8

298 Chapter 18: Effects and Environments
Left: Linear scale
Right: Logarithmic scale
Display Range group
Mini mum (Min. )—Sets the lowest value to measure
and represent in the rendering. Values at this
quantit y or below it all map to the lef tmost display
color (or grayscale level).
Maximum (Max.)—Sets the highest value to
measure and represent in t he rendering. Values at
this quantity or above it all map to the rightmost
display color (or gr ayscale value).
Physical Scale—Sets a physical scale for exposure
control to use. The result is an adjustment of the
rendering that approximates the eye’s response to
the scene.
Each standard light’s
Multiplier (page 3–1071)
is m ultiplied by the Physical Scale value to give
a light intensity value in candelas. For example,
w ith 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: You need to set the Physical Scale w hen you use
ray-tracing with self illumination. Set this value
to the equivalent of the br ightest light source in
thescene.Thiswillsettheappropriateconversion
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 li ght 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.
Asinglecandleisapproximately1candela(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.
Adjusting the range to analyze:
Above: Correct range for a scene
Midd le: Too narrow a range
Below: Too great a range
Narrowing the range to focus on a single object
General Guidelines for Physical Scale Values
•Ifyouuseonly
Photometric lights (page
2–1155)
, IES Sun (page 2–1163) ,and IES Sky