I came across a problem with emitting light through Glass in Cycles - a police siren - No matter what Emission value I set, it stays this dim.


Glass BSDF
IOR: 1.450
Roughness: 0.0

Basically setting any value higher than 1000 has no effect

I tried lowering the IOR of glass, mixing with transparent node, that however created very strange, burned, overexposed effect with the light being pink.

P.S. I want to avoid multiple Render layers, though for now it seems like the only option, or even if possible at all.

I would love to achieve this effect:


Thanks for any help!

  • $\begingroup$ did u try glare node? $\endgroup$
    – Chris
    Commented Oct 23, 2022 at 10:23
  • $\begingroup$ I'm wondering like @Chris if you tried compositing or do you expect it to glow just by increasing the strength? These glows and lens flares etc. which you see in real photographs are usually an effect of overblown light sensors in cameras, lens imperfections and don'T let me get too technical here, but a virtual camera in 3D software doesn't have this. All is rendered crisp and clear until you go and create something like glow effects in compositing. Also things like depth of field or motion blur do not happen naturally with virtual cameras unless you tell them to calculate such things. $\endgroup$ Commented Oct 23, 2022 at 12:28
  • $\begingroup$ For the light getting pink, well that depeds on what basic color you have set for the light. For example if you have RGB (1, 0, 0) than it will mostly stay completely red, since green and blue are not present and multiplying with some strength doesn't increase them (if Color Management is set to Standard, but Filmic might change these base values). If however your green and blue values are > 0, then they will change the color the higher the emission strength is. A higher blue will make it pink, a higher green will make it orange. Until the strength is so high that it gets all white. $\endgroup$ Commented Oct 23, 2022 at 12:35
  • $\begingroup$ I found the problem to be in the Glass shader itself - since it did not pass enough light, it was not the problem of Emission being pink (the RGB node was full red). When I adjusted the glass (for a more realistic one also) node, the light was way more bright, able to be composited later on also. Hope my last post explains... Thanks guys anyway for digging into it, appretiate it! ;) $\endgroup$
    – Jan Hrodek
    Commented Oct 24, 2022 at 8:32

2 Answers 2


try this nodes setup in compositing:

enter image description here


enter image description here

  • $\begingroup$ Thank you for the suggestion! ;) $\endgroup$
    – Jan Hrodek
    Commented Oct 24, 2022 at 8:26

Thanks for the suggestion with glare, however the problem was with the Glass. Just in case of anyone interested I am posting my solution:

I brewed this material for the transparent cover of the siren, that allows to pass way more light from the emission

Glass material

Glass before:

Glass BSDF only

Glass after:

Glass composed

I played with the compositing also to get control over the Glare effect, since it created strong outlines on default value:


This is the final result I am satisfied with (I did not go for the full light effect at the end)

Final result


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