Am 06.04.2018 um 17:54 schrieb IGM:
> Hi,
> I would like to render realistically a "diffusor sheet", like for example this:
> https://www.inventables.com/technologies/light-diffuser-films
> 
> In povray, if I create a scattering media thin box, thanks to scattering media
> the sheet becomes increasingly white, but I still see a light source, behind the
> sheet, sharply defined. In other word, I need to obtain a blurred source behind
> the sheet.

You can model an ideal diffuser sheet using a patch primitive (such as a
triangle, an open mesh or a bezier patch*), and using the two-value
`diffuse` syntax, aka backside illumination, like so:

    texture {
      ...
      finish {
        diffuse albedo 0.6, 0.3
      }
    }

(*Alternatively, you could also cut out a piece of surface from a solid
object, such as a sphere or cylinder, using `clipped_by`.)

This tells POV-Ray that from all the light shining onto the surface of
the object, 60% should be reflected in a lambertian manner, i.e.
independent of the incident light angle and with a cos-law distribution,
while another 30% should be emitted on the other side, also independent
of the incident light angle and with a cos-law distribution.


Of course real-life diffuser sheets aren't ideal, as transmitted light
/is/ dependent on incident light angle, so if you need to model the
material more precisely, in its current form the backside illumination
is probably of little use to you.

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