[designer-made]

Trying the render a chandelier with emitters, but am just getting noise, caustics and extremely slow render times.

The geometry matches an actual prototype I've got in front of me. Each lighting element consist of a single, small (say 1cm sphere) 35w halogen bulb inside and at the bottom of a 12mm thick, clear wavy glass (various bubbles, ripples) cylinder (about 6.5cm diameter x 15cm high) open at the top. In reality the bulb appears like a bright, distorted sphere inside the cylinder (due to refraction) and the light effectively illuminates the entire cylinder, such that the glass itself behaves like an emitter.

What would be the best way to recreate this effect in maxwell?

I've read numerous posts about the problems of placing emitters behind glass, but I can't figure out another way to get realistic results in this case. Is there a consensus on best practices for emitters and glass, besides "don't do it"?

Many, many thanks in advance.

Cheers

[eric nixon]

screenshot? or a reference photo, would be good here...

[Mihai]

Try adding an emitter component to the glass material itself.

[choo-chee]

try to photograph the actual light source and make it an mxi emitter.
map it to the glass object itself.

[eric nixon]

It is actually possible, (but very slow), to put the emitter inside the glass volume;



Inside a simple volume is faster, this is ok for feature lighting, not for illuminating the whole scene.. that would be v. slow..



It looks nice, but its a volume of glass, not a shell....

[bograt]

Eric were those your renders? you always seem to have very relevant example renders at hand... I like the bird glass btw

[eric nixon]

Every situation in the universe has already been tested and catalogued by the Borg....

[designer-made]

Thanks for the tips and awesome samples. Just what I'm after.

Eric, if you wouldn't mind sharing your secrets, can you explain the basic setup of the glass objects in each of the renders shown. I'm brand new to MW and don't quite understand how you achieved these effects. I assume the glass objects are solid in both examples. Are emitters applied to the glass objects themselves? If so, how did you incorporate the bird motif? Is the bird lamp lighting the wall, or is there some other trick? I couldn't seem to get any light to really escape the glass in my experiment.

When I get back to my work machine later, I'll post a pic of the render I did the other day. BTW I had to use like a ridiculous 100000w halogen to begin to fill the glass with light, and the scene itself was still dark and very noisy.

I'll try applying the emitter (either standard or photo) to the glass and see how it goes. If it is still slow, hopefully, I can still get a decent effect with a simpler, less distorted glass material.

Many thanks again.

Cheers,
andrew...

[eric nixon]

Hi I missed your reply. As far as i remember there are no tricks here, the glass has roughness 0 - that matters, then the emitter is inside the glass volume. Thats all.

[designer-made]

I've been messing around with this for past several days and finally got a result I'm not embarrassed to post. What's shown here is just under 22 SLs.

Following Eric's advice I made the glass cylinders solid and embedded a 60w spherical emitter inside each toward the bottom. The glass itself is a low-grade glass with a tweaked displacement map I found inside of another wavy glass from the mxm gallery. I also added a very low power emitter to the glass itself as well, like 3w, to make it glow a bit more. More than that and it seemed to get really noisy.

The biggest problem was waiting for the many SLs to clear to see if the result would work. That displaced glass does not begin to show its true luminosity until well into the process, and my quad core i7 is feeling really slow. I also had to change my composition a bit too, because some speckly noise from the the lights in the background was showing in front of the chandelier arms in front of them. That may have cleared itself up with more SLs, but I didn't want to waist the processor time, so I just rotated the view so that the lights would not be obscured by the arms.

In reality the glass glows a lot brighter, but just bumping up the wattage of the emitters seems to get noisy quick. Anyone got an idea for how to get them more luminous, but clean?

Many thanks again for all the help.

Cheers,

[Bubbaloo]

If you have enough RAM, try switching to Pretessellated displacement for the glass if you are using On the Fly. It will render faster. (or model the glass pieces instead of displacing them). An emitter inside a displaced glass object is very tough to get clean. Also, try turning on MultiLight so you can adjust the intensities later.

[eric nixon]

I had a closer look at this, I found in my old chandelier render it had some sss which gives it a cloudy look which isnt good. It seems surprising that you CAN put an emitter inside a object with a little sss.

I also found that if the emitter is inside, the caustics are not working right;

outside; inside;

So basically I dont know how to make the glass glow, its prob related to infinite internal reflections which maxwell cant calculate...

[JDHill]

When you put your emitter geometry directly inside the glass volume, you create a situation in which you skip a critical emitter -> glass junction. You would need to enclose the emitter in a bubble with correctly-facing (to the inside) normals. The bubble should be a part of the (now discontinuous) glass mesh, such that you obtain a correct emitter -> space -> glass (in) -> glass (out) -> table surface path. The space around the emitter geometry is necessary because it would be indeterminate, given coplanar emitter/glass faces, which would be found to be nearer to the outer glass surface.

[eric nixon]

Yes good point,... I did that version but didnt save it, caustics are good but glass still doesnt 'glow'...

EDIT found it in the cache, has sss and dispersion;



The best workaround is using higher nd and a shape that encourages reflections of the emitter, ie not a parallel cylinder, but its not really the right look.

[designer-made]

Thanks for the additional insight and examples. Really helpful.

Regarding the bubble-around-emitter approach, is there any rule of thumb for how to determine the spacing to use between the emitter and glass? I ask because my first attempt was to simply put the emitter inside of a glass cylinder--a bubble of sorts--but that did not work very well. In that case the spacing was something like 1cm or so.

Cheers,