The present invention discloses a lamp, mounted on a socket when in use, comprising a cap, a housing, and a light source, wherein the cap is adapted to connect to the socket, one of the cap and the housing comprises a tubular body, and the other comprises a cylindrical cavity for accommodating the tubular body, and the tubular body rotates in the cylindrical cavity around an axis of the cap and moves along the axial direction of the cap to effect relative rotation and relative telescopic motion between the cap and the housing. The lamp of the present invention allows both relative rotation and relative telescopic motion between the cap and the housing, therefore facilitating adjustment of the illumination direction, and is adaptable to different types of fittings.