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Infrared radiation1, or infrared light, is a type of radiant energy invisible to the human eye. We can detect it as heat, however. All objects in the universe emit infrared radiation to some degree, including the sun and fire.
A type of electromagnetic radiation2, infrared radiation occurs on the electromagnetic spectrum and is produced when atoms absorb and release energy. This spectrum includes X-rays, gamma rays, ultraviolet radiation (sunlight), visible light, microwaves, radio waves, and infrared waves.
Infrared radiation was discovered in 1800 by the British astronomer Sir William Herschel. He directed sunlight through a prism and placed a thermometer outside the red end of the spectrum, noting a high temperature. This is because infrared radiation forces the bonds between molecules to move, releasing energy as heat.
All objects emit some level of thermal energy—even if they feel cold. The hotter an object is, the more thermal energy it emits. This is referred to as a “heat signature”. Animals and humans generate their own heat biologically, but natural objects on earth absorb heat from the sun during the day and release it at night.
We can see infrared radiation due to infrared detection systems, which use sensors to pick up radiation in the infrared portion of the electromagnetic spectrum. These cameras detect the infrared energy emitted and convert it into an electronic signal, which is processed to create an image.
Infrared is a heat-producing wavelength from 0.78 microns to 1000 microns and covers a thermal range of several thousand degrees centigrade to absolute zero Kelvin. Any object that has a temperature above absolute zero Kelvin will emit infrared energy.
This huge temperature range produces different physical characteristics of infrared heat at different frequencies, which include:
The shorter the infrared radiation wavelength, the hotter the heat and greater distance it can travel. This is the principle behind infrared household heaters. Short wave infrared is also very bright compared to medium infrared, which glows, and far infrared, which emits no light.
Infrared radiation is used in a variety of ways, but the most common is heat-sensitive thermal imaging cameras. These are used in night-vision cameras or to sense human and animal body heat patterns, as well as for military use.
Most remote controls operate by sending infrared radiation to an electronic device, such as televisions or projects. Infrared may be used to send signals through fiber optic cables to transmit audio to sound systems or for high-speed internet. It’s also used in household appliances like heat lamps and toasters.
Infrared radiation is necessary for astronomy. Without it, some areas of the sky would look empty and dark, but infrared radiation identifies activity occurring between different celestial bodies, such as nebulas and galaxies. Essentially, astronomy is the detection and study of the infrared radiation of objects in the universe.
But it’s not limited to hot objects. Cool objects also emit infrared radiation, which astronomers can see. By observing cool molecules of gas, astronomers can understand the chemical composition of dust particles.
Heat can be transmitted via conduction, convection, and radiation. Radiation is the fastest transmission and moves at the speed of light. There doesn’t need to be direct contact between an object that needs to be heated and one that’s heating it, like a pan on the stove. Radiant heat is controlled by adjusting the power input.
Infrared radiation is easy to make and control. Fire and light bulbs produce infrared radiation, and we use infrared light in electronics for communications devices.
As mentioned, infrared radiation occurs below the red portion of the spectrum, so its frequencies are lower than the red light that’s visible. This is similar to sound vibrations that humans can’t hear but can feel. Humans can’t see infrared light, either.
Infrared radiation is a form of light that moves in a straight line. This is why a remote control can’t work properly if there are objects in the way of its transmission. This is called line-of-sight transmission, so you need to see the target to transmit infrared light to it.
What are some examples of infrared radiation?
Many household appliances use infrared radiation, including remote controls for electronics devices, infrared cookers, electric heaters, infrared thermometers, and infrared lamps. Infrared radiation is also used in astronomy and in thermal imaging or night-vision cameras.
Is infrared radiation harmful to humans?
Unlike ultraviolet radiation or other types of radiation, infrared radiation isn’t known to cause skin cancer or similar health conditions. Prolonged exposure to infrared radiation can cause irreversible opacity of the eye lens, however, as well as scotoma that can impair vision.
What causes infrared radiation?
Infrared radiation comes from heat or thermal radiation. Any object that has a temperature, even cold objects, radiates infrared radiation.
What color is infrared light?
Infrared light is invisible to the naked eye because it occurs below the red portion of the spectrum. Near-infrared wavelengths become visible as red while red wavelengths look green.
Can you feel infrared radiation?
Infrared radiation can’t be seen by the human eye, but it can be felt. Infrared energy is felt as heat because it interacts with molecules by exciting them, causing them to move faster and increase the internal temperature of the object. Essentially, infrared is just radiated heat.
How hot is infrared?
Infrared spans a wide range of temperatures. For real-world context, sunlight, a well-known source of radiation, has a temperature of 5,780 kelvins (5,510 °C, 9,940 °F) and is composed of near-thermal-spectrum radiation that’s more than half infrared.
We encounter infrared radiation in our daily lives, from sunlight to the heat in our homes to our cooking appliances. This naturally occurring form of radiation isn’t harmful but instead provides virtually endless applications for humans, including thermal imaging and observational astronomy. Though you can’t see infrared radiation, you can sense it around you in the form of heat.
Featured Image Credit: Quality Stock Arts, Shutterstock
Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.
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