LC and LC

[glorybound]

Has anyone found lightcache working well for exterior scenes; both first and second bounces? I am trying to get my render times down, and LC+LC seems to be the ticket.

[flino2004]

reducing your rendertime is becoming an obsession for you..... Bobby, the quality of your work has been improved a lot in the last year and trading quality for rendertime (stills) is not a good idea in my opinion...maybe you have to think in other solution, you use a lot displacement for shingles, siding, trims, stone, etc....I usually use it for stone and sometimes brick if the camera is very close. Maybe the solution is normal maps and/or geometry.

[glorybound]

obsession.., me? . It's all just a chess game, isn't it?

I haven't been one to spend hours optimizing, just to save minutes, but I do want to get better. I spend a lot of time starting and stopping. If my scene is optimized better than I can stop and start more often, if that makes sense. I once tried to model my siding, but it didn't work out as well. I have always wondered why their wasn't a siding script floating around. Anyway, some of these small things that are never asked sometimes can save a ton of time. Like, I didn't know that using a VRayExtaTex can double your rendering time.

[glorybound]

Hmmm... here, he used a script for the siding.

http://www.ronenbekerman.com/making-of-narrabeen-house/

[Neilg]

If you're looking to speed up renders, do the IR/LC pass with glossy effects and reflections turned off. Use the VMC script to turn reflections off - you still need refraction.

This will be miles faster. you may be able to switch off displacement for it too.

[glorybound]

I will try it. Isn't glossy effects per material? So, as you build your shader, you have to click the radio button off. Now, don't you need reflections on? I mean, glass reflects.

If you're looking to speed up renders, do the IR/LC pass with glossy effects and reflections turned off. Use the VMC script to turn reflections off - you still need refraction.

This will be miles faster. you may be able to switch off displacement for it too.

[Neilg]

There's a global glossy effects switch in the main settings.

Forgot about glass - I render it as a separate pass, so in my scenes it doesn't reflect. Sometimes that doesnt matter though - most of what you see in reflections is a silhouette, it's rare that glass actually reflects something that needs definition.

[svetlozar.draganov]

There are hundred of ways to optimize your scene for rendering with Vray, one of those could be to use only Light Cache for Global Illumination.
From technical stand point there is no need for adding both GI engines to use LC - because it doesn't matter whether you have one or two LC algorithms , Vray will calculate only one LC Illumination and the end result will be always the same with one or two LC engines.

In general LC handles secondary bounces and since all bounces except the first one doesn't require very precise result it is developed to work faster instead of very accurate.
Follows from the above it seams that we could speed up a lot GI-calculations at the cost of low-quality GI-solution, it is up to you to decide whether this quality is sufficient or not.
You have to have in mind that LC may produce blotchiness, light-leak artifacts, too-smoothed GI and not very well defined details - although sometimes the result might look just fine.

Materials optimizations could also speed up a lot render-time. For example you could use a simplified GI / Reflection / Refraction materials through VrayOverrideMtl.
For still-images using Reflect and Refract Interpolations will speed-up a lot calculations of these properties.

Another workaround is to Fake GI with the help of VrayAmbientLight with assigned VrayDirt texture - and you don't need to calculate any GI in the scene.

In general the most amazing feature of Vray is that you can optimize you scene unlimitedly but the equation is always the same:
Faster Render Times equals Lower Image Quality - and the user must determine in which way to tip the scales.