Abstract: In one general implementation, a method for identifying fluids in a wellbore includes generating light in a visible spectrum from a light source in a production wellbore; generating light in an ultraviolet spectrum from the light source in the production wellbore; receiving a first fluid in the production wellbore from a subterranean zone; receiving a second fluid in the production wellbore from the subterranean zone; capturing at least one image of a combined flow of the first fluid and the second fluid in at least one of the visible spectrum and the ultraviolet spectrum with an optical receiver in the production wellbore; and distinguishing, at least in part through the image, the first fluid from the second fluid in either or both the visible and ultraviolet spectrums.