The illuminations float over the crowds in Piccadilly
Transport for London (TfL) have warned that roads will be closed and Tube stations will be busier than usual in the areas where the festival is being held.
A number of buses will be diverted or terminate early.
It has been created by producers Artichoke, who held a similar event in Durham.
As well as a "huge" production crew, the company has recruited volunteers from Team London, which supported the London Olympics, to help guide people around the installations.
"The arts should be free and available to everyone," Artichoke's director Helen Marriage told BBC London.
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