Whatever is wholly deprived of light is in complete darkness.
Why not 'wholly deprived of light is complete darkness' ?
How can you conclude that "Whatever is wholly deprived of light" is darkness ? It clearly means that when a thing is deprived of light, it will remain in darkness. Something cannot be darkness. It can be placed in darkness. Darkness is not an object. Darkness is just the state of absence of light.
No, it would not be "complete darkness", because darkness is a noun that can mean
- the state of being dark, without any light
- Her face was in darkness.
It would be in this state, not be this state. For example, if you are talking about a bedroom, the bedroom would still be a bedroom. It would not cease to be a part of a building. There are two relevant uses of the word in:
- used to describe physical surroundings
- He was sitting alone in the darkness.
- used to show a state or condition
Note that darkness as used in that example, and your example, can mean something closer to "the places that are dark" than "the state of being dark".
What you could say is that
Whatever is wholly deprived of light is completely dark.
because dark is an adjective.