Iray Lighting Problem

mikethe3dguy

I've been working on creating an interior fitness center space, and adjusting its appearance using feedback from the Nvidia Iray real time setting in viewport. I've got it just about where I want it, but once I started doing test renders I saw that the lights really aren't working at all. The lighting is provided by multiple hanging ceiling lights that I've attached the Uber emissive shader preset to..Virtually all surfaces are Iray shaders. While it looks fine in the viewport, in renders all I can really see are the surfaces of the lights themselves and some hotspot reflections of those lights on a few surfaces. Where am I going wrong? Have I misunderstood the use of the emissive shader?

Thanks!

 

maclean

You need to adjust the Exposure Value in Render Setting> Tone Mapping for an interior. It's default is 13.0, which is for a bright cloudy day. Drop it down to 7 - 8 for interiors. There's an EV guide here.

https://en.wikipedia.org/wiki/Exposure_value#Tabulated_exposure_values

fastbike1

Attaching the emissive shader preset by itself isn't enough.. Have you set the light temperature and levels as well?

mikethe3dguy

Color temps are set to 5000 in the portion of the scene in the render above, with levels at 7,000 KCd/m2 on each, which is likely too high for now.

Thanks for the advice on Tone Mapping: you're right, I did have it set to 13. Unfortunately changing it to 7 doesn't change the blackness of the render. Still looks the same, though I'll adjust my light levels down now for the new Tone Map settings so the scene doesn't look washed out in the viewport.

mikethe3dguy

O-kayyy... just discovered that my light level setting is NOT affecting the perceptible brightness of the scene, AT ALL. Even with light levels at ZERO the scene looks the same in viewport. I have environment mode set to Scene Only, and all headlamps are turned off, PLUS I have a headlamp blocker in the scene. Where could this light be coming from?

mikethe3dguy

Oh very strange: tried again and luminance setting is affecting viewport as expected. Early morning grogginess I guess: I probably was somehow not selecting ALL lights in the surface tab. Regardless, the renders are still black except for the light surfaces themselves.

With the new tone mapping setting of 7, proper light levels (at least in the viewport) appear to be about 100 KCd/m2.

mikethe3dguy

Oh! When I switch Render Mode to Photoreal it looks good! I had it set to Interactive. Any ideas why Interactive gives me stygian blackness?

Richard Haseltine

mikethe3dguy said:

Oh! When I switch Render Mode to Photoreal it looks good! I had it set to Interactive. Any ideas why Interactive gives me stygian blackness?

Interactive does not support all features that photoreal does - one of the differences is emissive surfaces.

mikethe3dguy

Well that is good to know! Thank you Richard.