The invention relates to a bulb, which comprises a lamp housing, a light source and a lamp head, wherein the lamp housing comprises a first end surface and a second end surface, wherein the first end surface and the second end surface are opposite, the light source is positioned on the first end surface of the lamp housing and is in heat connection with the lamp housing, the lamp head is connected onto the second end surface of the lamp housing, the light source is electrically connected with the lamp head, a communicated heat radiation passage is arranged on the lamp housing, the heat radiation passage is a through hole with the sealed periphery and extends in a direction from the first end surface to the second end surface, and the convection and the circulation of the air can be accelerated.