Vertical profiles of underwater photosynthetic active radiation (PAR) are collected on a monthly basis in the Gulf of Trieste – time series station (station C1). The site is part of the LTER-North Adriatic site.Data are used to characterize the light field and light extinction in the coastal Long Term Ecosystem Research station of the Gulf of Trieste, in the northernmost part of the Adriatic Sea and of the Mediterranean basin. General information can be found at: http://nettuno.ogs.trieste.it/ilter/BIO/index.html