Watch Purkyně's Dusk (2021) : Full Movie Online Free Purkyně’s Dusk is an experimental short film based on the studies of light and colour carried out by the Czech physiologist Jan Evangelista Purkyně. The visual effect he described in 1825 determines that our perception of colour is dependant on the degree of illumination. Both the identifiable tints and the contrast between colours are perceived differently in bright or low light conditions.