An object (10) that during use is at least partly submerged in water, the object (10) comprising:- an anti-biofouling system (200) comprising an UV emitting element (210), wherein the UV emitting element (210) comprises:- one or more light sources (220) and is configured to irradiate with UV radiation (221) during an irradiation stage one or more of (i) a part (111) of an external surface (11) of said object (10) and (ii) water adjacent to said part (111) of said external surface (11), wherein the UV emitting element is configured to provide at least 80%, of the power of the UV radiation in a direction within an angle of 0-90° from a perpendicular to the earth's surface and in a direction below the object, relative to the object during its use.
