refraction is when light passes from one medium to another medium
flash is light. double_refraction is refraction. ultraviolet_lamp is source_of_illumination. ultraviolet_lamp is not source_of_illumination. red_light is not light_wave. contrast_medium is not medium. light is refracted_by_water. contrast_medium is medium. light is not refracted_by_water. floodlight is not light.