# Why is light visible? **URL:** \ **Category:** Factual Questions\ **Created:** [December 14, 1999, 4:36pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355 "1999-12-14T16:36:00Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [December 14, 1999, 4:36pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/1 "1999-12-14T16:36:00Z")
Specifically lasers. I think the question has come up before, but I don’t know that it was satisfactorally answered. To “see light,” the little photons have to be reflecting off something. What is that “something” with a laser? ---
**Author:** ![TomH](https://avatars.discourse-cdn.com/v4/letter/t/90db22/32.png) [@TomH](https://boards.straightdope.com/u/TomH)\ **Post date:** [December 14, 1999, 4:39pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/2 "1999-12-14T16:39:00Z")
I assume you’re referring to the beam itself. I think it’s tiny dust particles and so forth in the air. ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [December 14, 1999, 4:40pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/3 "1999-12-14T16:40:00Z")
Dust and water vapor in the air along the path of the beam. In space, lasers are invisible, Sci-Fi movies not withstanding. ---
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 14, 1999, 5:18pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/4 "1999-12-14T17:18:00Z")
The key is to have a bright highly focused beam, with a well defined ‘edge’. Bright searchlights are visible in air as well. The primary fluorescence is going to be water vapor (humidity) in most locations. Smoke, dust, rain, etc. can also help. Lasers aren’t always going to be visible. In extremely dry weather and without smoke or dust, you’ll only see the beam if it strikes a cloud, or some other object. * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 15, 1999, 1:14pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/5 "1999-12-15T13:14:00Z")
For that matter, it’s pretty hard to see laser beams in air unless it’s very dark and/or the air is dirty (fog, smoke, dust, etc.) There are some applications that use beams strong enough to be seen without turning off the room lights, but I haven’t seen any myself. ---
**Author:** ![Cooper](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Cooper](https://boards.straightdope.com/u/Cooper)\ **Post date:** [December 15, 1999, 3:41pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/6 "1999-12-15T15:41:00Z")
Whenever they wanted to show us lasers on the educational science programs on TV when I was a kid they would always have a fog machine going so you could see it. I was disappointed - I wanted it to be like a star wars blaster. ---
**Author:** ![Nickrz](https://avatars.discourse-cdn.com/v4/letter/n/bbce88/32.png) [@Nickrz](https://boards.straightdope.com/u/Nickrz)\ **Post date:** [December 15, 1999, 3:43pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/7 "1999-12-15T15:43:00Z")
**Caution - Do not look directly into laser with remaining good eye** ---
**Author:** ![Vestal\_Blue](https://avatars.discourse-cdn.com/v4/letter/v/5e9695/32.png) [@Vestal\_Blue](https://boards.straightdope.com/u/Vestal_Blue)\ **Post date:** [December 15, 1999, 9:30pm UTC](https://boards.straightdope.com/t/why-is-light-visible/5355/8 "1999-12-15T21:30:00Z")
More of the same: Laser pointers only show the red dot when it hits something, and they are to weak to interact with normal atmospheric effects. Somewhat fun in the fog, however. * * * VB “Hey! How 'bout that Toe Jam?”