It says in the manual that even though ambient occlusion is just an approximation and faster than the option Full Indirect Lighting, it renders a more realistic light. I never really tried to figure out the concept of indirect lighting until now so just too what happended, I flicked on the ambient occlusion with the fedault settins and rendered my scene.

I couldn't really see any difference at all. I loaded various scenes and tried the same thing, still no visible difference in my renders. So I increased the ambient occlusion radius to 8 and tried again. Well, darker areas got even darker but not really something I've would have noticed if I didn't know to look for a difference. I cranked it up 25, yet again the darker areas got even darker and perhaps now there was a difference anyone could see. But darker areas? That's it? I could have made that postwork in two seconds in Photoshop.

So I was wondering, when does ambient occlusion take effect? Do I have to flick on sky lighting for it to be meaningful? Or put it this way, if I only have the basic default ambient light (set at 20%) and let's say two spotlights, will ambient occlusion make any sort of differences worth speaking of? Or is the ambient occlusion close connected to sky light and atmosphere?

Basically, how do I take advantage of ambient occlusion in Carrara? I just had big expectations when they started talking about realistic light and ambient occlusion in the manual. What should I think about when I set up lighting? Do I have to crank up the ambient light first?

 If you look at the things on the table around you that are not in direct sunlight or under a bright desk lamp, you'll notice that area closest to the objects are slight darker than further away. This is because the object prevents light from hitting the table from all directions. So, the light has been blocked. This blocking is also called occlusion. 

This effect is very dependent on scene scale. My coffee cup is blocking light and darkening the table top around it within about 2cm or 1/2 inch. So, if I was going to imitate that in Carrara, I'd need a "small" scale scene and an occlusion distance of  2 cm or .08 ft approx. 

Ambient occlusion in Carrara is done by telling the program to simply darken  any ambient light within x distance of the objects. If the number you choose doesn't reflect a realistic distance for the scale of your scene, it won't do anything for you.

Mark

Mark that was a good description for the AO... and I dont use AO in a real basis... when I want indirect light (radiosity) I just wait it to render that is a better effect then only AO... and the final result for AO is just this more deeo shadow in dark areas... just to create more volume in the scene.

Thank you for the input MarkBremmer! Excellent explanation with the table and objects around it. Now, this leads me to further questions.

1. How does the scene scale fit into the equation? The way I see it, a coffee cup would have the same occlusion in any kind of scene.

2. What if I have a scene with a coffe cup next to a tree? The cup would have 1/2 inch shadow while the tree have a longer, let's say 5 ft shadow. Just to wrap my head around it, what occlusion distance would you set?

3. Correct me if I'm wrong but the way you explain it, it sounds like the most realistic ambient occlusion would occur at infinite distance? This is just a hypothetical question since an infinite distance would take infinite time to calculate.

Quote - Mark that was a good description for the AO... and I dont use AO in a real basis... when I want indirect light (radiosity) I just wait it to render that is a better effect then only AO... and the final result for AO is just this more deeo shadow in dark areas... just to create more volume in the scene.

Are you talking about the setting "Full Indirect lighting"? Is that the same as radiosity? I'll take your word for it but what confuses me is that DAZ claim in the manual  that AO gives a more realistic light than full indirect lighting. Even though it's faster and just an approximation.

But you just confirmed my point, darker areas get darker when I use AO.

 Ambient Occlusion (AO) is a short-cut and not "real" environmental lighting. So, with your coffee cup v.s. tree example, you need to select a value that works well with a majority of the objects in your scene as compared to how your camera is placed. 

As a result, for long distance shots you'd set it for the tree; for close-ups, you'd set it for the cup.

As a rule, ambient occlusion is best used with architecture and geometrics.

Full indirect lighting is not radiosity but it does produce real AO. (Carrara doesn't actually do Radiosity - instead it does something called photon mapping which is faster) If you use a sky dome to illuminate your scene, there is no benefit to using AO. This is where you get into render settings and efficiencies. AO is good for stills and animations where there is lighting sources but possibly motion in an animation. AO will give you increased render speeds across your animation as compared to using Indirect Lighting. 

On the other hand, if you have a scene animation  where you want to light it with a sky dome but nothing in your scene moves but the camera, than saving and using an irradiance map is the way to go. 

I notice a difference if you have a background set. (Pick scene from the instances list and go from there.) Then it picks up light from the background color. If the background is left alone or set to a really dark color, then ambience doesn't pick up much at all. What it mostly seems to do is affect how shadows appear by picking up scattered light. Otherwise you just get really contrasty pics in regards to light and shadow.