A lighting unit for water fountains, ponds and the like, has a housing that is sealed at least relative to splashing water. A light source is arranged in the housing. A lens is arranged in the housing for alignment of light emitted by the light source. An additional lens unit is arranged in a light path of the light emitted by the light source for providing an additional alignment of the light emitted by the light source. A closure cap secures the additional lens unit by a self-centering action on the housing. The closure cap has an inner guide providing the self-centering action.