If you haven’t heard about the mystery of the nature of light, here is a quick refresher: Light behaves both as a particle and as a wave in different scenarios. While the causes behind this duality are as of yet, unknown, scientists still have been able to explain these natures independently.
Thus, we now know that in terms of its wave nature, light is an electromagnetic wave composed of both electric and magnetic fields, which oscillate in mutually perpendicular directions. And since light behaves like a wave, you can easily understand how it must have a certain frequency and wavelength. So far, we have come across light rays or radiation with frequencies as high as $\mathrm{10^{25}}$ Hz. Such a wide range of frequencies leads to a wide range of properties that different types of light waves have. Thus, it becomes useful to divide all these frequencies into certain bands. In this article, we will discuss one such part of these frequencies, known as the Infrared region.
Quantities in branches of science can take different values. Sometimes, the values they take are defined in steps. For instance, in quantum mechanics, energies in most cases are quantized or digital. They always vary in steps and any value in between these steps is forbidden. The energy of a simple harmonic oscillator is one such example.
On the other hand, a lot of quantities have no such restriction and can take any value. The word spectrum refers to a continuous range of analog values that these quantities can take. It is important to note that a spectrum is continuous, not discrete.
The electromagnetic spectrum is the spectrum or the range of frequencies that electromagnetic waves can have. As we previously mentioned, it can be as high as $\mathrm{10^{25}}$ Hz, and on the low end, even values less than 1 Hz have been observed.
The light that we can see is known as visible light. Among this visible region, red has the lowest frequency. Thus, the term infrared radiation refers to radiation whose frequency is less than that of the red color. Note that this does not mean any radiation with a frequency below 430 THz (red color frequency) is infrared. Instead, the infrared region is bounded between 300 GHz and 430 THz.
Infrared rays are invisible to the naked eye, but they are omnipresent. For example, all objects which are near room temperature emit radiation in the IR range only. Apart from that, the heat emitted from fires is also in the IR range. But the most notable source of IR radiation is sunlight. More than half of the energy that arrives on Earth is in the form of IR rays.
Over the years, the uses of infrared radiation have become too numerous to summarise in a single article. Fields that have extensive uses for IR include scientific, medical, military, commercial, etc.
As previously mentioned, more than half of the sun’s energy arrives in the form of IR rays, which makes it the biggest source of infrared rays on this planet. However, generating infrared radiation is quite easy to generate artificially.
Almost all objects constantly emit infrared radiation, though in most cases, it is too small to have any visible effect. Heating up objects can increase the amount of infrared radiation they emit. When you wring your hand near a hot stove and feel its warmth without touching it, you are feeling infrared radiation. Another way to produce infrared rays is to use LEDs whose band gaps lie in the infrared region, which is around 1.4 eV. This method is most commonly used in the generation of IR rays.
Infrared rays lie below the visible region and thus, are invisible to the naked eye. However, its effects can be felt in the form of heat. This property is commonly used in the therapeutic applications of infrared radiation.
Infrared radiation has energies even less than visible light. This means that their penetrating power is very low. Even a stack of papers that is thick enough can block infrared radiation. The glass used in windows blocks infrared radiation very effectively. On human skin, infrared radiation goes no farther than about 5 mm.
Infrared radiation is quite safe, especially compared to radiation beyond visible light like ultraviolet and X-rays. Note that too much radiation is harmful no matter what kind it is. For instance, since infrared radiation carries heat, overexposure can cause burns.
During the onset of Covid-19, you must have seen an upsurge in the sale of infrared thermometers. These thermometers detect the amount of IR radiation emitted from their targets and can detect temperature highly accurately within a second.
Infrared rays are also used in therapeutic applications for heat massages, muscle relaxation, cellulite treatments, etc.
Infrared radiation can be used to find targets accurately without the need for a line of sight since it can pass through most opaque objects. Night-time vision goggles also make use of infrared rays to generate an image of the user’s surroundings.
Infrared radiation can be used to study celestial objects and highly redshifted portions of space. Further, IR imaging can be used to figure out if electrical components are overheating. Weather forecasting and short-range wireless communications also make use of the IR range.
Infrared rays carry heat and thus, cause objects absorbing them to heat up. Overexposure to infrared radiation is dangerous not only because of heat but also because it affects the eyes, causing damage or even blindness in extreme cases. Thus, industry settings where infrared radiation is common must only be tackled with special infrared-proof goggles.
At the same time, the heating effect of infrared radiation means that it is useful in curing common colds, and fatigues, easing kidney functions, and helping with other forms of pain.
The electromagnetic spectrum is the range of frequencies that electromagnetic radiation can have. Infrared rays are light or electromagnetic waves whose frequencies are lower than that of red light. This corresponds to between 300 GHz and 430 THz. Infrared radiation carries heat and is emitted by almost every single object that is heated up. Black-body radiation at room temperature is in the visible region. Other sources of infrared radiation include natural sources such as the sun and artificial sources like LEDs with band gaps around 1.4 eV.
Infrared radiation is used in scientific, military, and commercial applications like astronomy, target-seeking, night-vision goggles, heat therapy, etc. The most prominent effect of infrared is that of heat, and it can prove dangerous to the eyes upon overexposure.
Q1. Can infrared radiation affect cells, leading to increased cancer risk?
Ans. No. Infrared radiation does not have enough energy to increase the risk of cancer. However, increased temperature of the skin can affect the speed at which DNA repair occurs inside our bodies.
Q2. How do we block infrared rays from the sun?
Ans. A sheet of window glass or plastic is enough to block infrared radiation since it is not energetic enough to pass through these objects.
Q3. Are night-vision and thermal imaging the same?
Ans. No. Thermal imaging captures a map of how heat is distributed over an area. On the other hand, night-vision goggles detect infrared photons and then amplify the signals to generate an image of the user’s surroundings.
Q4. Give an example of how IR is used in short-range communications.
Ans. Most television and AC remotes use infrared radiation to communicate with each other. Even in a longer communication channel, infrared radiation is often used for optical fiber communications.
Q5. If infrared is invisible, how do we see images captured via infrared imaging?
Ans. Different methods exist to make this possible. Thermal imaging can generate a heatmap that can show us outlines of heat changes. Or we can convert signals generated via detecting infrared into an image and apply color depending on intensity.
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