Characteristics of Fluorescent Lamps in Direct Current Operation under High Ambient-Temperature Condition.

Abstract

Characteristics of a fluorescent lamp in direct current operation under high ambient-temperature conditions are investigated for application to the back-light system. It is shown that the problems relating to direct current operation of fluorescent lamps, which are light output reduction and short electrode life due to cataphoresis, can be solved by operating the lamp in such a high ambient-temperature obtained in closed fixtures of back-light systems. When the wall temperature was kept to be approximately 80°C, the total light output was approximately 6% higher in direct current operation than in alternate current operation. This may be due to the fact that the mercury atom density in the positive column is closer to the optimum value in direct current operation than in alternate current operation, when the lamp is operated in high ambient-temperature. The electrode life in direct current operation is as long as that in alternate current operation. The high mercury atom density in the cathode region due to cataphoresis may be effective to improve electrode life because of reducing cathode fall voltage.