Basically, an electric current is a displacement of small electric charges. The carriers
of such charges are negatively charged electrons who, together with a nucleus of
evenly strong but positively charged protons and chargeless neutrons, form atoms,
the building blocks of all matter that our world consists of.
For a current to flow, it requires a medium with electrons that, under the influence of a
potential difference, can be forced to travel from their own nucleus of protons and
neutrons to adjacent nuclei. Solids with this capability are said to be conductive and
therefore called electric conductors. Copper is the best known electric conductor but
for the construction of heat lamps, conductors that can withstand higher temperatures
were more suitable. A sufficient high current through a conductor will cause a rise in
temperature of the conductor, resulting in the emission of invisible infrared radiation.
At higher temperatures the conductor may eventually start glowing, which is no other
thing than emitting light.
For the construction of a sunlamp, an electric discharge was the most effective
source of ultraviolet radiation. An electric discharge was obtained by generating a
potential difference between two electric conductors (electrodes) that were
separated from each other by air or another gaseous medium. A sufficiently high
potential difference between the electrodes caused a fierce electric current between
the electrodes (a voltaic arc), accompanied by a strong electromagnetic radiation.
From itself such electromagnetic radiation could already contain a significant high
quantity of ultraviolet radiation and by choosing the proper composition for the
medium and the electrodes the amount of ultraviolet radiation could be increased
even further.