Patent attributes
A metal vapor discharge lamp comprising an arc tube, an airtight tube housing the arc tube, and a base bonded to one end of the airtight tube with use of an adhesive, wherein the airtight tube is covered by a protective tube to improve safety as compared to a case where the protective tube is simply bonded to the base with an adhesive. The protective tube is fixed to the base with a double fall-off prevention structure, and latched to the base when a force including gravity and inertia acts on the protective tube toward the closed end of the protective tube in the axial direction thereof. The above-described structure eliminates the need of arranging the protective wall for securing the safety on the side of a lighting device on which the metal vapor discharge lamp is to be fixed, thereby preventing the lighting device from becoming large in size.
