Abstract: A sight assembly may include a body or chassis having a channel configured and dimensioned to fit on and secure to the rib or rail of the barrel of a firearm. A pair of opposing pivotable cams are configured to secured against opposite sites of the rail using screws or other members to provide a biasing force against each cam. A light source directs light through an optical housing supported on the chassis and through a lens toward the user, such that the light may be visible only when the firearm is properly aimed.