The
low pressure sodium lamp is
regarded as the most
efficient of
all known
lightsources. It has low
running costs and
long
life time(about 18,000 hours). It is much used in
street lights and is
easily recognized
by it's
intense orange light. The
fact that the
light is
monochromatic limits the use of this
lightsource to applications
where
colour recognition isn't
important
The LPS lamp consists of a
arc tube made from
sodium resistant
glass. The
tube is
filled with a
neon-
argon mix and
sodium. When the lamp
is
energized this
gasmix starts
ionizing. The heat from this
procces
vaporizes the
sodium and starts to emit
visible light. Outside
the arc tube is another layer of glass. This is
coated on the inside
with
heat reflective indium oxide, this keeps the
heat
inside the lamp so the
sodium vaporizes faster. The LPS lamp
often
needs several minutes to reach the
optimum operating temperature.