Glowing glass / glass that can transport light?

[agentdark45]

Hi everyone, I'm in the early stages of working on a few concept renders of a hotel lobby for a client and the main feature is that there are several thousand glass rods that go through the ceiling of the building into the lobby, which will illuminate the interior with natural daylight (as well as the rods glowing from the outside of the building at night due to the internal artificial light being transported through the glass rods).

I'm having some trouble getting the glass rods to "glow" or transport the light without making them look matte (by messing with the glossiness parameter). At the moment they look far too transparent. I realise this is probably a nightmare scenario for any renderer...but any tips would be really really helpful! The glass material in the attached render is a standard one (ior 1.6 for both refl/refract, slow option not ticked).

The client wants this as a white render for now, which I assume will also make this tricky as there's not much to refract / reflect apart from a range of grey hues...

Many thanks

[Ondra]

Just fake the shit outta it in any way possible that will get you satisfactory results.

If you do not wish to fake it, you can try enabling caustics for the glass and praying ;)

Corona can simulate some cool stuff: https://forum.corona-renderer.com/index.php/topic,223.msg1588.html#msg1588, but it really depends on your scene configuration. You might even want to try bidir/VCM renderer

[agentdark45]

I had a feeling this was going to be a photoshop heavy project...I don't think experimenting with real caustics from 7000+ pieces of glass and nice GI would produce very friendly render times ;)

Thanks for the input though!

[romullus]

I tried to replicate light scattering in glass some time ago and find that use of little bit of translucency can help in that situation. Not sure if it could help you too, but it could be worth a try.

[agentdark45]

I had a go with tweaking the translucency settings but the glass ended up looking a bit frosted due to the number of rods. I'm sure I'll crack the perfect settings with more experimentation...

[maru]

Here is a quick test with caustics enabled and disabled. Without caustics the tubes don't cast shadows so it looks bad. Basically it is possible but I would try to fake it some way. Maybe don't make holes in the ceiling and put a CoronaLight inside the tube? Or change material of the top and bottom faces of the tube to CoronaLightMtl so that you can put custom colour on them?

[maru]

Looks like putting CoronaLights inside the tubes at the place where the tube meets the ceiling is a pretty efficient way but I can't imagine doing this with thousands of tubes on a curvy surface. Maybe with some scripting magic.

[Ludvik Koutny]

I would just put self illuminated material on the outer end of the tubes. I would use glass without caustics, and using rayswitch MTL, I would put some opaque material to base slot, so glass tubes would cast shadows. Then, i would put invisible rectangular light under the tube array. It is a fake, but it should be the best performing one.

Self illum material would make tubes glow, but it would not be explicitly sampled light source, so it would not generate noise

Glass without caustics would not make noise

Invisible rectangle would take care of efficient light source

The light distribution would probably not be same as with real simulation of this situation, but it would render quick :)

[agentdark45]

Awesome, thanks for all the tips guys! I'll do a few tests and report back...

[maru]

Rawa, the way you described it, you probably wouldn't get bright spots and the top visible end of the tube but this could be probably fixed some other way.

[Ludvik Koutny]

Rawa, the way you described it, you probably wouldn't get bright spots and the top visible end of the tube but this could be probably fixed some other way.

I have not tried, so i am not sure, but i would expect the refraction to transport that glowing part on the outer end to the inner end and create bright spot...  :)

[agentdark45]

OK so I'm trying out the rayswitch method and it seems that multi/sub-object materials aren't allowed (I get a red invalid material render). Would I have to manually disconnect the bottom surfaces of the cylinders and a assign the self illuminating rayswitch material to it?

I'm having a bit more luck with a planar light under the ceiling pointing down + a translucent glass like multi material with the end caps self illuminating (sorry for the small screenshot, the client doesn't want the design shown in full).