Light installations have been placed at locations around the city including Piccadilly, Mayfair, King's Cross, Trafalgar Square and Westminster.
Lumiere London runs from 18:30 GMT to 22:30 on Saturday and Sunday.
The art installations include a life-size 3D elephant, human figures floating in the sky, giant fish, LED stickmen and stars.
The festival has been developed by creative producers Artichoke.
London has been illuminated by its first festival of light, featuring 30 artists.