Glow-to-arc transition in mercury-free HID lamps: Cathode phenomena and salt evaporation model

Summary form only given, as follows. The time scale for development of high-intensity discharge (HID) plasmas ranges from 100s ns at the breakdown phase to 10s ms in the arc regime, and to seconds for fully quasi-steady state operation. The breakdown phase is dominated by space charge effects, while the high density plasma in the arc regime is essentially quasi-neutral where ambipolar transport dominates. Coincident to the formation of the arc, heating of the dose of metal halides such as NaI, ScI3 and ZnI2, adds their vapor to the system which also adds additional complexity to the startup sequence of the lamp.