Outdoor Lighting

What Makes a Light Harmful?

This 175 watt Mercury Vapor light produces too much glare, is inefficient, and lights up the sky unnecessarily.

Bad lights do more than just spoil the view of the stars, they can confuse and harm wildlife, create light trespass, waste energy, create glare, and actually reduce nighttime visibility. Bad lights often cost less to purchase and install, but end up costing much more in the lifetime of the fixture.

What Makes a Light Beneficial?

Many good light fixtures are available for homes, businesses, and municipalities that protect the night sky. Shielded or "Full Cut-off" fixtures, such as this, direct all light downward.

Good lighting allows us to meet all the basic needs of lighting (safety, security, visibility, comfort) while having very little negative impact. Good fixtures direct all the light where it is needed, and do not scatter it wastefully into the night or through the neighbor's window. Good lighting incorporates modern, high performance optics that aim light in a defined pattern to reduce glare and light pollution.

Principles of Night Sky Friendly Lighting

• Use outdoor lights only where they are needed
• Direct all light downward by using shielded lights and aiming them down
• Use motion sensors and timers to insure lights are on only when needed
• Use the right amount of light, not too much, not too little
• In darker areas, use less light to prevent disrupting night vision

For a typical unshielded light fixture, 50% of the light shines upward. This is a direct waste and is the main cause of light pollution. About 40% of the light shines downward to illuminate the intended target. Light emitted horizontally tends to create glare, working against the productive light. A shielded fixture eliminates the upward light and minimizes glare, allowing a much smaller wattage bulb to be used.

The International Dark-Sky Association maintains a list of "Dark-Sky Approved" light fixtures and has comprehensive information on outdoor lighting.