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302 Chapter 18: Effects and Environments
Left: Linear scale
Right: Logarithmic scale
Display R ange group
Mini mum (M in. )—Sets the lowest value to measure
and represent in the rendering. Values at this
quantit y or b elow it all map to the leftmost display
color (or grayscale level).
Maximum (Max.)—Sets the highest value to
measure and represent in the 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 3–977) is
multipliedbythePhysicalScalevaluetogivea
light intensit y 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 lig ht of 1500 candelas.
Physical Scale is also factored into reflections,
refractions, and self-illumination.
Tip: You need to set the Physical Scale when you use
ray-tracing with self illumination. Set t his value
to the equivalent of the brightest 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 mig ht reflect or
emit more light than the brig htest 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.
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 al l
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 Physic al
Scale value.
This parameter is animatable.
Adjusting the range to analyze:
Above: Correct range for a scene
Middle: Too n arrow a range
Below:Toogreatarange
Narrowing t he range to focus on a single object
General Guidelines for Physical Scale Values
•IfyouuseonlyPhotometric lights (page 2–1301),
IES Sun (page 2–1309),andIES Sky (page