| 摘要 |
PURPOSE:To prevent reduction of the luminous efficiency by forming the coldest part at the tip of the return part of a U-shaped discharge lamp by setting the ratio A/B related to the cross-sectional area A of the discharge path in said return part and the cross-sectional area B of the discharge path of the bulb part to 2-10, and controlling the mercury vapor pressure in the lamp within the optimum operation range. CONSTITUTION:As the ratio A/B related to the cross-sectional area A of the discharge path in the return part 4 of a U-shaped discharge lamp and the cross- sectional area B of the discharge path of the bulb part is set to 2-10, the local load onto the return part can be lightened. Therefore, the temperature at the part T in said return part is kept lower than the temperature in other parts. Therefore, the mercury in the bulb gathers onto the inner wall of the part T supposed to be the coldest part, during the time when the lamp comes on, and the mercury vapor pressure in the lamp is determined according to the temperature at the part T. In the lamp having the constitution proposed by the present invention, the mercury vapor pressure in the lamp can be maintained at the optimum value. |
