Caustics.. why are my object edges so dark?

[RRIS]

Hey all, without posting the content of what I'm working on, I'd like to explain my issue. I have a transparent polycarbonate box with some equipment inside. Now, because some of this stuff has lights in it, I need caustics.
However, the caustics take absolutely forever to clear up and most of the geometry inside gets darkened edges/corners on surfaces receiving caustics.
Is this normal and do I simply need to extend my render times? I'm rendering a test frame at the moment and at 1300 samples everything still looks like a sponge with darkened edges.
I guess it doesn't help that the parts inside are a shiny bright white plastic...

[RRIS]

Things I'm thinking of changing:

- exchanging white plastic (is it just me or is there some subtle sss in that shader?") materials for white paint and up the environment brightness (I'm using max. 85% gray on all white surfaces from the start).

- change the area light I'm using inside the box for a point light

- ask my client if he's cool with an all black version (j/k)

[INNEO_MWo]

Or maybe you can set the Ray bounce to 24?

[Eric Summers]

Could you post an image of your lighting settings? That might help determine the issue. I usually find that 1,000 samples gets me a pretty good result for clear plastic with white plastic behind.

[bdesign]

Have you tried rendering with Interior mode? It resolves caustics much faster and cleaner.

Cheers,
Eric

[RRIS]

I'll see what I can post tomorrow, but basically it's a transparent polycarbonate box with medical equipment inside (all transparent) and with lightpipes lighting something inside a metal container.
Using interior mode or product mode ended up not making much of a difference, except interior mode pretty much required caustics to be enabled for the object inside the container to be lit properly.
In the end that was a no-no, since it made other areas of the render unusable. Sadly, I have to say, because the light from the caustics was way more realistic than direct light only.

I'll probably end up re-rendering a region with interior mode  and caustics and photoshopping that in the rest.
Boosting the number of bounces helped with at least getting light through the whole setup.

I'm still left wondering what might cause these surfaces that receive photos from the caustics to have these darkened edges. Is it just that near the boundary edges of surfaces, photons can't bleed over and therefor it takes longer for those areas to brighten? I've attached a rudimentary copy of what's happening, with low samples. Even at 1300 samples (as I found out at work), those darkened edges are still there.

[INNEO_MWo]

Rendering with caustics needs a ground plane to catch them - by the way

[RRIS]

Rendering with caustics needs a ground plane to catch them - by the way

Any particular reason why? This box is an enclosed space, I did end up putting a physical plane underneath it all to catch reflections, but I don't see how a ground plane would be required?