1. INFRARED RADIATION
A short history
What is it?
Application of infrared rays in
our life

2. Short history
The discovery of infrared radiation is ascribed to
William Herschel, the astronomer, in the early
19thcentury. He used a prism to refract light
from the sun and detected the infrared beyond
William Herschel
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 prism
calorific rays. The term of infrared did not
appear until late in the 19th century.

3. What is the
infrared
radiation?
Infrared radiation (IR) is an electromagnetic radiation with a
wavelength longer than that of visible light.
Infrared radiation includes most of the thermal radiation emitted
by objects near room temperature.
Microscopically, IR light is typically emitted or absorbed by
molecules when they change their rotational vibrational
movements.

4. Much of the energy from the Sun arrives on Earth in the form
on infrared radiation. Sunlight at zenith provides an irradiance
of just over 1 kilo watt per square meter at sea level. Of this
energy, 527 watts is infrared radiation, 445 watts is visible
light, and 32 watts is ultraviolet radiation.
The balance between absorbed and emitted infrared radiation
has a critical effect on the Earth’s climate

5. Practical
application
Infrared light is used in
industrial, scientific, and
medical
application. Infrared imaging
cameras are used to detect
heat loss in insulated
systems, observe changing
blood flow in the skin, and
overheating of electrical
apparatus.

6. In astronomy,
imaging at infrared
wavelengths allows
observation of
objects obscured
by interstellar dust.
Night-vision devices using infrared
illumination allow people or
animals to be observed without the
observer being detected

7. The Earth as infrared emitter
The Earth’s surface and the clouds absorb
visible and invisible radiation from the Sun
and re-emit much of the energy as infrared
back to the atmosphere. Certain substances
in the atmosphere, chiefly cloud droplets
and water vapor, but also carbon dioxide,
methane, nitrous oxide, absorb this infrared
and re-radiate it in all directions including
back to Earth. Thus the greenhouse effect
keeps the atmosphere and surface much
warmer than if the infrared absorbers were
absent from the atmosphere.

8. Infrared and greenhouse effect

9. Curiosities
• Some animals (snakes, owls) can see
infrared rays. This ability helps them to find
food faster.
• Infrared rays act deeply in our tissues. That’s
why they are used as a method for losing
weight. It is known as the most non-evasive
therapy even for treating cancer.