Jamieson, Fausset and Brown on Ephesians 5:13

13. that are reproved--rather, "when they are reproved," namely, by you (Ep 5:11).

whatsoever doth make manifest--rather, "everything that is (that is, suffers itself to be) made manifest (or 'shone upon,' namely, by your 'reproving,' Ep 5:11) is (thenceforth no longer 'darkness,' Ep 5:8, but) light." The devil and the wicked will not suffer themselves to be made manifest by the light, but love darkness, though outwardly the light shines round them. Therefore, "light" has no transforming effect on them, so that they do not become light (Joh 3:19, 20). But, says the apostle, you being now light yourselves (Ep 5:8), by bringing to light through reproof those who are in darkness, will convert them to light. Your consistent lives and faithful reproofs will be your "armor of light" (Ro 13:12) in making an inroad on the kingdom of darkness.