A luminaire includes a base, a light-emitting unit, and a lamp cover. The base includes a first tube part, a second tube part having an inner diameter smaller than that of the first tube part, and a joint part connected between the first and second tube parts. An inner flow path is defined by at least the first tube part, the joint part, and the second tube part in a coaxial manner. The lamp cover is fixed on the base for covering the light-emitting unit. As such, air heated by the light-emitting unit flows out of the inner flow path to thereby allow cold air to be sucked into the inner flow path.