Hi,
we’re having problems with vray taking 10+ mins to merge light cache passes.
this is on a simple scene with light cache on very low settings - 200 subdivs.
prefilter also takes 2 mins even though its unticked in the settings.
during this process, cpu utilization is at 1%.
basically, 90% of the render time is spent on merging the light cache 
were using build 1.00.74, and sketchup free (ran out of licenses for pro)
any help would be appreciated.
Re: Vray taking forever to merge light cache passes
I copy that… light cache passes taking 12-odd mins with a 750kb (1400 faces)skp file… 
Macho
Re: Vray taking forever to merge light cache passes
On a scene I was doing I tried QMC instead of Lightcache for secondary -just to test the visual difference- and the rendering time where cut from 15mins to 5mins. Something that surprised me as I’ve always thought that Lightcache was faster than QMC. That was with 1.00.74
Haven’t had a chance to test the same scene with the original release. The model had allot of geometry, 700.000-800.000 polygons, with an light grey override material.
Re: Vray taking forever to merge light cache passes
this is definitely a bug.
here is a workaround:
while vray is merging light cache passes or prefiltering, click and hold on the title bar of the info dialog, and it will suddenly shoot up to full speed and 100% cpu utilization.
merging goes from 10 mins to 10 seconds :
very strange indeed. seems to be some kind of focus bug.
Re: Vray taking forever to merge light cache passes
There’s no longer QMC; its been replaced by DMC, and yes, even I have noticed significant time gains while using DMC as 2nd R.E.
I was all the more surprised with this result more so because even the Manual mentions using L.C. as 2RE. Could Damien/ Joe/ anyone elaborate how LC provides a quicker render? Is it possible only in the 2nd (& thereafter) renders with the proviso that we use pre-saved vrlmaps for subsequent calculations? I even tried using the presaved map option, but the result comes out unsatisfactory almost every time. Maybe I’m missing something?
Could anyone explain the basic workflow to use while tweaking interior lighting of (totally) enclosed spaces. I can mention my way of approach on how I used it with mR+Max: -
1. Complete your Model with everything except high poly objects like plants, heavy poly furniture, detailed objects etc. (Use simple low poly components as dummy objects in their place; and replace them later at time of final render);
2. Set up your scene & VRay lights; for the time being switch all lights OFF;
3. In VRay Options window, make following settings: -
a. Uncheck both GI & Background boxes in Environment panel;
b. Uncheck Default & Hidden lights- this will make way to provide you with a totally black render for your completely enclosed space;
c. Check Override materials in the Global parameters panel- this is to provide you with a scene in ‘monochrome’ mode; so that we can then tweak all lights to our satisfaction;
d. Select IM & DMC as primary & secondary R.Engines respectively in the Indirect Lighting panel;
e.In IM panel, Set min/max rates to -4 & -3 respectively, don’t change any other setting in this panel;
f. In DMC panel, select adaptive DMC;
g. In output panel, set size to 480x360 (this gives a good enough test render window size; I use 27 inch lcd panels on which this size seems okay);
4. Render.
This will give you a totally black render. Now switch on your lights one by one while tweaking their setting to your satisfaction until you reach on position of all lights on with good lighting levels.
Now is the time to assign your materials (even to your dummy objects) so as to get ‘some previews’ of what your final renders are gonna look like. Then, when you feel no more tweaking of lights & materials is necessary, replace your dummy objects with the real objects, change output size to what you want, change min-max rates in IM panel to -3, 0 (or if you’re experienced, to the levels you want); and hit Render… Hopefully, you will be very satisfied with your results.
Macho
Re: Vray taking forever to merge light cache passes
cadmonkey, I can confirm this bug. Just posted a ticket at the support section.
Cheers
eph
Re: Vray taking forever to merge light cache passes
thanks eph. nice to know it’s not just me.
i’ll post a ticket when IT finally get round to telling me my serial number 
Re: Vray taking forever to merge light cache passes
I have tips on this issue.
UNCHECK batch render,then go!
enjoy speed!
And more, you can operate on SU while rendering
Check post below for detail:
http://asgvis.com/smf//index.php?topic=4983.msg26636#msg26636