Hi;

- I create a material called "Constant1" and I assigned it to material slot of a Geometry and an Areal Light in my scene.

- My geometry has an attributes called "MyParam“.
- I control some parameters in ”Constant1“, using ”MyParam“ attribute.
- The problem is ”MyParam" just makes changes to material assigned to the geometry , and the light's material does not changes.

I can not find any way to change parameters of that material in my Area Light's material.


Thanks.
MSD.

- I think Houdini makes a instantiate of that material for each item, right?

How could I override material parameters, assigned to “Material slot” of an area-light?

Lights do not use materials. Lights use light shaders and shadow shaders. The outputs and inputs of which are different than that of a surface shader. If you want something simple such as the position on the surface of the light driving a pattern that controls intensity, this can be achieved. However you will need to re-implement the other functions that you may have been using on the built-in light shader if starting from a blank slate light shader builder node. Take a look at the source code for the v_asadlight shop. Attributes on your geometry won't be available in the light shader anyways, unless you are creating a geometry light, in which case, the surface shader is used by the light. Are you trying to create a geometry light (mesh light)?