I am sure it's just your eyelashes creating a filtering effects, but if you look a a bright(ish) light source such as a lightbulb while squinting, if looks like you are seeing straight light rays emitting from the lightbulb, I assume you can't see an individual ray of light like this?

Question

I am sure it&#039;s just your eyelashes creating a filtering effects, but if you look a a bright(ish) light source such as a lightbulb while squinting, if looks like you are seeing straight light rays emitting from the lightbulb, I assume you can&#039;t see an individual ray of light like this?

Jake Landry · Accepted Answer

As is obvious from women&#039;s hair-dying commercials, human hair has a small degree of reflective sheen to it, and so when you squint, it seems plausible that as the eyelashes intermesh over each other, some light which otherwise would not enter your pupil will strike your eyelashes, be reflected, and enter your eyes from a different angle than the original light source.One simple way to model this is to model the eyelash mesh as a semi-transparent isotropic diffusive scattering surface with absorption. An ideal example of this would be a thin sheet of plastic with absorbing dye and scattering       TiO    2   particles dispersed throughout it.In this model, a fraction T&amp;lt;1 of the light is transmitted without any collision or angular deviation, a fraction A is absorbed by the eyelashes, and a fraction S is scattered isotropically from the scattering plane, with  T  +  A  +  S  =  1For concreteness, let the YZ-plane be the scattering surface, let the eye (modeled as a tiny square of area α in the YZ plane) be located at (−d,0,0) and put a point source of light at (r,0,0) with emission intensity       I        r    2   per steradian (so that the light intensity remains constant regardless of distance r). Then from the light due to the point source which passes through without being absorbed or scattered, the eye receives an amount of light      P    source    =  T      I        r    2        α          (      r      +      d              )        2              →  T      I    αin the limit   r  →  ∞ (ie, as the point source is moved to infinity but its apparent brightness is kept constant).Meanwhile, a patch of diffusing surface located at (0,y,z) with unit area will receive an amount of light      I        r    2        r                  (                  r          2                +                  y          2                +                  z          2                )                    3                  /                2              →      I  which will then be isotropically reradiated with intensity             S              I                    4      π       per steradian. From this, the eye will detect an amount      P    diffuse    =  α            S              I                    4      π            d                  (                  d          2                +                  y          2                +                  z          2                )                    3                  /                2              .Now all that remains is to convert these to solid angle intensities as detected by the eye. For the diffuse light, note that when looking at the point (0,y,z) on the diffusing panel, a solid angle dΩ looks at a patch of area  a  =  4  π  d  Ω                    (                  d          2                +                  y          2                +                  z          2                )                    3                  /                2              d

I am sure it's just your eyelashes creating a filtering effects, but if you look a a bright(ish) light source such as a lightbulb while squinting, if looks like you are seeing straight light rays emitting from the lightbulb, I assume you can't see an individual ray of light like this?

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