A lamp includes a tube, a reflector, at least one illuminator unit, at least one radiator and two connectors. The tube is made of a transparent material. A reflector is disposed in the tube. The illuminator unit includes at least one light-emitting diode for emitting light. The radiator includes a first reduced portion inserted in the tube, a second reduced portion located opposite to the first reduced portion and fins for dissipating heat generated by the light-emitting diode. The first reduced portion of the radiator is formed with a face for supporting the illuminator unit so that the light-emitting diode can cast the light to the reflector that can reflect the light. The connectors are connected to the illuminator unit for conducting electricity to the illuminator unit from a power supply.