The aim of this project is to use Arctic diatoms to study the effect of photoperiod and light spectrum on the rhythmicity of physiology and metabolism in order to propose new blue:red light regimens with positive effect on the biological clock, for potential applications for non-invasive medical light treatments (‘light therapy’). In parallel, the project will 1) deepen our knowledge of the fundamental regulatory processes behind the light-driven ecophysiology of diatoms, the sentinels of climate changes in the Arctic, 2) open on bioprospection of added-value molecules beneficial to human health, i.e. carotenoid pigments and polyunsaturated lipids found in Arctic diatoms.