| 摘要 |
PROBLEM TO BE SOLVED: To prevent an arc jump, and to prevent a drop of a lamp voltage and degradation of illuminance. SOLUTION: A superposing operation for superposing a pulse current on a lamp current applied to a high-pressure discharge lamp 12 only for a predetermined period, and a superposition stopping operation for stopping the superposition of the pulse current only for a predetermined period are alternately repeated. When the superposing operation is continued, the tip of a cathode electrode 12c is developed into a projecting form, and the lamp voltage gradually drops. Then, the superposing operation is switched over to the superposition stopping operation. Hence, the development of the cathode electrode 12c and the drop of the lamp voltage are restrained to keep the lamp lit. Thereafter, when the superposition stopping operation is continued, the tip of the cathode electrode 12c is consumed by evaporation of tungsten and the arc jump tends to occur. Then, the superposition stopping operation is switched over to the superposing operation to grow the cathode electrode 12c again. COPYRIGHT: (C)2004,JPO |
