples of advertisements that are used to grab attention. Accordingly, where these sources are crowded together, they can create a quality of light that obscures the presence of various objects, whether these objects are mobile or stationary.

Of course, light clutter can also occur in our own yards. A landscape lighting design that works against providing a fair amount of distance between light sources produces effects in residential areas that are similar to those that we find in more industrial areas. And, because it is closer to home, it also increases the chances that light clutter will directly affect homeowners and their families while they are in the house.

Light Trespass

Light trespass describes those instances when light shines in undesired areas. More specifically, the term applies to light shining onto another person’s property, or into their home. This can occur as a result of a contractor’s neighborhood design, where lighting is incorporated into the design, or as a consequence of a neighbor’s landscape lighting. In both cases, the person whose property becomes the recipient of the trespass, could find themselves exposed to the whole range of photo-pollutants – from sky glow to light clutter.

Dark Sky Lighting

Dark sky lighting is not a form of light pollution. On the contrary, it is a set of guidelines that can help minimize the incidence of light pollution in areas where light sources are likely to be used with great frequency. The primary aim of dark sky lighting is to use only the kind and number of light sources necessary in a responsible fashion.

According to the International Dark Sky Association, there are five principles that we can use to decrease light pollution. We can begin by determining whether a particular light, or set of lights, serves a specific purpose beyond the singular aim of enhancing aesthetic appeal. If the light is not required for a certain function, like security or safety when walking the landscape at night, then the light is not essential.

We should also be careful to direct the light of a luminaire only to the area where it is needed. Here, using a light that is appropriately shielded, so that little or no luminescence crosses into unintended areas, is important. If any of our lights do reach into unintended areas, then it’s a good idea to check whether we can change the placement of the fixture (likely with respect to its height, as a higher positioned light increases the potential for light trespass) and the direction in which the fixture aims its light. If neither of these measures are possible, then it is probably best to replace the light fixture (or to have it replaced).

Limiting the degree of brilliance that a fixture emits is also a key principle of dark sky lighting. This is particularly important, given the fact that surfaces can reflect light and, ultimately, contribute to sky glow. We can allow for environment-friendly lighting by using bulbs that emit only the least amount of light required to serve the specific function of a given light fixture. For this, we will want to know the degree of brightness that a given bulb produces.

(A bulb’s brightness is measured in lumens. The latest bulbs often come with a Lighting Facts Label that tells you about a bulb’s level of brightness, the estimated yearly energy cost, the life of the bulb, its light appearance with respect to warmth and coolness, and the energy used in watts.)

A fourth principle of dark sky lighting entails controlling the duration of time for which our lights would be used. Much of this control can be accomplished through automated means. Motion sensors and timers can help ensure that the lights only come on when someone comes within a certain distance of the sensor, or at a time of our choosing, rather than running for an indefinite period of time. Of course, these lights would turn off as soon as the person has moved out of range of the motion detector, or when the light’s preset time-limit expires.

Finally, we can help produce darker skies by taking care to select warm outdoor light sources for our homes. Bulbs that operate at Kelvin ratings higher than 3000 generally emit blue or cool white light. These colors of light are known contributors to light pollution and have a greater chance of disrupting the natural cycles of people, plants and animals, than warmer light. A bulb with a Kelvin rating of 2700 (or less) is usually a better choice for residential landscapes and, consequently, a better choice for our environment.

According to ScienceMag.org, roughly 83% of all of the people in the world live in areas affected by light pollution. And, approximately 80% of people living in Canada and the U.S. alone can no longer see the Milky Way, because of atmospheric brightening by artificial light. But, by applying dark sky lighting principles, we can reverse these conditions and their effects. For a comprehensive look at the ways in which you can alter your landscape lighting to protect the environment, visit Darksky.org.

I hope you’ve found this article informative. Please feel free to peruse the rest of the website for more information on landscape lighting.