Interior room with windows is too dim

[ssjenforcer191191191]

I am trying to light a building interior that has lots of windows.  However, the sky light inside the building is much less than viewed outside or with the building turned off for render.

I know I have to light it with lights inside, but isn't there a way to have the sky light penetrate the glass better to give more natural light to start with?

The windows all have a basic glass shader applied, but the lighting is very dim with how many windows there are (basically all windows).

[lee_griggs]

If there is glass geometry, ensure that caustics in standard_surface.advanced is enabled.

Also, increase the diffuse_ray_depth to allow more bounces of light into the room.

Are you using ACES color management?

Using a good tone mapping LUT can make the render look brighter and more photographic. I recommend: Kim Amland - Photographic 01 Linear.CUBE

Also, are you using light portals to reduce noise through the windows?

Please have a read through the Arnold for Cinema 4D User Guide.

[ssjenforcer191191191]

I'll try.

Yes, I am using the default ACES settings.

I just left the sunlight light settings default to interior only lighting.

I didn't notice any difference changing it to interior and exterior. 

[lizGYM66]

Can you show us the scene?

Unlike Corona which is good out of the box, I've found you have to tweak Arnold more to get the same results.

Things I've learnt:

Dome light on it's own is horrible for lighting interiors - to noisy.

Glass (windows) also adds to interior noise

Quad lights and distant light is the way to go (depends on scene of course)

Use a Sky for a little interior fill but not as the main source of light.

You need around 4-6 diffuse bounce rays

Materials make a huge difference.

Lifting the shadows and mid-tones gamma via the Color Correct imager does wonders. The attached images show before and after Color Correct imager.

Scene below was lit with 2 Quads, one outside the window (not close to it) with a narrow spread to push the light into the room without blowing out the window frame etc. Another quad as a fill outside of camera right and then a distant light for the sun. I also used an Arnold Sky (not physical) very low for some extra fill along with a portal light to help reduce noise from it.

It's not perfect it proved I could get an interior shot out of Arnold 🙂

[ssjenforcer191191191]

I tried turning on caustics for the glass, (image 2), and then increasing ray depth for diffuse (image 3), and it definitely helps a lot.

Very noisy, but I will tweak to reduce that.

I will try alternate light sources as you suggested to reduce noise further.

These examples are before I have split the window geometry and added a thicken to give it proper thickness for refraction accuracy.

[ssjenforcer191191191]

I just realized what you really meant by light portal. 

I thought you meant the checkbox inside the arnold sky object, but you meant the arnold light_portal.  I didn't know that existed.  I will try.  I guess I need one for each wall of windows?

EDIT:
The light portals only helped like 2% for noise in the big room in my scene.  Nothing significant.  I have one for each major wall of windows pointing inward on the outside of the glass.

[lee_griggs]

Try the light_portal with a skydome_light. If that doesn't work, you might fare better using quad area_lights as suggested by ssjenforcer191191191.

Some general room lighting tips here.