Jamieson, Fausset and Brown on Ephesians 5:11

11. unfruitful works of darkness--Sins are terminated in themselves, and therefore are called "works," not "fruits" (Ga 5:19, 22). Their only fruit is that which is not in a true sense fruit (De 32:32), namely, "death" (Ro 6:21; Ga 6:8). Plants cannot bear "fruit" in the absence of light. Sin is "darkness," and its parent is the prince of darkness (Ep 6:12). Graces, on the other hand, as flourishing in "the light," are reproductive, and abound in fruits; which, as harmoniously combining in one whole, are termed (in the singular) "the FRUIT of the Spirit" (Ep 5:9).

rather, &c.--Translate as Greek, "rather even reprove them" (compare Mt 5:14-16). Not only "have no fellowship, but even reprove them," namely, in words, and in your deeds, which, shining with "the light," virtually reprove all that is contrary to light (Ep 5:13; Joh 3:19-21). "Have no fellowship," does not imply that we can avoid all intercourse (1Co 5:10), but "avoid such fellowship as will defile yourselves"; just as light, though it touch filth, is not soiled by it; nay, as light detects it, so, "even reprove sin."