Infrared radiation (IR), or infrared light, is a type of radiant energy that’s invisible to human eyes but that we can feel as heat. All objects in the universe emit some level of IR radiation, but two of the most obvious sources are the sun and fire.

Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelength longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from the nominal red edge of the visible spectrum around 700 nanometers (frequency 430 THz), to 1 millimeter (300 GHz). (although the longer IR wavelengths are often designated rather as terahertz radiation). Black body radiation from objects near room temperature is almost all at infrared wavelengths. As a form of electromagnetic radiation, IR propagates energy and momentum, with properties corresponding to both those of a wave and of a particle, the photon.

A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) light.


Wavelength is the distance between identical points (adjacent crests) in the adjacent cycles of a waveform signal propagated in space or along a wire. In wireless systems, this length is usually specified in meters (m), centimeters (cm) or millimeters (mm). In the case of infrared (IR), visible light, ultraviolet (UV), and gamma radiation (γ), the wavelength is more often specified in nanometers (nm), which are units of 10-9 m, or angstroms (Å), which are units of 10-10 m. the wavelength is the spatial period of a periodic wave—the distance over which the wave’s shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossing, and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The inverse of the wavelength is called the spatial frequency. Wavelength is commonly designated by the lambda (λ). The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.

The wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown.

visible light

Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz).

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.


The nanometre (international spelling as used by the International bureau of weights and Measures; SI symbol: nm) or nanometer is a unit of length in the metric system, equal to one billionth (short scale) of a metre (0.000000001 m). One nanometre can be expressed in scientific notation as 1×10−9 m, and as 1/1000000000 metres.

one nanometric carbon nano tube, photographed with Scanning Tunneling Microscope


The millimetre (international spelling; SI unit symbol mm) or millimeter is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand millimetres in a metre. There are ten millimetres in a centimetre.

One millimetre is equal to 1000 micrometres or 1000000 nanometres. Since an inch is officially defined as exactly 25.4 millimetres, a millimeter is equal to exactly 5127 (≈ 0.03937) of an inch.

Ruler with millimetre and centimetre marks

Terahertz radiation

Terahertz radiation is typically understood to be electromagnetic radiation in the frequency range from roughly 0.1 THz to 10 THz, corresponding to wavelengths from 3 mm down to 30 μm. Such frequencies are higher than those of radio waves and microwaves, but lower than those of infrared light. As the wavelengths are in the range of 0.03 mm to 3 mm, and often below 1 mm, terahertz radiation is also sometimes called submillimeter radiation. Also, at least the higher-frequency part of the terahertz region may also be called the far infrared.

Terahertz radiation – also known as submillimeter radiationterahertz wavestremendously high frequency (THF), T-raysT-wavesT-lightT-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz), although the upper boundary is somewhat arbitrary and is considered by some sources as 30 THz. One terahertz is 1012 Hz or 1000 GHz. Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.01 mm = 10 µm. Because terahertz radiation begins at a wavelength of around 1 millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared, and can be regarded as either.


energy is the quantitative propertity that must be transferred to a body or physical system to perform work on the body, or to heat  it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metres against a force of one newton.

The Sun is the source of energy for most of life on Earth. It derives its energy mainly from nuclear fusion in its core, converting nuclear binding energy to other forms such as radiant energy as protons are combined to form helium. This energy is transported to the sun’s surface then released into space mainly in the form of radiant (light) energy.


Photon, also called light quantum, minute energy packet of electromagnetic radiation. The energy of a photon depends on radiation frequency; there are photons of all energies from high-energy gamma- and X-rays, through visible light, to low-energy infrared and radio waves. All photons travel at the speed of light. Considered among the subatomic particles, photons are bosons, having no electric charge or rest mass and one unit of spin; they are field particles that are thought to be the carriers of the electromagnetic field.

The photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always move at the speed of light in vacuum, 299792458 m/s (or about 186,282 mi/s). The photon belongs to the class of bosons.

Photons are emitted in a threaded laser beam


Radio Waves

Radiant Energy

Electromagnetic Field

Electromagnetic radiation

Ultraviolet–visible spectroscopy

Bhanu Pratap Singh


View all posts by Bhanu Pratap Singh →

Leave a Reply

Your email address will not be published. Required fields are marked *

error: Content is protected !!