sun- and heat lamp carbon rods differed in chemical composition
Sun- and heat lamp
carbon rods
In order to maintain a quiet and stable arc
discharge, the crater in the tip of the anode had to
be kept more or less in the center of the carbon rod.
This could be achieved by using an anode rod that
was either hollow or filled with a softer type of
carbon. This softer core could also easily be
enriched with small parts of metal in order to alter
the spectrum of the radiation. Adding some iron to
the anode core for example, would increase the
radiation in the ultraviolet region. For
DC-applications the cathode did not need to be
hollow but it had to be fabricated from a type of
carbon that easily could supply a large quantity of
electrons without getting too hot. When operated
with an AC-supply the carbon arc lamp was
equipped with two identical carbon anode rods.