Given the question: Information:  - Leonard Charles Huia "Len" Lye (5 July 1901  15 May 1980), was a Christchurch, New Zealand-born artist known primarily for his experimental films and kinetic sculpture. His films are held in archives including the New Zealand Film Archive, British Film Institute, Museum of Modern Art in New York City, and the Pacific Film Archive at University of California, Berkeley. Lye's sculptures are found in the collections of the Whitney Museum of American Art, the Art Institute of Chicago, the Albright-Knox Art Gallery and the Berkeley Art Museum. Although he became a naturalized citizen of the United States in 1950, much of his work went to New Zealand after his death, where it is housed at the Govett-Brewster Art Gallery in New Plymouth.  - The British Film Institute (BFI) is a film and charitable organisation which promotes and preserves filmmaking and television in the United Kingdom.  - John Grierson (26 April 1898  19 February 1972) was a pioneering Scottish documentary maker, often considered the father of British and Canadian documentary film. In 1926, Grierson coined the term "documentary" in a review of Robert Flaherty's "Moana".  - Rainbow Dance is a 1936 British animated film , created by New Zealand - born animation pioneer Len Lye and released by the GPO Film Unit . This is Lye 's second film to be viewed by the public . It uses the Gasparcolor process . Credits also list Australian music pioneer Jack Ellitt ( `` Synchronization '' ) and Frank Jones ( `` Camera '' ) .  - The GPO Film Unit was a subdivision of the UK General Post Office. The unit was established in 1933, taking on responsibilities of the Empire Marketing Board Film Unit. Headed by John Grierson, it was set up to produce sponsored documentary films mainly related to the activities of the GPO.    Given the information above, choose from the list below the object entity that exhibits the relation 'producer' with the subject 'rainbow dance'.  Choices: - british film institute  - john grierson
The answer is:
john grierson