A lamp including a first housing, a second housing assembled with the first housing to form a housing assembly and a bulb base is provided. The second housing includes a first sidewall and a second sidewall perpendicularly connected to the first sidewall. The first sidewall has a first stop portion extending along a normal direction. The bulb base is inserted into a first opening of the housing assembly to be assembled to the housing assembly. The bulb base has a second opening, multiple catches arranged on an outer sidewall of the second opening in a circumference direction and a second stop portion. The second stop portion disposed on the catches is located on a rotation path of the first stop portion when the bulb base rotates relative to the housing assembly for limiting a rotation angle between the housing assembly and the bulb base.