Glow discharge sunlamp
of unknown origin
GLOW-DISCHARGE
A glow discharge is
characterised by a low current,
a high voltage and a relatively
calm discharge process. The
temperature of the cathode will
hardly rise under the quiet but
continuous bombardment with
ions which free just enough
electrons to keep the glow
discharge going on. Due to
this behaviour the glow
discharge is also known as
cold-cathode emission and it is
this type of discharge that is
used in the bent glass tubes
that form the well known
coloured neon signs that
decorate our cities, an
application introduced by
Georges Claude in 1911. A
glow discharge was also used
in some types of sunlamps. A tube of
quartz glass was filled with mercury
vapour and the serial ballast was
dimensioned in such a way that it limited
the current through the tube to the level of
a glow discharge. For a glow discharge
the output of ultraviolet radiation
measured per meter tube is relatively low,
compared with the output of an arc
discharge. Partly this was compensated
by the use of relatively long tubes, as
with the glow discharge sunlamp of
unknown origin on display here.
