Ambient Occlusion role in Rendering

This example demonstrates the effect of the global ambient occlusion options.
The first image to the right is rendered with the Light cache for both primary and secondary bounces, Fixed Filter type for the light cache, and Store direct light off. The second image in the center is rendered with the same light cache settings, but with global ambient occlusion enabled. The third image to the right is rendered without ambient occlusion, with Brute force GI engine for primary bounces, and the Light cache as a secondary engine with Nearest Filter type. The render times include the time for calculating the light cache. Note how ambient occlusion can produce a feeling of a more detailed image, even though the result is not entirely correct.

Ambient occlusion is off – lighting is good, but there is a lack of detail Ambient occlusion is on – details are much more defined Brute force GI, no ambient occlusion – details are fine, but render times is longer.
For this image, the Caustics subdivs parameter for the light is set to 50, so that the separate photons are more distinct; the global caustics Multiplier is 17000, and the Max photons is set to 60. As can be seen, the larger search distance produces blurrier caustics.
Search dist = 1 Search dist = 10
Example 2: The light Caustics subdivs parameter
This example is similar to the previous one, but the Caustics subdivs parameter for the light is increased to 300. The other parameters are the same as in the previous example. As can be seen, the larger number of photons produces smoother caustics effects than in the previous example.