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Lighting Design Glossary

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Umbra
Penumbra

(Terms of physics/lighting)

The shadow volume behind an object lit by an area light source (in contrast to a point light source) doesn't have sharp boundaries. This is caused by the fact that each point in the boundary area is only partially shadowed. The area (volume) in full shadow is the umbra, the boundary area the penumbra.

illustration of umbra/penumbra

(The graphic is actually inaccurate, since the penumbra doesn't have a constant shadow density, but rather a gradient ranging from shadow to light)

 

References:
   light
 
 
English    German
penumbra    Der Halbschatten
umbra    Der Kernschatten
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