Let's say that I have a detector and a few sources of light (think lightbulbs). The sources are all the same power and emit different colours of light. We're on the surface of Earth.

As I walk further and further away from any given source, the detected intensity will drop off. I believe that the intensity of longer-wavelength light will drop off more slowly: longer-wavelength light experiences less scattering and absorption. How do you mathematically categorize the relationship between change in intensity over distance (specifically with respect to scattering and absorption in air) and wavelength?

I'm particularly interested in how far below the visible spectrum you need to go before you see appreciable/significant differences between a visible source and an infrared source.

  • $\begingroup$ Are you referring to light scattering in air or generally, in a vaccum? $\endgroup$
    – Zac67
    Mar 15, 2022 at 19:26
  • $\begingroup$ Specifically in air. (Question updated.) $\endgroup$ Mar 15, 2022 at 19:29
  • $\begingroup$ Since we’re talking about lightbulbs, are you aware of the inverse square law? $\endgroup$
    – Gilbert
    Mar 16, 2022 at 3:03
  • $\begingroup$ In the sense that the intensity of light, generally, falls off with 1/r^2? Yes. If you mean some other inverse square law that applies instead to wavelength, no. $\endgroup$ Mar 17, 2022 at 16:14


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