A mounting structure for lighting devices , the structure comprising: - a light generator (L) carrier portion comprising an elongate body extending along a longitudinal axis (X10), and - a ring portion fitted onto the elongate body of the carrier portion , wherein: - one of the elongate body of the carrier portion and the ring portion carries at least one tooth member (111; 123) protruding towards the other of the elongate body of the carrier portion and the ring portion , - the other of the elongate body of the carrier portion and the ring portion comprises at least one arch-shaped engagement formation (121; 124) for said at least one tooth member (111; 123), wherein the carrier portion and the ring portion are restrained from mutual displacement along said longitudinal axis (X10) by the at least one tooth member (111; 123) engaging the at least one arch-shaped engagement formation (121; 124) with the at least one tooth member (111; 123) displaceable along the at least one arch-shaped engagement formation (121; 124) wherein the elongate body of the carrier portion is rotatable relative to the ring portion around said longitudinal axis (X10) of the elongate body of the carrier portion , characterized in that the at least one arch-shaped engagement formation (121; 124) comprises a sculptured surface (1210; 1240) providing a plurality of engagement positions for the at least one tooth member (111; 123), the engagement positions in said plurality of engagement positions angularly spaced around said longitudinal axis (X10) of the elongate body of the carrier portion wherein the ring portion is rotatable step-wise relative to the elongate body of the carrier portion around said longitudinal axis (X10) of the elongate body of the carrier portion . - a light generator (L) carrier portion comprising an elongate body extending along a longitudinal axis (X10), and - a ring portion fitted onto the elongate body of the carrier portion , - one of the elongate body of the carrier portion and the ring portion carries at least one tooth member (111; 123) protruding towards the other of the elongate body of the carrier portion and the ring portion , - the other of the elongate body of the carrier portion and the ring portion comprises at least one arch-shaped engagement formation (121; 124) for said at least one tooth member (111; 123), wherein the carrier portion and the ring portion are restrained from mutual displacement along said longitudinal axis (X10) by the at least one tooth member (111; 123) engaging the at least one arch-shaped engagement formation (121; 124) with the at least one tooth member (111; 123) displaceable along the at least one arch-shaped engagement formation (121; 124) wherein the elongate body of the carrier portion is rotatable relative to the ring portion around said longitudinal axis (X10) of the elongate body of the carrier portion , characterized in that the at least one arch-shaped engagement formation (121; 124) comprises a sculptured surface (1210; 1240) providing a plurality of engagement positions for the at least one tooth member (111; 123), the engagement positions in said plurality of engagement positions angularly spaced around said longitudinal axis (X10) of the elongate body of the carrier portion wherein the ring portion is rotatable step-wise relative to the elongate body of the carrier portion around said longitudinal axis (X10) of the elongate body of the carrier portion . <EOS>