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SESK: Stuff Everyone Should Know · sesk.info/astro-red-light-night-vision

Which flashlight color best preserves an astronomer's dark adaptation?

Use a very dim red light.

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  1. Bright blue
  2. Dim red ✔
  3. Bright white

Why: Red light has less effect on dark-adapted vision than white light. It should still be kept as dim as practical.

Huh, didn't know that: A red screen setting can make a phone less disruptive at an observing site.

The dad joke
Astronomers use red lights so their night vision does not see red.
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References

Answer: Dim red. Red light has less effect on dark-adapted vision than white light. It should still be kept as dim as practical.

  1. How to Find Good Places to Stargaze science.nasa.gov/solar-system/how-to-find-good-places-to-stargaze
    red light has the smallest impact on your night vision
    Checked 2026-10-10.

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