What is Infrared?
Our eyes are detectors which are designed to detect visible light waves
(or visible radiation).
Visible light is one of the few types of radiation that can
penetrate our atmosphere and be detected on the Earth's surface.
There are many forms of light (or radiation) which we cannot see with our eyes.
Actually we can only see a very small part of the entire range of radiation
electromagnetic spectrum .
The electromagnetic spectrum includes
gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves.
The only difference between these different types of radiation is their
wavelength or frequency. Wavelength increases and frequency (as well as
energy and temperature) decreases
from gamma rays to radio waves. All of these forms of radiation travel at
the speed of light (186,000 miles or 300,000,000 meters per second in a vacuum).
Infrared radiation lies between the visible and microwave portions of the
electromagnetic spectrum. Infrared waves
have wavelengths longer than visible and shorter than microwaves, and
have frequencies which are lower than visible and higher than microwaves.
Infrared is broken into three categories:
near, mid and far-infrared.
Near-infrared refers to the part of the infrared spectrum that is closest
to visible light and far-infrared refers to the part that is closer to
the microwave region. Mid-infrared is the region between these two.
Infrared view of a melting ice cube
Infrared view of a microwaved burrito
Old Faithful in the infrared
The primary source of infrared radiation is heat or thermal radiation.
This is the radiation produced by the motion of atoms and molecules in an object.
The higher the temperature, the more the atoms and molecules move and the more
infrared radiation they produce.
Any object which has a temperature i.e. anything above absolute zero
(-459.67 degrees Fahrenheit or -273.15 degrees Celsius or 0 degrees Kelvin),
radiates in the infrared. Absolute zero is the temperature at which all
atomic and molecular motion ceases. Even objects that
we think of as being very cold, such as an ice cube, emit infrared.
When an object is not quite hot enough to radiate visible light, it will emit
most of its energy in the infrared.
For example, hot charcoal may not give off light but it does emit infrared
radiation which we feel as heat.
The warmer the object, the more infrared radiation it emits.
Courtesy of Meditherm
Humans, at normal body temperature, radiate most strongly in the infrared at a
wavelength of about 10 microns (A micron is the term commonly used in
astronomy for a micrometer or one millionth of a meter). This is the case for
most warm-blooded animals. Cold-blooded animals, such as reptiles, will
take on the temperature of their environment and are more difficult to detect
in the infrared, unless compared to a cooler or warmer background.
Cold-blooded lizard in a warm human hand
We experience infrared radiation every day.
The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is
infrared. Although our eyes cannot see it, the nerves in our skin can feel
it as heat. The temperature-sensitive nerve endings in your skin
can detect the difference between your inside body temperature and your
outside skin temperature.
We also commonly use infrared rays when we operate a television remote.