An optical assembly (12) for lighting sources (L) includes a cup-shaped reflector (14) having a bottom portion (14a) for mounting a light radiation source and a mouth portion (14b) for projecting the light radiation, the mouth portion (14b) having a peripheral rim (140). A light-permeable screen (16) peripherally rests on the rim (140) of the mouth portion (14b) of the reflector (14). Provision is made of a front ring (18) forming a receiving frame for the screen (16) to arrange the screen (16) sandwiched between the reflector (14) and an annular inner side (18a) of the front ring (18). The front ring (18) has a plurality of cusp formations (18b) protruding from the annular inner side (18a) to surround the reflector (14). An annular assembly spring (20) is coupleable to the front ring (18) to urge the reflector (14) and the screen (16) towards the annular inner side (18a) of the front ring (18); the assembly spring (20) has a plurality of cusps having distal ends (200) coupled to the cusp formations (18b) of the front ring (18).