Lighting Design: Considering the Impacts of Light Pollution (Dark Sky)

by Yvonne English, RLA, LEED AP, ASLA, IDA, IES

The International Dark-Sky Association (IDA) has a "Glare Metrics" program , a joint effort between IDA and Ian Lewin, of Lighting Sciences, Inc. This program is designed to create a standard of accurately and uniformly measuring glare, primarily by looking at intensity, luminance, and luminance contrast.

"The problems of light pollution first became an issue in the 1970s when astronomers identified the degradation of the night sky due to the increase in lighting associated with development and growth. As more impacts to the environment by lighting have been identified, an international "dark sky" movement is advocating for the precautionary approach to outdoor lighting design."
"?u Model Lighting Ordinance

What is light pollution? It's any adverse effects resulting from not properly shielded outdoor lighting. An unshielded light source allows light directed where it is not wanted"?uinto people's eyes and the night sky.

There are four forms of light pollution:

Sky glow: light shining into the night sky above the horizon. This is the brightening of the night sky by artificial light. Contributors are uplighting and reflected light.


Light trespass: light directed into areas where it is not intended, wanted, or needed, such as poorly shielded or poorly aimed fixtures.

Glare: light that shines into our eyes, causing visual discomfort and decreased visibility.

Clutter: a combination of all three, bright, confusing, and excessive groupings of light sources, commonly found in over-lit urban areas

Why Is Light Pollution a Threat?
Light pollution causes multiple issues. Some are obvious, but many are not, and not easily related to light pollution. The obvious threats:

1. Our views of the skies have drastically changed over the past 60 years. The view from a 
mountain top may be similar to night sky views from the 1950s, but the views of the urban skies are much different. The children's song "Twinkle, Twinkle, Little Star" has little meaning during the night in urban cities. Views are impacted primarily by the sky glow and clutter of artificial light.

2. Light trespass is a violation of property rights. An example is the typical spot light on the side of a home, which usually produces light that crosses into the neighbor's property. Such lighting can penetrate bedroom windows and disrupt sleep.

3. Our safety is greatly impacted by glare, which can temporarily blind people, particularly youngsters and the elderly. Glare is harmful, not protecting.

Our health, the health of wildlife (which impacts the health of our planet) and wasted energy are the less understood threats of light pollution. How does light pollution impact our health? Light affects our natural circadian biological rhythms, which in turn impacts our health. In 2012, the American Medical Association issued a report on the health effects of light pollution, which in part stated: "The natural 24-hour cycle of light and dark helps maintain precise alignment of circadian biological rhythms, the general activation of the central nervous system and various biological and cellular processes, and entrainment of melatonin release from the pineal gland. Pervasive use of nighttime lighting disrupts these ... processes and creates potentially harmful health effects ..."

The report further states: "More direct health effects of nighttime lighting may be attributable to disruption of the sleep-wake cycle and suppression of melatonin release. Even low intensity nighttime light has the capability of suppressing melatonin release. In various laboratory models of cancer, melatonin serves as a circulating anticancer signal and suppresses tumor growth. Limited epidemiological studies support the hypothesis that nighttime lighting and/or repetitive disruption of circadian rhythms increases cancer risk."

Nocturnal mammals, birds, amphibians, reptiles, insects, and fish experience similar disorientation as humans when there is too much artificial nighttime light. Behavior governing mating, migration, sleep and finding food are determined by the length of nighttime. Light pollution negatively disrupts these age-old patterns, which in turn causes habitat disturbance, changes in behavior and impacts survival.

International Dark-Sky Association (IDA) and the Illuminating Engineering Society (IES) co-wrote the Model Lighting Ordinance (MLO). It includes the use of lighting zones and luminaire ratings. The MLO will allow communities to drastically reduce light pollution and glare and lower excessive light levels. The recommended practices of the IES can be met using readily available, reasonably priced lighting equipment.

Energy
Energy, of course, is a big environmental concern, as is the pollution associated with fossil fuels and generating electricity.

Editor's note: The IDA information sheet "Economic Issues in Wasted and Inefficient Outdoor Lighting" notes the 175 watt dusk-to-dawn mercury vapor light is a common outdoor fixture used throughout the U.S. Such a system actually uses about 210 watts of overall energy (when considering the ballast and other factors). This paper contends that at least 30 percent of such lighting is totally wasted. Tucson, Ariz. had over 20,000 such lights until a mass change out to better lighting was made. The annual operating cost of those mercury fixtures in Tucson was nearly $1.4 million. The projected extrapolation for that kind of lighting across the U.S. is $700 million!

What Can We Do?
Some simple steps during designing the outdoor lighting can make a big difference. Establish careful lighting goals; use less light; and direct light carefully.


With careful planning, we can mitigate light pollution risks in several ways:

Establish Your Lighting Goals: Lighting for safety means illuminating pathways, stairways or changes in elevation.
Security lighting means providing a soft light along the borders of a property. Remember to carefully place spot lights, which can add glare and actually attract intruders. Provide task lighting where needed, such as cooking, dining, entertaining spaces. And of course, provide beauty and interest at night.

Less light is more effective: Light only the goals. Use lower wattage lamps and beam spreads. Direct light only where it is needed, which minimizes "spill"and increases safety from glare. Down lighting should be almost straight down to reduce clutter, and uplighting straight up to reduce scatter. Hide the light bulb source to reduce glare. Incorporate zone controls to turn off unnecessary light and energy.

About the author: Yvonne English has been adding nighttime dimension to her landscape designs since 1995. She is a member of International Dark-Sky Association (IDA), the first organization in the dark-sky movement, and the Illuminating Engineering Society (IES). IDA and IES worked together to write the Model Lighting Ordinance (MLO) www.darksky.org/assets/documents/MLO/MLO_FINAL_June2011.pdf, which could affect future lighting design. It defines lighting zones and a luminaire rating system.