Its too bad light seems to be a problem

daveso

Rendering in DS with dark shadows and stuff just doesn;t seem to work all that well ..iray... 
it stays pretty much full of little white dots ... I suppose if I left it run for 6 hours or something it would clear out finally? or not
I'm defaulted at 2 hours right now, and that is about all can wait most of the time. sometimes I just post in the missing pixels. 

DrNewcenstein

I've let it run for 12+ hours with low light, and the fireflies sometimes do and sometimes don't vanish. However, I do get grainy shadows.

There are settings you can tweak in the Tone Mapping, but these increase the brightness of the image, which is not what I'm going for. If I wanted it brighter, I'd crank the lights. I want it dark, like it's actually being lit by the scant lighting in the scene. This is done in photography by setting a long exposure time, but tweaking this in D|S makes the whole scene brighter. I've tried cranking the Iterations to 15000 and the time to infinite (0), and nothing works.

Fishtales

If you have the Firefly Filter ON then try setting the Nominal Luminance to 1500 and see if that helps. Also try turning the Glossy Reflectivity down, don't go to 0.00 as I found that that increases render time, keep it above zero.

3Diva

You can render it brighter and with a few of the canvases, that way it renders faster - you can then adjust the brightness and shadow intensity and all that in post with the canvases. 

joseft

Grainyness in dark areas is caused by not enough light samples in the dark area, which makes it take longer to clean up

One thing you can try is to lower the exposure settings in DS (or in post) and increase the amount of light in the scene.

So obviously increasing the amount of light in the scene is going to make it brighter, which may not be the look that you want, but more light in the darker areas will make it clean up faster. So to counteract the extra light you are pumping into the scene, you lower the exposure settings to make the scene darker. Should help with cleaning up the darker areas.