Control Emission Angle Using Nodes for the Emission Shader

Hello All,

I have a question about the emission node. I need to make a light that emits preferentially to one direction. I want to be able to control the emission angle from the light.

For example. If I have a flat circle and set the material to an emission material, I want to be able to control the angle mathematically. I want a cosine squared distribution (or potentially cosine cubed). So if I put a hemisphere over the light it should be very bright tangent to the plane of the emitter, and it should be dark in every direction parallel to the plane.

Is this possible?



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sounds possible with the math nodes I think.
maybe somebody with more math skills and how to do that vector manipulation could help here?

Yes it’s possible, you can get use the Vector Math node to get the dot product of the normal and incoming vectors (which are outputs in the Geometry node) and then map the greyscale data from the ‘dot’ output through a color-ramp.

You then use a math node to multiply it to the desired emission power and multiply it by the output of the geometry node’s ‘backfacing’ output (which will eliminate light coming from the direction opposite where the normal is facing).

Cheers Ace Dragon, had a play with this and got some interesting results. After changing things up a bit, here’s what I settled with:

Colour Ramp adjusts the “focus”, back facing subtracted out, Colour is adjusted with a colour mix multiply, strength and fall off type controlled with the Light Falloff.

Switching up the colour mix mode can have some interesting effects too.

I don’t fully comprehend all the nodes, but this certainly seems to be doing the job for me. Thanks for getting me there :smiley: