INFRARED (IR):-This light is electromagnetic
radiations with longer wavelengths than those of visible
light, extending from the nominal red edge of the visible
spectrum at 700 nanometer (nm) to 1 mm. Wavelengths of these rays corresponds to a frequency range of
approximately 430 THZ down to 300 GHz, and includes most of the
thermal radiation emitted by objects near room temperature. Infrared light
is emitted or absorbed by molecules when they change their rational-vibrations movements.
It was first discovered in 1800 by astronomer William Herschel. Slightly
more than half of the energy from the Sun arrives on Earth in the form of
infrared radiation. The balance between absorbed and emitted infrared radiation
has a critical effect on Earth's climate.
History of Infrared:-The discovery of this radiation is ascribed to William
Herschel, the astronomer, in the early 19th century. He published his results
in 1800 before the Royal Society of London. He used a prism to refract light
from the sun and detected the infrared, beyond the red part
of the spectrum, through an increase in the temperature recorded on a thermometer.
He was surprised at the result and called them "Calorific Rays". The
term 'Infrared' did not appear until late in the 19th century.
Applications
of infrared:-
· NIGHT VISION:-
Infrared rays is used
in night vision equipment when there is insufficient visible light to
see. Night vision devices operate through a process involving the
conversion of ambient light photons into electrons that are then amplified by a
chemical and electrical process and then converted back into visible
light. Infrared light sources can be used to augment the available ambient
light for conversion by night vision devices, increasing in-the-dark visibility
without actually using a visible light source.
The use of these
lights and night vision devices should not be confused with thermal
imaging, which creates images based on differences in surface temperature by
detecting infrared radiation that emanates from objects and their surroundings.
· THERMOGRAPHY:-
Infrared radiation
can be used to determine the temperature of objects. This is termed
thermography, or in the case of very hot objects in the NIR or visible it is
termed pyrometry. Thermal imaging is mainly used in military and
industrial applications but the technology is reaching the public market in the
form of infrared cameras on cars due to the massively reduced production costs.
Thermo graphic
cameras detect radiation in the infrared range of the electromagnetic
spectrum and produce images of that radiation. Since these radiation is emitted
by all objects based on their temperatures, according to the black body radiation
law, thermography makes it possible to "see" one's environment with
or without visible illumination. The amount of radiation emitted by an object
increases with temperature, therefore thermography allows one to see variations
in temperature.
· Climatology:-
In the field of
climatology, atmospheric infrared radiation is used to monitored and detect
trends in the energy exchange between the earth and the atmosphere. These
trends provide information on long-term changes in Earth's climate. This is one
of the primary parameters studied in research into global warming, together
with solar radiation. A pyrometer is utilized in this field of research to
perform continuous outdoor measurements.
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