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I'm trying to make a mesh light that's invisible. It's supposed to light the inside of a cylinder.

But setting the opacity to zero causes the emittance to also go away.

Am I missing something?

So, 20 people saw this question, and nobody knows the answer.

Phew. I had first been worried that I'm just missing something really basic.

Tried again today to get my emitter mesh to disappear by setting opacity to zero, but it only works in the material view. As soon as I hook up the node to my obj mesh and view the scene, the light goes away.

Sigh. Anyone with ideas, would love to hear them.

Thanks.

Hey, thank you so much for the very detailed answer.

You know how in some biased renderers, you can add a point light somewhere, and it will help illuminate otherwise dark areas?

I'm trying to do the same thing, basically.


One thing I don't understand is surface illumination, regardless of whether I switch it on or off, the light effect looks identical to me. What's the difference?

I do want to retain the reflections of the light.

My scene is simple: a cylinder with a very glossy surface and a bump map, and a plane nearby with an emittance, sort of like a studio spot light. The result is that the inside of the cylinder is very dark. I want to light that up a bit to bring out the bump map.

My solution was to place a small plane right above the cylinder opening, but of course I just want the light effects (illumination and reflection) and don't want to see the geometry.

The render passes idea sounds intriguing. And what did you mean when you said something about hiding the geometry, without setting it to opacity zero?

Thanks again.

Thanks again for your helpful and detailed reply.

Turns out render passes don't work either. The emitter mesh acts like a mask, removing anything behind it.

Looks like what I'm trying to do is not how physical renderers are meant to be used, since I'm technically going for an "unrealistic" effect.

I sure wish mesh opacity would be independent of its light emission. In my mind, the emission power setting controls the light, not the mesh.