Kazutaka Koyama

D. C. Operation of High-Pressure Sodium Lamps with High Color Rendering

During D.C. operation of high-pressure sodium lamps, it has been experimentally found that cataphoresis does not occur when PNA>5.6I1a• L/d 2+0.5, where PNA is the pressure of sodium [kPa], Ila is the lamp current [A], L is the distance between the pair of electrodes, and d is the diameter of the lamp bulb. Therefore , high-pressure sodium lamps with high color rendering do not exhibit cataphoresis, because they satisfy the above condition. However , high-pressure sodium lamps with high color rendering suffer from another problem the color temperature of the lamp is scattered for individual lamps of the same type. This problem can be solved by controlling the lamp voltageVia and the lamp current I la so that a• Vla+b• Ila=constant, where a and b are constants. High—pressure sodium lamps with high color rendering operated under those conditions avoid cataphoresis and have no deviation in color temperature.