I am currently trying to test polymer organic pigment's lightfastness and need to set up an exposure time to a light source.

Is there a difference in the rate of photodecomposition of pigment, or how the pigment decomposes between continuous exposure (e.g. sample continuosly exposed to light source for 48 hours) or intermittent exposure (e.g. 5 min exposure, 5 min darkness repeated until total exposure of 48 hours)?