Uniform Hemi light

[nikosg]

Hello,

The problem: to get a light distribution that is uniformly distributed across a hemisphere. In other words, a point in space (the center of the hemisphere) receives light of equal intensity from all directions in a hemi around it.

:) Before someone jumps and says 'Hemi light', hemi's distribution is not actually uniform (maximum in the direction of the light, zero at the perpendicular). Or am I wrong here?

[stiv]

Hemi Light!

http://mediawiki.blender.org/index.php/Manual/PartV/Lamp_Types#Hemi_Light

[z3r0 d]

Before someone jumps and says 'Hemi light', hemi's distribution is not actually uniform (maximum in the direction of the light, zero at the perpendicular). Or am I wrong here?
I think you're wrong there

http://download.blender.org/documentation/htmlI/ch12s02.html#hemi_lamp

[nikosg]

Hi, thanks for the replies,

The manual says:
"Its dashed line represents the direction in which the maximum energy is radiated, that is the normal to the plane defining the cut of the hemisphere, pointing towards the dark side." (my emphasis)

As an experiment, I tried this: A hemi at (0,0,10) pointing down, a plane at (0,0,0) and a camera at (0,0,5) looking down. I turned on diffuse-only and rendered the attached image. If the energy is equal in all directions the plane should have a uniform highlight covering the whole of its surface, but it does not... Hmmmm

[grafix]

I can't seem to find the diffuse only button. Are you sure you didn't press the no diffuse button on the lamp instead? I can get uniform lighting with the hemi lamp at the position you specified. I had to turn on the No Specular button on the lamp, though, or the entire thing turns white...

[nikosg]

Yep, sorry, I meant "No diffuse" indeed. The problem with "No specular" is that specular reflections are exactly what I need :)

[grafix]

Not entirely sure about this, since I'm entirely self taught, and don't have a really deep understanding of the processes involved, but I seem to remember reading somewhere that specularity in 3d is a big fake. It's all round shaped, and the lights only control the specularity intensity and position...
You could try turning down the hardness of the specularity to 1 and mess around with the various types of specular shaders, though...

[z3r0 d]

Yep, sorry, I meant "No diffuse" indeed. The problem with "No specular" is that specular reflections are exactly what I need :)
well that's your problem

as long as your camera has perspective the specular highlights will be round, regardless of how uniform the light is

[it's easier to picture this in 2d]

[nikosg]

I think you are both right and I see now that what I am asking for is stupid!

If light was truly uniform then everything (regardless of orientation to the camera) will be entirely highlighted (as in: entirely flat), something which I don't want.

I've had a look at the source code and my guess is that a hemi is treated as a sun for specular reflections. So, maybe I can use a hemi for diffuse and that annoying icosphere of lamps for specular....