Like a formal dress on a drunken hen grappling with uneven light (4-6)

'uneven light' is the definition.
Both the definition and answer are adjectives. Maybe there's a link between them I don't understand?

'like a formal dress on a drunken hen grappling' is the wordplay.
I cannot quite see how this works, but
'dress' could be 'full' (full dress is a kind of dress) and 'full' is present in the answer.
The remaining letters 'length' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

'with' is the link.

Can you help me to learn more?