Hmm.. this looks really bad. The shadows are unrealistic and sharp and there is no ambient light. I could turn up the ambience of the textures but that would only make the render look milky.

Let's try softening the shadows by turning on the "soft shadows" option for the sun. The scene now took about 10 times longer to render and the shadows got blurred. The scene still looks very bad.

Now I turned off the soft shadows for the sun and turned on "True Ambience" (I had to switch to Premium AA to be able to turn on this option).

Compare with Image 1. This one looks slightly better but still not realistic.

Here is a screen shot showing the scene (from above). The red spheres are radial lights placed in a semi dome around the scene.

Ah yes! This is starting to look nice! A dome with 115 lights is used and the sun is disabled. The shadows on the object are nice and smooth and you can now see all the details that where hidden before. However, render time increased dramatically and the shadows on the ground are jagged and aren't good enough.

I added a second light dome with 85 additional lights (now 200 in total) and you can see that this also smoothed the shadows on the ground.

Since the shadows on the object looked ok already with 115 lights then lets try decreasing to 50. In this image 50 lights are used and the shadows on the object look nice (but not on the ground) and the render time is much shorter. I had to increase the lights intensity (from 1 to 3) to compensate the fact that less light sources are used. I missed to adjust the diffusion level on the textures and they now look over-exposed in some places.

Conclusion: 50 light source can be enough depending on your scene (but 50 are not enough in this scene because the shadows on the ground look jagged).

How about enabling "soft shadows" for the 50 light sources? As you can see that didn't help much (compare with 6). Render time jumped from 3 min to over 2 hours and the result isn't that much better. The shadows on the floor are still jagged.

Conclusion comparing with image 5: Using more lights instead of "soft shadows" generates a much better result and in a shorter time.

Different AA quality levels don't affect the light but a comparison may be interesting. Compare this Super AA render to image 4, it looks cleaner but took 5 times longer to render. This image is a bad example actually - higher AA-levels are meaningful in scenes where there are lots if detailed and cluttered objects in the background. I've also noticed that high-contrast edges between foreground and background objects look much better with higher AA-levels but that's a different story.

Highest possible AA-level. Slightly better edges but hardly worth the wait (in this case). On a printed version the difference is easier to spot.

You can of course combine light domes with the "sun". In this one the "sun" killed off the jagged shadows on the ground and added an outdoor feeling to the scene. Using more than 50 lights in a scene like this would just be a waste of time. Better spend it on improving the texture settings (which I didn't).

This one uses the exact same settings as image 4 but the size of light dome has been increased about 10 times. The shadows on the floor are still jagged, slightly less perhaps.

In this on I tested enlarging the size of the light spheres. No difference what so ever (compare with image 10) except a longer render time (?!) Or?