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.

Bethan Rhys Roberts hosts Ask the Leader on BBC One Wales at 19:00 BST on Friday.
Carwyn Jones is a former barrister and Bridgend councillor who was elected to the assembly in 1999 and has been a Cabinet minister since 2000.
He is front and centre of an almost presidential election campaign by Welsh Labour, focusing on his six-and-a-half-year record in charge as first minister.
Opinion polls suggest the public rate Mr Jones more highly than his rivals, although the Conservatives are trying to drag him down by association with Labour's left-wing UK leader Jeremy Corbyn.
Former First Minister Rhodri Morgan paid tribute to Carwyn Jones as "the ideal person to have during a crisis", citing his handling of the 2001 foot-and-mouth outbreak while he was agriculture minister.
Labour sees the present steel crisis as giving Mr Jones an opportunity to portray himself as a national leader, standing up to the forces of global capitalism and a Tory government at Westminster.
But the opposition script says that if voters are not happy with the state of public services in Wales, they should blame the party which has been running the country for nearly 20 years.
Monday 11 April - Welsh Conservative leader Andrew RT Davies in Swansea
Tuesday 12 April - UKIP Wales leader Nathan Gill in Swansea
Wednesday 13 April - Welsh Lib Dem leader Kirsty Williams in Aberystwyth
Thursday 14 April - Plaid Cymru leader Leanne Wood in Aberystwyth
Ask the Leader can be seen on BBC One Wales at 19:00 BST on Friday and on the BBC iPlayer.
You can also follow the programme via social media - @walespolitics
London has been illuminated by its first festival of light, featuring 30 artists.
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Welsh Labour leader Carwyn Jones faces questions from an audience in Llangollen in the last in a daily series of live TV election specials.