2008

Lighting Analysis
After you generate a radiosity solution, you can use the
Lighting Analysis tool
on page 6028 to analyze the lighting levels in your scene. This dialog provides
data on material reflectance, transmittance, and luminance.
You can also interactively visualize the light levels in the scene by using the
Pseudo Color Exposure Control on page 6552 . Rendering to a rendered frame
window displays an additional rendered frame with a legend below the image.
The legend correlates lighting levels and color values.
If you need to generate a lighting report, you can use the
Lighting Data
Exporter utility
on page 6559 to export the luminance and illuminance data to
a 32-bit LogLUV
TIFF file on page 7164 or a pair of PIC files on page 7151 (one
each for luminance and illuminance).
NOTE To obtain the most accurate quantitative analysis of lighting levels, you
should avoid using colored materials and diffuse maps.
Non-Physically Based Workflow
You don’t necessarily have to work with physically based lights and materials
in order to incorporate radiosity effects into your renderings. But there are a
number of issues that you need to consider:
■ Lights: Because the radiosity engine is physically based,
Standard lights
on page 4925 are interpreted by the engine as Photometric lights on page
4951 . For example, a Standard Spot light with a multiplier value of 1.0 will
be translated as a Physically Based Spot light with an intensity value of
1500 candelas (default value). This translation value corresponds to the
Physical Scale value in the various exposure controls.
In addition, if your Standard lights use custom attenuation settings (for
example, no attenuation, manual attenuation, or linear decay), the radiosity
engine will always solve for these lights using the physically correct Inverse
Square attenuation. This means that the amount of energy that bounces
between surfaces might not be equivalent to the way the Standard lights
render.
■ Natural Lighting: To simulate natural lighting without using the physically
based workflow described above, you can only use a
Direct Light on page
4932 for the Sun and
Skylight on page 4940 to produce skylight on page 7931
.
■ Exposure Control: Since Standard lights are not physically based, you
should only use exposure controls for the radiosity solution. Use the
5992 | Chapter 18 Rendering