A lamp (L) comprising: - a cylindrical structure intended to be fixed to a face of a wall (P) provided with a hole and on an inner side of the face of a wall (P), such that a proximal part and a distal part of the cylindrical structure are defined with respect to the face of the wall (P), the cylindrical structure being opened at the part proximal to the face of the wall (P); and - a light source ; which comprises a sliding piston mounted in the cylindrical structure , the piston comprising the light source such that the configuration of the lighting of the lamp (L) can be adjusted by moving the piston through the cylindrical structure characterized in that the cylindrical structure comprises on the inner surface thereof, or the piston on the side surface thereof, at least one guide with a closed route (G), such that an upwards path (GS) and a downwards path (GB) are defined, connected by the upper and lower ends thereof, the upwards path (GS) being provided with elastic tabs that protrude from the inner surface of the cylindrical structure , or, from the side surface of the piston, respectively, the piston or the cylindrical surface , respectively, being provided with at least one retaining projection , the retaining projection being arranged to slide on the guide (G), the elastic tabs being arranged to bend and not retain the piston when the same moves from the proximal part to the distal part, but to retain it when moving in the opposite direction, the upper end of the guide (G) being configured to take the retaining projection from the upper end of the upwards path (GS) to the upper end of the downwards path (GB) when the piston reaches a maximum height and the lower end of the guide (G) being configured to take the retaining projection from the lower end of the downwards path (GB) to the lower end of the upwards path (GS) when the piston reaches a minimum height. - a cylindrical structure intended to be fixed to a face of a wall (P) provided with a hole and on an inner side of the face of a wall (P), such that a proximal part and a distal part of the cylindrical structure are defined with respect to the face of the wall (P), the cylindrical structure being opened at the part proximal to the face of the wall (P); and - a light source ; which comprises a sliding piston mounted in the cylindrical structure , the piston comprising the light source such that the configuration of the lighting of the lamp (L) can be adjusted by moving the piston through the cylindrical structure characterized in that the cylindrical structure comprises on the inner surface thereof, or the piston on the side surface thereof, at least one guide with a closed route (G), such that an upwards path (GS) and a downwards path (GB) are defined, connected by the upper and lower ends thereof, the upwards path (GS) being provided with elastic tabs that protrude from the inner surface of the cylindrical structure , or, from the side surface of the piston, respectively, the piston or the cylindrical surface , respectively, being provided with at least one retaining projection , the retaining projection being arranged to slide on the guide (G), the elastic tabs being arranged to bend and not retain the piston when the same moves from the proximal part to the distal part, but to retain it when moving in the opposite direction, the upper end of the guide (G) being configured to take the retaining projection from the upper end of the upwards path (GS) to the upper end of the downwards path (GB) when the piston reaches a maximum height and the lower end of the guide (G) being configured to take the retaining projection from the lower end of the downwards path (GB) to the lower end of the upwards path (GS) when the piston reaches a minimum height. <EOS>