Quick question: is the irradiance cache still needed in poser renders?  I'm asking particularly if you've got IDL on.  I remember it having something to do with AO but I don't know if it had other uses.  Is it doing anything for my renders at all?  Is it something I can ignore or do I need to turn it off?

Your best bet is to do a test render with a few different scenes with it on and off, at a high resolution and size so you can really SEE the difference and judge for yourself.  Test and experiment!

It was never "needed" unless you wanted a render this year, not next. That is still the case.

Okay, so it speeds up IDL too?

Yes - the irradiance cache avoids calculating the irradiance of the environment for every single pixel. Instead, calculations are performed on relatively widely spaced points and stored in the cache. Then every individual point is "lit" by interpolating the nearest cache values. The fewer calculated entries in the cache, the faster it is, but it's also less accurate.

Those red dots you see accumulating during IDL pre-calc are the cache entries.

Okay, thanks for letting me know. I didn't know if it was a legacy feature that was retained for backwards compatibility or not.