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From left to right: Normal emitter, Hidden emitter (cast shadow) and Invisible emitter (cast no shadow)
The material for an Doing this is easy by following these two steps (one in the emitter material and one in the object itself):
- On the material for the emitter to be invisible
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- , aside from the emitting component
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- , add one single BSDF that must be set with Transmittance pure white (255) and Nd=1
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- .0 (which is the recipe for the vacuum or air).
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- This completely transparent and non-refractive BSDF corresponds to an "air" material, also known as "ghost" material,
- Then just enable the Hide to Camera option on the emitter object visibility options (and additionally you can hide it also from reflections and refractions it you don't want to see it reflected on other specular objects)
and your emitter will be completely invisible and cast no shadow.
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