Abstract: A lighting unit for liquids comprises a tubular member with a flange at one end and a screwthread at the other whereby it can be secured in the wall of a vessel to hold liquid. A holder engaged in the rear end of the tubular member holds a bulb such as an automobile head lamp bulb, and a lens is mounted in a recess in the front end of the tubular member. The lens has a convex front face, a concave rear face and a negative focal length and, with the light mounted close to the rear of the lens, gives a very wide angle of illumination. The angle may for example be 172.degree. and the tubular member may be of only 7 cm diameter.