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Understanding Outdoor Lighting

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

Outdoor lighting is certainly something we need. It provides safety from crime, visibility on roadways, and comfort when walking at night. But more and more lights are being used improperly and with little thought to address human needs and the effect upon night sky quality.

When you can see a light from far away or from above, it is probably a bad light. Poor quality outdoor lights do more than just spoil the view of the stars: they can confuse and harm wildlife, cause 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. There is also growing concern that nighttime lighting can adversely affect human health (International Dark-Sky Association, 2009).

What Makes a Light Beneficial?

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 a neighbor's window. Good lighting incorporates modern, high performance optics that aim light in a defined pattern to reduce glare and light pollution.

Energy Efficiency

Night sky friendly lighting can go hand in hand with energy-efficient lighting. In fact, far more energy can be saved by employing night sky friendly principles than by simply using a more efficient light bulb. Likewise, just making a light more energy efficient does not necessarily make it night sky friendly.

Light Emitting Diode (LED) lighting is rapidly becoming popular and has many potential benefits. LED lighting can be easily dimmed and linked to smart controls. For example, the lights may brighten as you approach and dim as you pass on by. LEDs can also be precisely aimed, resulting in less glare and better visibility. However, the appeal of LED lighting would be harmful to the environment if it resulted in many unnecessary lights being installed outdoors. Additionally, LED lights that are rich in blue light (cool-white LEDs or those with a color temperature greater than about 3500 degrees Kelvin) can result in greater impact to starry skies and ecosystems (International Dark-Sky Association, 2010).

Principles of Night Sky Friendly Lighting

  • Use outdoor lights only where you need it.
  • Use light only when you need it by using timers, motion sensors, and advanced controls.
  • Shield lights so that all light is directed downward, below the horizon.
  • Use lamps with warmer colors; avoid cool-white lights.
  • Use the minimum amount of light necessary for the task.
  • Use the most energy-efficient lamp and light fixture.


International Dark-Sky Association. Light Pollution and Human Health. 2009.

International Dark-Sky Association. Visibility, Environmental, and Astronomical Issues Associated with Blue-Rich White Outdoor Lighting. 2010.

Last Updated: April 23, 2012