Sunlight decay test

[JeffG2]

I recently ran a quick Vray test to see if sunlight decays on it's bounce.

The results are not what I expected.

I cleared a shoebox shape - roughly 1ft. wide and 3 ft. tall - then scaled it up to 30, 300, 3,000 & 10,500 ft. tall. I gave all surfaces a generic, grey VRayMtl. I moved them around so they sort of lined up.

I was expecting that the quality of the light and shadows in the various boxes would be quite different - especially that there would be practically no light reaching the upper inner recesses of the 10,500 ft. tall box. I was very surprised to find them all very much the same. Photoshop's color picker spot checks showed them to be almost exactly the same.

Am I expecting the wrong results here or is Vray not accounting for some property of sunlight? Perhaps the lack of decay is due to not accounting for the effects of atmosphere on the sunlight bounce?

I used:
Primary Bounce: IR map (1.0 mult)
Secondary Bounce: LC (0.8 mult)

[Aldaryn]

Consider, that the directly illuminated area where a big portion of the bounced light inside the boxes comes from increases quadratically with your scale, so this seems to be the accurate result.

In reality, some other factors may affect light that's currently not simulated in Vray, or example, put some haze inside with real world scale, and your tall boxes will immediately look like big objects, not to mention that air itself absorbs light, so it souled be considered as a participating medium, and it even scatters some. (hence your skylight...)

Best regards,

A.

[Morbid Angel]

Consider, that the directly illuminated area where a big portion of the bounced light inside the boxes comes from increases quadratically with your scale, so this seems to be the accurate result.

In reality, some other factors may affect light that's currently not simulated in Vray, or example, put some haze inside with real world scale, and your tall boxes will immediately look like big objects, not to mention that air itself absorbs light, so it souled be considered as a participating medium, and it even scatters some. (hence your skylight...)

Best regards,

A.

correct. Also that they are situated on one large plane, which uniformly and infinitely bounces the light, so it becomes relative.

[vlado]

The result that V-Ray produces is correct. You are changing not only the height of the boxes, but their width as well, so even though the light decays with the inverse square of the distances, you are also changing the area of the light-bouncing surfaces. Both of these cancel each other out to produce the same lighting disribution in the end.

Best regards,
Vlado

[JeffG2]

Well, this has been a very illuminating experience!