Abstract: A lighting device comprises a lamp housing, a lighting body provided in the lamp housing and having a working voltage of direct-current 3V-36V, and a lamp base detachably connected with the lamp housing and in detachable electrical connection the lighting body. The lamp housing and the lamp base are made from a plastic material. A lamp string comprises a lamp wire and lighting devices electrically connected thereto. The lighting device and the lamp string are more convenient to assemble, do not require vacuum or filling of an inert gas. The lighting body, when damaged, can be disassembled and replaced at any time, with low production, maintenance and using costs. Using the plastic lamp base and lamp housing makes the lighting device more durable. No adapter is provided inside the lighting device, so that the internal structure of the lighting device is more simplified, and it is safer to use.