A lighting system includes a fluorescent lamp 4 and a main body 1 for attaching the fluorescent lamp 4 thereto. The main body 1 is provided with a socket assembly 6 for the attachment of the fluorescent lamp 4, and an electronic ballast 7 for operating the fluorescent lamp 4 at dimmed levels (as well as at the full light level). The fluorescent lamp 4 is composed of a discharge tube formed of four U-shaped glass tubes that are connected together to form a square in plan view. Each glass tube has an inner diameter of 13.5 mm, and the discharge tube is filled with a rare gas containing neon and argon (at 50:50 ratio by volume).