Fluorescent lamps and low pressure sodium lamps

Both the fluorescent lamp and the low pressure sodium lamp are based on the same type of discharge, namely the low pressure metal/rare-gas discharge. The paper deals with recent advances and possible future developments for both types of lamps. For the fluorescent lamp, recent advances include a better understanding of the discharge processes, the introduction of narrow emission band phosphors, the use of more efficient narrower diameter discharges and improvements in the control of the mercury vapour pressure. Possible future developments include the more general use of electronic control gear, electrodeless discharge lamps, and more compact lamps realised, e.g. by using a recombination structure in the discharge vessel. For the low pressure sodium lamp recent advances include a better understanding of the discharge processes, improvements in the thermal insulation of the discharge tube, leading to better arc voltage control, and a modified current waveform leading to an improved combination of lamp and control gear. Possible future developments are likely to be similar to those for the fluorescent lamp, e.g. a further introduction of electronic control gear, and also a further miniaturisation of the lamp.