Umbrosity

the interstitial divisions being continuated by the accession of oil, it becometh more transparent, and admits the visible rays with less umbrosity

Shrubberies.[…]The judicious introduction of views of more distant scenery; which is most frequently desirable, unless in such parts as, by way of contrast, are preserved in umbrosity.

Cotton is grown here as an annual, yet in some strong lands it is allowed to remain in the ground for two seasons[…]from the umbrosity of its foliage, and its hoeings, it leaves the land, in a fit and open state to receive a winter crop.

The architecture of winecellar-cum-dungeon prohibited a smooth transition from illumination to umbrosity. Lasse's logic was sound: Concentrate on the penumbral areas; any useful item in the deep shadow cannot be seen and any such object in the light will have been removed.