Othello has a monologue in the opening of scene ii explain what, " Put out the light of the candle, and then put out the light of her heart./ If I extinguish the candle, I can light it again if I regret it./ But once I kill you, you beautiful, fake woman

Othello is contemplating killing Desdemona using candlelight as a metaphor. He can always light a candle again if he kills its light, but he cannot give Desdemona's light (of life) back if he kills her. Othello is bent on killing Desdemona because he believes she has deceived him hence "fake woman".