Penumbra

n.	1.	An incomplete or partial shadow.
	2.	(Astron.) The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light.
	3.	(Paint.) The part of a picture where the shade imperceptibly blends with the light.

Noun

1.

penumbra - a fringe region of partial shadow around an umbra

shadow