Light and the Inverse Square Law

By Michael Johnson

So I’ve debated posting this for a while because I’m not a firearms expert (not even close), but I wanted to share some knowledge that I do have that I don’t think most people understand. I work as a photographer and thus my expertise is in light and working with light.

With that intro, I’ve seen a fair amount of resistance and misunderstanding about lumens and light and how far it reaches and how bright it is. There is a physics concept call the Inverse Square Law. In a nutshell, the Inverse Square Law says that if you double your distance from light source to target, you’ll only get 25% of the light reaching your target that you had before. Not 50% like you may think. Double your distance quarter your amount of light. So going from 300 lumens to 600 lumens will only give you an extra 25% reach, it won’t double your reach. Twice as far doesn’t mean half the light, it means a quarter the light. Thus all these people running around saying ‘all the lumens’. Light falls off fast, really fast. So take as much as you can get.

Richard Sandstrom pointed out “Also the inverse square law is an ideal, assuming a vacuum, therefore it is an upper bound. with air, dust, interference from other energy sources, etc performance will be degraded further.”

#allthelumens