Translucent - light not passing through

I am trying to essentially re-create this material

Taken from:

I cannot get light to pass through the material though. A few searches showed this has come up before, and I have made sure I have high passes for transmission and transparency, and also have caustics on (I hope I have done this right?)

I have a simple sphere with a white emission material with a strength of 999,999; it is placed inside a round object (round ceiling fitting)

And the result is that the translucent parts lights up, but no light comes out onto the surfaces around it. Could anyone tell me what I am doing wrong? I am relatively new to cycles. Thanks for reading

Given how brought your light source is - you probably wont be able to tell the difference between the translucent and emission material anyway.

I just rendered a similar scene to yours (100 samples). The first is set up like yours with a small emission sphere hidden behind a translucent/glass cover.

The second has the cover emit the light itself. As you can see - the light cover itself is so over exposed you cant tell which material it has applied. It makes a huge difference to the noise though.

You could try to replicate this material

very little light pass through transluscent mat

instead use glass with some roughness

happy cl

It wont help. Path tracers don’t deal with lighting through glass very well as you are essentially lighting the scene with caustics.

This is a screenshot of glass with roughness - and it still suffers from excessive noise.

One trick you could use OP is the lighpath node.

Essentially this setup makes the shade invisible to the light - allowing the light out into the scene - but makes the shade visible to the camera. Still a bit noisy due to the size of the mesh light - but it’s better than lighting through translucent.

main problem is we don’t have glow material yet in cycles !
when are we going to have this effect in cycles ?

mind you
you can always do it in Bl then composite it with cycles

but very difficult to do in cycles right now

so do it in pure BL and it is easy to do or
may be try it in Yafaray or Lux might work better

did a quick test and difficult to get anything like in BL

found this one

happy cl


Not sure how a glow material would help in this situation. The OPs problem stems from the fact that the path tracer is trying to find a small light source through a refractive/translucent material (one of the worst combinations for a path tracer) - it’s not down to ‘glow’ or lack thereof.

Also - glow effects aren’t really a material property. In the real world - the glow that is often observed around bright light sources is due to either atmospheric conditions like dust/fog or lens defects inthe eye or camera - both of which can be simulated using volumetrics or compositor.

there is some glow inside the shade from lamp
but also some halo around the shade and have not seen this in cycles yet!

if you have a trick to do it let us know!

and volume might be able to do some halo but a lot more complicated to do

and agreed that glow halo are supposed to be part of composite
but in Bl we also have it in material spec which is way faster and easier to use
so would be nice to have equivalent in cycles

happy cl

Are you talking about the lamp in the top post? It was rendered in cycles - so if there is a glow it’s likely to have been done in compositor.

Since the OP is also using cycles - they can use exactly the same method.

Of course - unless they sort out the lighting issue - it’s all academic. Adding glow to a scene that isn’t lit properly would be pointless.

yes I was talking about the first post image

which looks good but still far from a realist physical render
it is way too bright

would be nice if OP would upload that file so we can look at it

center of lamp looks like glowing but could simply be a very bright lamp
also lot’s of wall reflections which looks like halo but it is not !

happy cl

Hi, first off, I am taken aback by the number of detailed replies, thank you all for your help.

What I set out to achieve was a light of this style
Though I wanted it to dimly light my scene.

On my first attempt the glass cover part of the light was an emission material, but it seemed so bright and unnatural to me (am I wrong about this?)

I then remembered reading many times about try to create it as in real life for cycles, so stuck it behind a glass cover
Which I like if not for the problem of no light getting out (there is a separate light to the side lighting the casing in this pic). This was with 40 or so strength for the emission sphere material.

In frustration I ended increasing the light spheres emission strength to the point where it does indeed look no different to just using plain emission.

The setup from the youtube link eppo provided has given me the best result so far I think

moony your lightpath node gave a pretty similar result to the above aswell, just a bit more noise though I think thats because the above was with a pointlight.

Hoping to avoid going back to Internal tbh, seems like a lot of work and I have a large number of shots of the same scene from different angles I wanted to do.

Not entirely sure what I’ll go with, lights that are actually visible in the scene and are not just a window or a sky texture are what I have struggled with most in cycles, not many tutorials cover them - it’s always a emission plane out of view.

If you want your cover to emit a lot of light - but not appear as bright and over saturated - try the following node group on it:

This way your cover still looks like it is emitting - but also retains some glossy reflections - but it emits a lot of light into your scene. You can control the light output into the scene and the light output of the shade independently. Best of both worlds.


There is something wrong somewhere. This is what i get from one light emitter - pointlight covered by Negativa’s fast translucent shader group shade:
Pay attention to sample count. To be honest, walls have some bit of AO added.
Your copied node group starts with Diffuse/Translucent mix; Diffuse clearly is not what you want light to pass through, it just does not makes sense. Try glass instead. Also other parts in Negativa’s shader group make render faster and eliminate noise/fireflies - do not ignore that.

Damnit… embarrassing. You are right eppo, I had made a mistake. I had added thickness to my glass cover and forgotten, once it was single polys the light made it through nicely enough. I have actually gone back to blender internal now though.

Thank you for all your help everyone.