The device (1) has a glass optics (5) and a support (2) defining a hollow chamber (9), and LEDs (8) arranged on a front face of a heat conducting plate (13). The plate is arranged on the optics so that the LEDs are located in the hollow chamber and all or part of a rear face of the plate is located outside the chamber to be in contact with water in a pool. The LEDs are arranged on the plate so as to emit a light flux (F) in a direction opposite to that of the optics. A reflector (18) is arranged in the hollow chamber to redistribute the light flux in the direction of the optics.
