2008

Physical Scale Sets a physical scale for exposure control to use with lights
that are not physically based. The result is an adjustment of the rendering
that approximates the eye's response to the scene.
Changing the value of Physical Scale is an optional step. Use it as a last resort
when the materials or maps are not rendering correctly. Changing this setting
will not affect anything in the scene unless your scene has an Ambient Color
different than black. If you do adjust it, set the Physical Scale value to the
equivalent of the brightest light source in the scene.
The software multiplies each standard light's
Multiplier on page 7859 by the
Physical Scale value to produce a light intensity value in candelas. For example,
with the default Physical Scale of 1500, a standard omni light is treated by
the renderer and radiosity as a photometric isotropic light of 1500 candelas.
Physical Scale is also factored into reflections, refractions, and self-illumination.
TIP When you use ray-tracing with self illumination, set Physical Scale to the
equivalent of the brightest light source in the scene. This sets the appropriate
conversion scale for reflections, self-illumination, and all other non-physically based
elements a material offers. In some cases, an object might reflect or emit more
light than the brightest light object in the scene; in this case, use the object's
Luminance value as the Physical Scale.
Range=0.0 to 200,000.0 candelas. Default=1500.0.
A single candle is approximately 1 candela (the unit can also be called a
"candle"). A 100-Watt (W) incandescent light bulb is approximately 139
candelas (cd). A 60W bulb emitting in all directions is about 70 cd, while the
same bulb with a reflector is about 4500 cd because the light flux is
concentrated into a narrow angle.
Photometric lights are unaffected by the Physical Scale value.
This parameter is animatable.
Exposure Controls | 6557