A lamp is provided. The lamp may include: a housing, a guide rail clamp, arranged on the housing, the guide rail clamp including a first sliding block and a second sliding block that are arranged at intervals, the first sliding block being detachably arranged on the housing, a connecting component, the connecting component being in connection with the first sliding block to fix the first sliding block on the housing, the connecting component forming an assembling unit jointly with the first sliding block, a positioning structure, including a positioning piece and a positioning hole, the positioning piece being arranged on one of the housing and the assembling unit, the positioning hole being arranged on another of the housing and the assembling unit, and the positioning piece being inserted into the positioning hole when the assembling unit moves to an assembling position.