A lamp includes a heat dissipater having a base and an engaging member. The base includes a first air guiding portion and a fixing portion. The engaging member is mounted to an outer periphery of the base. A second air guiding portion is formed between the engaging member and the base. A lighting element is mounted to the base of the heat dissipater. A housing is engaged with the engaging member of the heat dissipater. The housing and the heat dissipater together define a compartment in communication with the first and second air guiding portions. A cooling fan is mounted to the fixing portion of the base. A circuit board is mounted in the compartment and electrically connected to the lighting element and the cooling fan. The circuit board is electrically connected to an electrically conductive member having an end extending out from the housing.