Plan that came to you when lit up? (6,4)

'up?' is the definition.
I know nothing about this answer so I can't tell whether this works.

'plan that came to you when lit' is the wordplay.
I cannot quite see how this works, but
'plan' could be 'idea' (both can mean an intention) and 'idea' is found within the answer.
'lit' could be 'bright' (similar in meaning) and 'bright' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?