Lighting - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 217

Environment Lighting This adds light to a scene,
coming from all directions (though blocked by
nearby geometry, as with ambient occlusion).
The Environment Lighting setting can be used
to mimic scattered light from the sky in an out-
door scene or to approximate the effect of light
bouncing around and illuminating a scene. The
color of the environment lighting can be set to
white, to the sky color (where it will use the hori-
zon color or both the horizon and zenith colors
if you have a blend sky), or the sky texture if you
are using a background texture.

with lamps, R ay Trace takes multiple ray-traced
samples per pixel to determine the amount of
world lighting. This process gives more accu-
rate results, typically at the cost of extra render
time and noise (if the number of samples is
set too low). The Approximate setting does not
require ray tracing and is noise free, but it can
produce other artifacts, such as overocclusion
in some areas. Turning up the number of passes
and setting the error value lower gives better
results but takes more time to preprocess when
rendering. Alternatively, using the Correction
parameter reduces the strength of the occlusion
to compensate for the artifacts. When using the
Approximate Gather method, turning on Pixel
Cache generally gives much faster results.

Indirect Lighting This setting allows Blender
Internal to simulate the effect of light bounc-
ing repeatedly, and thus illuminating more of a
scene, before entering the camera or eye. The
result can be color bleeding, where the color of
a brightly colored diffuse material is reflected
onto nearby objects (as shown in Figure 13-7).
The method is only compatible with the Approx-
imate Gather method (discussed below). The
Factor setting affects the strength of this effect,
and the Bounces setting determines how many
times light may bounce off a surface and still be
rendered.

Attenuation The Falloff setting under Attenua-
tion causes ambient occlusion, environment
lighting, and indirect lighting to fade out over a
certain distance, reducing the effect of far away
geometry on a surface and lightening the sur-
face. Falloff also speeds up rendering because
calculating the lighting for a surface point only
requires taking nearby geometry into account.
The Strength setting determines how strong the
attenuation is, while the Distance setting (only
with the Ray-Trace Gather method) determines
the range of the falloff.

Gather (Ray Trace and Approximate) These set-
tings let you choose between Blender Internal's
two options for rendering world lighting. As

Figure 13-7: Color bleeding from indirect lighting. Here, the red sphere reflects red light onto its surroundings. This is
most visible on the gray inner sphere. This is a subtle effect, so indirect light alone is shown on the right. The surround-
ings also contribute indirect light, shown as grayish colors in the image on the right.