Abstract: A lamp capable of underwater use comprises a rectangular acrylic body with elongate V-shaped recesses in a major surface each receiving an elongate Beta-light. An acrylic cover plate is sealed to the major surface and the body is secured to a steel backing plate with a neoprene layer between to help dissipate shock loadings. The sides of the recesses include an angle of 78.degree. to enhance reflection and may be formed by a reflective lining. The Beta-lights can be received in the grooves by shock absorbent O-rings grouped in pairs with adhesive in between. In a modification a disc-shaped Beta-light is encapsulated and received in a body formed by pour molding which is closed by a cap which is ultrasonically welded into place.