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The common household electric bulb is an
example of an incandescent lamp. A close look at one will tell you
two things at a glance. One, that it is sealed and secondly that
there is a filament inside it. The coiled filament that you see
inside is made of the metal tungsten and the bulb is filled with a
gas and then sealed. A gas that will not react with tungsten is
chosen for filling. The gas used is a combination of nitrogen and
argon.
Bulbs of varying wattages giving out
varying levels of brightness are available. This is done mainly by
varying the nitrogen argon combination to achieve the desired level
of brightness and wattage.
Why does the bulb glow?
When electric current passes through the filament, it gets
heated to a temperature of about 3000º Celsius. As a result of the
high temperature, the tungsten filament begins to glow and emit
light.
The electric bulb is based on the principle
of incandescence. This principle covers solids and gases that emit
visible light when exposed to high temperature. The color of light
given out by a material will differ from material to material. This
principle was first demonstrated in 1812 by Sir Humphrey Davy, a
British chemist. He demonstrated the principle by heating platinum
strips using electricity. British inventor Frederick de Mulleins
demonstrated the principle of incandescence using a lamp that heated
platinum wires using powdered charcoal and provided illumination as
a result. He was awarded a patent in 1841. In the meanwhile, vacuum
pumps had been invented and they were being used to make evacuated
glass bulbs with carbon filaments that provided better illumination.
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The usual answer one gets to the
question “Who invented the light bulb?” is Thomas Alva Edison.
The credit for the invention of the modern light bulb is shared
by two people. Sir Joseph Wilson Swan, an English scientist,
invented the first practical light bulb in 1878. The same device
was also invented independently by Edison a year later than Sir
Joseph Wilson Swan. The reason why Edison receives more credit
is that he also invented the electrical infrastructure needed to
make a practical lighting system.
William David Coolidge, an American
engineer developed a process in 1908 with which tungsten could
be drawn into wires. Once this was possible, the ductile
tungsten, which has the highest melting point among metals, was
used in light bulbs. The year 1911 saw the use of tungsten
filaments and the result was better light bulbs.
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Thomas Alva Edison |
Many other improvements have followed.
Coiled filaments were used in 1913 and the use of inert gas inside
the bulbs has produced more efficient bulbs. Earlier, only nitrogen
was used and later a mixture of nitrogen and argon was used.
The quality of light emitted by the bulbs
has also been varied by giving the interior of the glass bulbs a
coating of hydrofluoric acid. This improvement was effected in 1925
and gave us softer and diffused lighting. |
