English usage – conditional transformation: Improve the mixed conditional by choosing the best form to express a past unreal condition about room brightness and the resulting ability to read.

Given sentence
'If the room had been brighter, I would have been able to read for a while before bed time.'

Concept/Approach
The sentence is a correct third conditional (past counterfactual). A concise, formal improvement is to use the standard inversion that omits 'if': 'Had + subject + past participle, …'

Improved version
Had the room been brighter, I would have been able to read for a while before bedtime.

Common pitfalls
'If the room was' mixes condition types; 'If the room are' is ungrammatical.

Final Answer
Had the room been brighter