Shadows Don't Make Sense

I think what you're observing there would be the effect of diffusion. In a reflective environment, light, even that from a point source, falls upon the object illuminated not only from the primary light source, but from all the reflective surfaces of the surrounding environment - and any surface not an absolute, full-visible-spectrum-absorbing, flat black surface is a reflective surface; if you can see it, its reflecting light. Its a principle well understood and widely exploited in photography.

That's not diffusion.

Anyway, this problem was blatantly obvious I dont know why I didnt realize this...it's because there aren't many photons that come in between the two shadow casting objects, and the same photons cant be occluded twice

I think I understand where you're coming from, but maybe not. Call me stubborn, but I still think I'm on the right track. What forms the basis for my conjecture is a photographic discipline known as the Zone System, particularly as applied to photography with complex multiple light, reflector, and diffuser rigs.

Now, in your "Expected/Observed" example, what I see is that the larger object casts a shadow of a given density. The smaller object casts an overlapping shadow, of lesser density. The behavior exhibited in the lower frame is precisely what I would expect.

But then mebbe I'm way off base - I'm shooting in the dark here :wink:

Tricky puppy you are, eh? Pulled that example right out from under me while I was composing

Anyhow, from what you said, it appears to me we're more or less in agreement as to what was going on

Yeah I pulled that example out because I realized I was just being stupid!

Or was that just a shadow of your idea being presented?

Interesting stuff. I want to start studying light and light dynamics but alas, no time. But this was a cool read. Thanks for bringing it up.

Er shadows are just the absence of light, how can light be more absent than absent?

Have one light source, say a candle and block the light source with a hand - you get a shadow. Block it with two hands and you don't get a darker shadow. The light isn't any more absent.

If you have 2+ light sources you have to calculate you lightscource illumination map using all four light sources (diffuse, ambient, emmisive and spectular are markedly different and you must especially take into account radiosity of indirect lighting).

A great explanation is here:

http://www.beyond3d.com/articles/vs/index.php?p=4

BTW

With 6 light sources (downlights) in my kitchen I was able to get a darker shadow in the intersection of two light sources last night - froma chair and an open cabinet door - the intersection point of the two shadows was much darker than their individual shadows.

So it depends on how the light is getting to your obstructions that determines what dhadows you will see.

block a shadow with 2 hands, and it will be darker than blocking with just one hand, because of the indirect light that is additionally being blocked. the confusion originally came for me because in the situations where I was observing this, I thought that there was a lot more indirect light than there actually was, because there were large distances between the objects.

I still find it quite amazing that shadows in real life can be so uniform. It is very common that we see an indoor room with a small light source that seems to almost uniformly lighten everything in the room. Attempting to recreate this effect using computer simulations usually requires faking it, because usually in order to get light reaching into the corners etc requires letting in a lot of light and letting it bounce around a lot, which ends up with much more contrast than is evidenced in real life.

I think that this phenomena in real life is probably due to the bumpiness of surfaces which causes them to scatter light in a much more even way than the perfectly smooth surfaces in my simulation