1 · Useful
Every light should have a clear purpose.
Try this: walk around after dark and ask of each light, "who is this for?" Switch off the ones with no answer.
A Practical Guide
Light where you need it, when you need it, and no more.
You don't have to live in the dark to see the stars. A few simple choices about fixtures, bulbs and switches keep outdoor light useful and give the night sky back.
From DarkSky International and the Illuminating Engineering Society
Every light should have a clear purpose.
Try this: walk around after dark and ask of each light, "who is this for?" Switch off the ones with no answer.
Fully shielded fixtures aimed down put light only where it is needed.
Try this: if you can see the bulb from the side, shield the fixture or replace it with a full cutoff design.
Use the lowest light level the task requires.
Try this: swap one bulb for a lower-lumen one and notice that you still see just fine, with less glare.
Light when it is needed, dim or off when it is not.
Try this: put the all-night porch or barn light on a motion sensor or a timer.
Limit blue-rich white light; choose warmer colors.
Try this: check the Kelvin number on the box. Choose 3000 K or lower, ideally 2700 K or amber.
Slide, switch and shield the lights of a whole mountain valley and watch the stars return.
Open the simulator →The single biggest difference most fixtures can make
Look for the number followed by "K" (Kelvin) on the bulb's box
Tick them off as you go. Your progress stays on this device.
A quick quiz with a score and your top three fixes.
Take the self-check →Try every principle on a whole valley and watch the stars return.
Open the simulator →Light pollution education and consulting with astronomer Stephan Martin.
About consulting →Quick answers
A fully shielded (or full cutoff) fixture is built so that no light shines above the horizontal: the bulb is hidden inside the housing and all of the light is directed downward. If you can see the bulb from the side, the fixture is not fully shielded.
Warm light. Look for 3000 K or lower on the package, ideally 2700 K, and amber light near forests, streams or other wildlife habitat. Blue-rich light of 4000 K and above scatters more in the atmosphere.
Safety comes from being able to see, not from maximum brightness. Glare from bare, bright lights makes it harder to see into the shadows around them, while shielded, well-aimed light at a moderate level, or motion-activated light, puts light where and when it is useful.
DarkSky Approved is a DarkSky International program that recognizes outdoor lighting products meeting its requirements for responsible lighting, such as full shielding and warm color. Its website lists approved products.