Light Pollution v. Trespass

By Randal Smith

www.lightingdesignlab.com

An awareness of the consequences of night lighting is growing among lighting specifiers. Communities are drafting ordinances designed to control skyglow and unwanted light across property lines. The issues are called light pollution and light trespass, and they can be easily confused.

Light pollution is when the illumination from a property, or a community is directed upward into the sky. This has the effect of causing the night sky to literally glow over that area. The sky glow blocks out the view of the night sky for all of us. It makes the work of astronomers nearly impossible. It ruins the atmosphere of small towns and rural areas at night. Many communities feel that the darkness is an important reason why they moved to the small towns in the first place.

Light trespass is when a luminaire of the wrong distribution is used on a property, and the light is being distributed in improper directions causing other property owners to experience glare on their property.

Dealing with these problems is gaining in importance partially due to several issues. The Leadership in Energy and Environmental Design (LEED) program offers a credit for controlling stray light on a project. Some communities are adopting the Model Lighting Ordinance. A greater environmental awareness is growing in the lighting community, prompted by the International Dark Sky Association and the Illuminating Engineering Society of North America.

The causes of light pollution and light trespass are not always the same things, and neither are the solutions. But using luminaires with optics designed for better cutoff of light distribution can be a good start toward helping solve both problems. A free publication is available from the Lighting Research Center.

A terrific guide to light pollution and trespass is available at no cost from the Lighting Research Center's National Lighting Product Information Program's Lighting Answers website at http://www.lrc.rpi.edu/