I am just completely lost.

Question Lighting

Hello, I love the idea of learning lighting in blender 3d, but i just cant D:
So far in this course I fear I understood very little of light.

I see it like this, in school they taught us the basic way to multiply multi digit numbers, but not the place value meaning, so it left us with this way to multiply and get the right answer, but not understanding the "how" it worked.

I feel the same way with the lighting in blender 3d, so many values and just feels like guess work, and even then after what we see it feels like blender is doing stuff we don't see.


Like in this image, its just 1 diffuse light bounce with 1 max bounce total, very simple, however there's lots of...things going on.
Its a sun lamp and you see the main angle of it, pointing down from the top right side.
However, with just 1 bounce of light...it hits the red wall, and given the angle it's next bounce will aim it to the floor or somewhere on the cubes, done, that's 1 bounce.

But...see the red on the ceiling? Given the angle of this light...it feels truly impossible for the red to reflect up there with 1 single bounce, I just cant see it happening

Then the arrows, they point to odd lines of shadow I just cant find the meaning of, they are there from nothing.

I just wish I could visualize the path of these lights but is that possible?
Could we make blender map out a few of these points of light?

  • wardred replied

    If I'm not mistaken there's no "front wall" to your room.  It looks like the sun is pointed down and to the left.

    The top shadow would be from the ceiling, and the one on the right from the wall on the right.  Sun lights are a little tricky as it doesn't really matter where they're placed, 

    The red is mostly bouncing off of the column, I believe.  Also, if the surface has roughness and or diffuse to it, some of that is going to bounce up.  Think of rough paint instead of glossy.  Some of the geometry is going to bounce light up instead of acting like a mirror and "perfectly" redirecting light.

    Sun lights can be a little tricky.  It doesn't matter where they're placed, only the direction they're shining.  Try rotating along the Z access to the right - clockwise.  You should get to a point where the shadows are coming from the wall on the left instead of the wall on the right.  You could also rotate up and down and have shadows coming off of the floor, if you wanted.

  • wardred replied

    I take it back about the column.  The diffuse red is directly from the wall.  The light is scattered somewhat randomly.

  • Martin Bergwerf replied

    Hi Jason,

    I can understand your confusion and it's a great point you make!

    The fact is, that Blender starts counting at zero; the first ray hits a surface and that is bounce 0. A possible path with total Bounces set to 1 is:


    So we have in order: Camera Ray > Bounce 0 > Diffuse Ray 0 > Bounce 1 > Diffuse Ray 1 > Light.

    After a Bounce, there are many directions the Diffuse Ray  can go, I just drew one possible path, that actually hits the light. The Rays that do not find a lightsource within the Bounce Limit, get ignored/ will not contribute to the lighting.

  • Omar Domenech replied

    Also don't think of it as a light ray doing all of that, from just one light source there's lots and lots of rays being produced from the camera an hitting that light, scattering and going all over the place, lots of them, it's just that they all bounce once and stop, but in that while before thy stop then can do a lot. So hopefully with that picture in mind it's easier to see how that final result is being produced. 

  • Jonathan Lampel replied
    But...see the red on the ceiling? Given the angle of this light...it feels truly impossible for the red to reflect up there with 1 single bounce

    Like Marin and Omar mentioned, a diffuse material will scatter light in all directions. So, even though the sun is hitting it at a very specific angle, some of it will end up on the ceiling after one bounce!