What is Infrared (IR)? (2024)

Infrared (IR) is a type of electromagnetic radiation that has longer wavelengths than visible light, making it invisible to the human eye. It falls just beyond the red portion of the visible spectrum, hence its name meaning “below red.” Infrared radiation can carry heat and is commonly emitted by objects like the sun, light bulbs, and even living beings.

This radiation is used in various applications, including remote controls, night-vision devices, and thermal imaging cameras, as well as in telecommunications and some scientific research

Characteristics of Infrared Radiation

Infrared radiation (IR) has several characteristics that make it important in many scientific and practical applications:

1. Wavelength Range: Infrared covers the wavelength range from about 700 nanometers (nm) to 1 millimeter (mm). This range falls just beyond the red part of the visible light spectrum and is typically divided into near, mid, and far infrared.

2. Heat Emission: Infrared radiation is often associated with heat, as it is emitted by objects based on their temperature. The warmer an object is, the more infrared radiation it emits, which is why thermal imaging cameras can detect humans and animals in the dark.

3. Transmission through Atmosphere: Infrared radiation can travel through fog, dust, and smoke more effectively than visible light, which is why it is used in certain imaging technologies.

4. Absorption and Emission by Materials: Many materials absorb and emit infrared radiation, which can be used to study the properties of these materials or to detect them in a given environment.

5. Wave and Particle Nature: Like all electromagnetic radiation, infrared exhibits both wave-like and particle-like properties. It can be described as waves of energy or as streams of particles called photons.

6. Invisibility: Since its wavelengths are longer than those of visible light, infrared is invisible to the human eye. However, some IR wavelengths can be perceived as heat by skin.

7. Applications: Infrared has a wide range of applications including in remote controls, security systems, astronomy, weather forecasting, heating, wireless communication, and medical imaging, among others.

Infrared Radiation Wavelength and Frequency

We already know that the wavelength of infrared radiation is between 700 nm to 1 mm, which is between the red limit of the visible spectrum. But the following is the classification of bands based on the spectral range 1µm and 50µm:

• 1µm to 3µm, which is known as Band I or Short Wave Infrared
• 3µm to 5µm, which is known as the Band II or Middle Wave Infrared
• 8µm to 14µm, which is known as the Band III or Long Wave Infrared

Properties of Infrared Waves

1. Wavelength Range

Infrared waves have wavelengths longer than those of visible light. They span from approximately700 nanometers (nm)(near the red edge of visible light) up to1 millimeter. While we can’t see them directly, certain IR wavelengths can be detected under specific conditions.

2. Thermal Radiation

Most of the thermal radiation emitted by objects near room temperature falls within the infrared range. This property is essential for applications likethermal imagingandnight vision.

3. Wave-Particle Duality

Like all electromagnetic radiation, IR exhibits both wave-like and particle-like behavior. IR photons carry energy and interact with matter, leading to phenomena such as absorption and emission.

4. Categories of Infrared

IR is divided into five categories based on wavelength:

Near-Infrared (NIR): Ranges from 700 nm to about 1400 nm. Used in optical communication and remote sensing.

Short-Wavelength Infrared (SWIR): Extends from 1400 nm to 3000 nm. Useful for material analysis.

Mid-Wavelength Infrared (MWIR): Spans 3000 nm to 8000 nm. Applied in thermal imaging and gas detection.

Long-Wavelength Infrared (LWIR): Covers 8000 nm to 15000 nm. Commonly used in surveillance and medical imaging.

Far-Infrared (FIR): Encompasses 15,000 nm to 1 mm. Relevant for astronomy and molecular vibrations.