8

1192 Chapter 15: Lights and Cameras
Decay group
Decay is an additional way to make a light’s
int ensity reduce over distance.
Ty pe —Setsthetypeofdecaytouse. Thereare
three types to choose from.
•
None—(The default.) Applies no decay. The
light maintains full strength from its source to
infinity, unless you turn on far attenuation.
•
Inver se—Applies inverse decay . The formula is
luminance=R
0
/R, where R
0
is the radial source
of the light if no attenuation is used, or the Near
End value of the light if attenuation is used.
R
is the radial distance of the illuminated surface
from
R
0.
• Inver se S quare—Applies inverse-square decay.
Theformulaforthisis(R
0
/R)
2
.Thisisactually
the "real-world" decay of light, but you might
find it too dim in the world of computer
graphics.
This is the decay formula used by
photometric
lights (page 2–1155)
.
Tip: IfInverseSquaredecaymakesthescenetoo
dim, you can t ry using the
Environment Panel
(page 3–268)
to increase the Global Lighting
Level value.
The point at which decay begins depends on
whetherornotyouuseattenuation:
• With no attenuation, decay begins at the source
of the light.
• With near attenuation, the decay begins at the
Near End position.
Once the beginning point is established, the decay
follows its formula to infinity, or until the light
itself is cut off by the Far En d distance. In other
words,thedistancebetweenNearEndandFarEnd
doesnotscale,orotherwiseaffect,theapparent
ramp of decaying light.
Tip: Because decay continues to calculate dimmer
and dimmer values as the distance of the lig ht
throw increases, it’s a good idea to set at least the
Far End of attenuation to eliminate unnecessary
calculations.
Near Attenuation group
Start—Sets the distance at which the light b e gins
to fade in.
End—Sets the distance at which the light reaches
its full value.
Use—Enables near attenuation for the light.
Show—Displays the near attenuation range settings
in v iewports. For spotlights, attenuation ranges
appear as lens-shaped sections of the cone. For
directionallights,therangesappearascircular
sections of the cone. For omni lights and spot or
directional lights with Overshoot turned on, the
ranges appear as spheres. By default, Near Start is
dark blue and Near End is light blue.
Far Attenuation group
Start—Sets the distance at which the light b e gins
to fade out.
End—Sets the distance at which the light has faded
to zero.
Use—Enables far attenuation for the light.
Show—Displays the far attenuation range settings
in v iewports. For spotlights, attenuation ranges
appear as lens-shaped sections of the cone. For
directionallights,therangesappearascircular
sections of the cone. For omni lights and spot or
directional lights with Overshoot turned on, the
ranges appear as spheres. By default, Far Start is
lightbrownandFarEndisdarkbrown.