"Put out the light, and then put out the light" (V.2.7) of Shakespeare's Othello is said as a soliloquy by Othello right before the scene in which he finally takes action and murders Desdemona.
At the beginning of this soliloquy, Othello is comparing Desdemona's life to the flame on a candle. He realizes he can snuff out her life just as he does the flame of a candle. However, he realizes that if he takes this step, he can never get Desdemona back unlike with a candle which he always just relight.
Although Othello seemed resolute in the previous scene, he is again wavering about his decision in these lines. Once she is awakened, all his doubts about killing her seem to disappear immediately. It is as if he sees Desdemona at her most pure and innocent when she is lying unconscious there and wants to preserve that purity by prohibiting her from being conscious anymore.