My father always checks whether all the lights are off before going to bed.
Literal
Father [topic-は] always, sleep before lights [subject-が] all gone-out [whether or not-かどうか] confirms.
Two useful patterns interlock: ~前に ('before doing X') and ~かどうか ('whether or not X'). 明かりがみな消えている checks the resulting state (ている) of all lights being extinguished. 確かめる means 'to verify/confirm.'