Lighting - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 216

world Settings and Ambient Light
and occlusion
In Chapter 10, we baked ambient occlusion maps
for our projects. Ambient occlusion maps are tex-
tures that mimic the effect of light coming from
all around an object that is occluded, or blocked,
by parts of the object itself. This effect is similar to
what we see in the sky on a sunny day. The main
source of light is the sun, but light also scatters
throughout the atmosphere so that it comes from
all directions and even illuminates the shadows.
(This effect is even more apparent on an overcast
day when the lack of direct sunlight means things
are lit more evenly from all directions.)
To achieve the effect of light coming from a
scene's surroundings, we can use Blender's World
settings, accessible from the World tab of the
Properties editor. These settings determine the
look of your scene's background and how the back-
ground contributes to the scene's lighting. Both
Blender Internal and Cycles support world lighting,
though in slightly different ways.

World Settings in Blender Internal
Blender Internal's World settings are shown in
Figure 13-6. The most important ones are as
follows:

Horizon Color/Zenith Color/Ambient Color
By default, the sky in a scene will simply be the
Horizon Color . The Zenith Color is used when
Blend Sky is turned on, rendering the back-
ground as a gradient from the horizon color
to the zenith color. The Ambient Color is a fixed
color that is added to the lighting of every sur-
face in the scene, brightening the shadows, but
the effect is very unrealistic, so it's best to leave
this set to black.

Figure 13-6: Blender Internal's World settings

Ambient Occlusion We encountered ambient
occlusion in Chapter 10. Ambient occlusion
lights or adds shadows to a surface based on the
surrounding geometry. Areas with geometry
around them that blocks light will be darkened,
while the exposed parts of a mesh will remain
well lit. The Ambient Occlusion option can be
set to Add or Multiply with the other lighting
in the scene. Additive ambient occlusion bright-
ens the existing lighting, while Multiply adds
shadows. Multiply is the more “realistic” option
and is more suitable to most scenes. (The envi-
ronment lighting settings offer better tools for
adding further light to the scene anyway.)

Paper Sky/Real Sky Paper Sky applies any texture
or blend applied to the background to the cam-
era coordinates. This can be useful when you
have a background photo or image that you
want to use as is, without distortion. Real Sky
creates a background with a real horizon in
the plane of the scene's global coordinates so
that any textures remain static as the camera is
rotated and any blend in the sky occurs from
the “real” horizon upward (and downward).
Real Sky is useful when panoramic or mirror-
ball textures are used as backgrounds.