Photoinhibition of photosynthesis in the red alga Chondrus crispus from different shore levels was investigated under laboratory and field conditions. The underwater light climate at Roscoff (French Atlantic coast), characterized by transmittance spectra, was shown to be intermediate between Jerlov coastal type 1 and oceanic type III. Chondrus crispus thalli were collected at four depths (3·5–8·5 m below high tide level) and exposed to daily courses of artificial and natural light. Filters were used to discriminate between the effects of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) under the photoinhibitory treatments. In the presence of natural UVR, photoinhibition at midday was increased by up to 60%. Recovery from photoinhibition was measured at different times throughout the light stress. Recovery kinetics differed between morning and early afternoon in all treatments, and were dependent on the light dose. Whereas biphasic kinetics were observed in all treatments in the morning, the recovery in early afternoon was significantly slower. The influence of UVR on recovery was apparent after exposure to higher light doses. In all investigations, sensitivity to photoinhibition corresponded to zonation of the algae, with deeper-growing algae showing a greater depression of fluorescence yield, and slower recovery (indicating acclimation to the growth irradiance). An increase in the phycoerythrin content and increasing photosynthetic efficiency with increasing growth depth were observed.