An illuminating device includes a heat-dissipating shroud, a heat-dissipating module, an upper cover module and a lower cover module. The heat-dissipating module includes a light source, a substrate, a heat-conducting element and heat-dissipating blades. The upper cover module includes an upper cover, a light sensor and a protective cover. The lower cover module includes a lower cover, a transparent shroud and a transformer. The heat-dissipating shroud is assembled above the heat-dissipating blades of the heat-dissipating module. A top surface of the heat-dissipating shroud is provided with heat-dissipating holes. A space of a suitable height is generated between the top surface of the heat-dissipating shroud and the heat-dissipating blades of the heat-dissipating module to act as a heat concentration chamber. A gap is formed between the bottom of the heat-dissipating shroud and the top surface of the upper cover of the upper cover module.