The arc lamp was the first
lamp used, and was already
in
extensive use by the late 1870s. Arc lamps have
a high
intensity blueish white light, and were used
as
streetlights or to
light up large rooms, like factories.
The
arc lamp consists of two
carbon electrodes, connected
to a
current limiter and a
power source. When the
electrodes are pushed together and then slowly parted, an
electric arc will form through the
ionized air between them.
This arc heats the electrodes to several thousand degrees.
The
electrodes'
tips will glow with an intense light.
The problem with these lamps is that the electrodes must
constantly be readjusted, since the carbon vaporizes.
The first lamps had to be manually adjusted, but later
versions featured automatic adjustment and could even
restart the arc, if it was put out.