The artist Sutapa Biswas’s father was a legendary figure in her relatives: a Marxist agronomist who stood up to the governing administration in west Bengal around environmental abuses, and smoked joints in a moonlit Taj Mahal (he broke in). Still it is her mother’s knowledge that anchors the artist’s new docufiction film Lumen, about a lady who travelled alone with five youngsters, next her husband to England to make a new lifetime. “She struggled,” Biswas claims. “1960s Britain was racist. She truly craved climbing trees or swimming in her sari.” Lumen slips between bittersweet feeling reminiscences of her dropped residence – its exceptional greens, the scent of frangipani – and…