Hi!

Does the type of light control how Photons are emitted? For example, if you have a cone light, are all of the photons emitted only inside the Cone?

If so, what controls exactly where the photons are emitted in the Cone- the “Cone Angle” or the Viewing Frustrum (Focal Length/Aperture) of the Light (and why aren't they related)?

Thanks,
Craig

Hi Craig,

You're right; IIRC, Mark told me once that the light shader is analysed and photons are only cast in regions that there is light. So the distribution of the photons are controlled by the shader itself only, not the View of the Light (fov,etc)

I didn't put a Light Shader on it, so I assume the default shader understands the Light “Cone Angle” and that is where the photons go?


Thanks,
-Craig

If you don't have a light shader applied Houdini will attach a VEX ASAD Light for you. (And correctly translate the cone angle parameters)

But as Peter Bowmar states in the other thread- are the Photons only cast in the Cone, or are still they cast everywhere, but given 0 energy outside the cone (and thus wasting a lot of the photons requested)?

-Craig

The idea of photons is that they're a packet of energy. The amount of energy does not vary per packet - so this means no photons are cast outside the cone.

Hope this helps,
Jason


EDIT: I've just read the other post - but I'm not sure that there are zero-energy photons cast. At least, in my memory I don't remember that; but its VERY easy to test. Use i3dconvert to convert the photon .pmap file into a .bgeo and take a look at the distribution.