Creating Soft Shadows with Area Lights
Area lights are a special kind of point light and spotlight. The rays emanate from a geometric area instead of a single point. This is useful for creating soft shadows with both an umbra (the full shadow where an object blocks all rays from the light) and a penumbra (the partial shadow where an object blocks some of the rays).
The chess piece on the left is lit by a standard point source light producing sharp shadow edges. The same piece on the right is illuminated by an area light which creates blurred shadows.
The shadow’s relative softness (the relation between the umbra and penumbra) is affected by the shape and size of the light’s geometry. You can choose from a variety of geometry and transform the geometry area as you wish.
To determine the amount of illumination on a surface, a sample of points is distributed evenly over the area light geometry. Rays are cast from each sample point; all, some, or none of the rays may be blocked by an object. This creates a smoothly graded penumbra.
For complete information about working with area lights, seeand [ ].
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