the arc discharge region of the voltage-current characteristic of a gas discharge tube
the electrodes of an arc discharge tube lasted much longer than the carbon rods of a carbon arc sunlamp
Kwarza Bona arc discharge sunlamp
An arc discharge is
characterised by a high
electric current, a low voltage
across the discharge tube and
a much more violent discharge
process compared with that of
a glow discharge. Another
characteristic is the thermal
electron emission of the
cathode. The arc discharge
derives its name from the
phenomena that under
atmospheric conditions a
continuous and horizontal
voltaic arc between two
carbon rods will bend upwards
under the influence of the
upwards flowing hot air around
it. Non-atmospheric
discharges in a tube filled with
a gas like mercury vapour
behave a little differently, depending on the pressure of the gas in the tube. For all arc
discharges it is essential to stabilise the current through the electrodes. Sunlamps
with carbon rods required frequent manual or mechanically automated adjustments
while the rods burned quickly, generally
within a couple of hours. For mercury
vapour arc discharge sunlamps like the
Kwarza Bona sunlamp on display here, it
was sufficient to correctly dimension the
serial ballast since the electrodes would
degenerate only slowly.