Why do aging sodium lamps sometimes cycle repeatedly on and off?
The sodium vapor pressure is controlled by the temperature of the amalgam reservoirs at the ends of the arc tube. As the lamp ages, the ends of the arc tube get darkened, and they absorb light. This makes them hotter. Therefore, the amalgam reservoirs get hotter. This increases the sodium vapor pressure in the arc tube, leading to different electrical characteristics. When this effect becomes excessive, the arc in the arc tube goes out. The arc tube must cool before the vapor in it is thin enough to restrike an arc. Aging sodium lamps sometimes repeatedly turn on and off as the ends of the arc tubes overheat, then cool off once the arc goes out. If a high pressure sodium lamp repeatedly turns on and off, replacing the bulb with a new one is usually all that is needed. Thermal Conduction from High Pressure Arcs, the Watt per Centimeter Loss When energy is dissipated into an arc, it largely leaves the arc by three mechanisms: 1. Some is used by the cathode and anode fall mechanisms getti
