<p>A bulb (10) has a tubular shape having a side peripheral wall (10a) and end walls (10b, 10c) at opposite ends of the bulb. In the end walls (10b, 10c) are formed small openings having a diameter less than the outer diameter of the bulb (10). On the inner surfaces of those walls of the bulb (10) which include the end walls (10b, 10c), there is formed a fluorescent material layer. Leads (31) are inserted through stems for sealing the openings in the opposite ends of the bulb (10). Electrodes (33) are connected to those ends of the leads (31) which are on the inner sides of the bulb (10).</p>
