Make sure you don't leave the lights on when you leave the room.
Literal
Room [object-を] exit [when-とき] [topic-は] electric-light [object-を] left-on [make not-にしない] [so as not to-ように] [right?-ね].
Introduces ~っぱなし — つけっぱなし means 'left turned on,' carrying a nuance of carelessness. Combined with ~ないように (so as not to), the sentence is a gentle warning against a bad habit. The final ね softens it further.