Wavelength
The distance between two consecutive crests, in metres. Across the spectrum it runs from over 100 kilometres down to less than a millionth of a billionth of a metre.
Home Electromagnetic Spectrum
Every Kind of LightThe Electromagnetic SpectrumAll 7 Types of Waves, Wavelengths, Uses & History
From radio waves hundreds of kilometres long to gamma rays smaller than an atom, every kind of light is the same wave travelling at the same speed. The only thing that changes is the wavelength — and the energy it carries.
The electromagnetic spectrum is the complete range of electromagnetic radiation arranged by wavelength and frequency. From longest wavelength to shortest, its seven bands are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All electromagnetic waves travel at the speed of light (299,792,458 m/s in a vacuum) and are connected by two equations: c = f × λ and E = h × f. As wavelength decreases, frequency and energy increase. Visible light, the only band humans can see, spans just 380 to 700 nanometres — a tiny fraction of the whole spectrum.
Definition
What is the electromagnetic spectrum?
The electromagnetic spectrum is the entire collection of electromagnetic waves, organised by wavelength and frequency. It runs from the longest radio waves, which can measure hundreds of kilometres from one crest to the next, down to gamma rays with wavelengths smaller than a single atom. Every one of them is the same phenomenon, differing only in scale.
An electromagnetic wave is a self-sustaining ripple of electric and magnetic fields. The electric field and the magnetic field oscillate at right angles to each other, and both oscillate at right angles to the direction of travel. That perpendicular geometry makes every electromagnetic wave a transverse wave, never a longitudinal one. Because these waves are made of fields rather than vibrating matter, they need no medium and cross the complete vacuum of space — which is why sunlight reaches us across 150 million kilometres of emptiness while sound cannot cross even a small vacuum.
Every electromagnetic wave travels at the same speed in a vacuum: approximately 299,792,458 metres per second, written as c. A radio wave and a gamma ray leaving the same point together would race through space side by side at exactly that speed. What separates them is not how fast they move but how tightly their energy is packed.
The bands have no sharp edges. Radio, microwave, infrared and the rest are human labels for convenient regions; in reality each blends smoothly into the next, and textbook boundaries differ slightly between sources.
Interactive
Drag across the whole spectrum
One slider, nineteen orders of magnitude. Every reading below is computed live from the two equations that govern the spectrum — so you can watch wavelength, frequency and photon energy trade off against each other in real time.
This interactive explorer needs a browser with canvas support. The band table and the written sections below cover the same ground.
BandVisible lightNon-ionizing
Wavelength λ550 nmabout the size of a bacterium
Frequency f545 THzf = c / λ
Photon energy E2.25 eVE = h f
Typical use: Human vision, photography
Tap a band name to jump straight to it. Inside the visible band the wave is drawn in its true spectral colour.
The Physicsλ f E
Wavelength, frequency and energy are locked together
Three properties fix where any wave sits on the spectrum, and they are bound so tightly that knowing one gives you the other two.
Frequency
Cycles passing a fixed point each second, in hertz. Radio waves may cycle a few thousand times a second; gamma rays more than ten billion billion times.
Energy
How much energy each particle of light — each photon — carries, usually given in electronvolts for the high-energy bands.
The two equations that connect everything
The first ties wavelength and frequency to the speed of light:
c = f × λc is fixed, so frequency and wavelength are inversely proportional
Because c is a constant, when one of f and λ goes up the other must come down. A long wavelength always means a low frequency, and a short wavelength always means a high one. That single relationship explains the whole left-to-right structure of the spectrum.
The second connects frequency to the energy of each photon:
E = h × fh is Planck's constant, 6.626 × 10⁻³⁴ joule seconds
Energy is directly proportional to frequency: higher frequency means a more energetic photon. Combine the two and you get E = hc / λ, which shows energy is inversely proportional to wavelength.
The golden rule of the spectrum: moving from radio waves toward gamma rays, wavelength gets shorter while frequency and energy both rise. Radio waves have the longest wavelengths and the gentlest photons; gamma rays the shortest wavelengths and the most penetrating photons. Everything else falls between, in a smooth and entirely predictable progression.
All Seven Bands
The seven bands of the electromagnetic spectrum
In order from longest wavelength and lowest energy to shortest and highest. The boundaries are approximate, and microwaves formally sit inside the radio band — which is why the two ranges below overlap.
| Band | Wavelength range | Frequency range | Signature use |
|---|---|---|---|
| Radio waves | 1 mm to over 100 km | 3 kHz – 300 GHz | Broadcasting, Wi-Fi, mobile |
| Microwaves | 1 mm to 1 m | 300 MHz – 300 GHz | Radar, 5G, ovens, satellites |
| Infrared | 700 nm to 1 mm | 300 GHz – 430 THz | Thermal imaging, remotes |
| Visible light | 380 to 700 nm | 430 – 790 THz | Human vision, photography |
| Ultraviolet | 10 to 400 nm | 790 THz – 30 PHz | Sterilization, forensics |
| X-rays | 0.01 to 10 nm | 30 PHz – 30 EHz | Medical imaging, security |
| Gamma rays | Below 0.01 nm | Above 30 EHz | Cancer therapy, sterilization |
Band 1 of 7
Radio waves
Radio waves occupy the long-wavelength, low-frequency end of the spectrum, from about a millimetre to well over a hundred kilometres, at frequencies from roughly 3 kHz to 300 GHz. They carry the least energy of any electromagnetic wave, which makes them non-ionizing and harmless to living tissue at everyday intensities.
Their advantage is reach. Radio waves travel long distances and pass through foliage, weather and most building materials, and simple antennas can both emit and receive them. That combination is why they are the backbone of wireless communication.
AM and FM broadcasting, over-the-air television, Wi-Fi, Bluetooth, GPS and mobile phones all live here — phones using the ultra-high-frequency part of the band. Radio astronomy points enormous dishes at the sky to catch the faint natural radio emission of stars, galaxies and gas clouds that ordinary telescopes cannot see at all.
Band 2 of 7
Microwaves
Microwaves are a high-frequency subset of radio, with wavelengths from about a millimetre to a metre. The shortest, under ten millimetres and above 30 GHz, are called millimetre waves. They are still non-ionizing, but they interact with matter in a distinctive and very useful way.
A microwave oven runs at 2.45 GHz — a wavelength of about 12.2 cm. Water molecules absorb that frequency efficiently and rotate rapidly in response, turning electromagnetic energy directly into heat. It is the most everyday demonstration of field energy becoming thermal energy that most people will ever own.
Microwaves also reflect cleanly off solid objects and travel in straight lines, which makes them ideal for radar: aircraft, shipping and storm tracking all depend on it. Satellite links and GPS use microwave bands, and 5G reaches into the millimetre-wave region for very high data rates. The band also carries the oldest light in the universe, covered further down this page.
Band 3 of 7
Infrared radiation
Infrared sits just beyond the red end of visible light, from about 700 nanometres to 1 millimetre. It was the first invisible light ever discovered, and it has a special relationship with temperature: every object with any warmth at all emits infrared, and the hotter it is, the more it emits. Infrared is, in effect, the language of heat.
The band divides into near-infrared (closest to visible light), mid-infrared and far-infrared (closest to microwaves), each with its own behaviour and applications.
Because warm things glow in infrared, thermal cameras can see people, animals and machinery in total darkness. Night vision, building-insulation surveys and medical thermography all work this way. Infrared also carries information: a television remote sends commands as infrared pulses, and fibre-optic networks transmit data as near-infrared light through glass. In astronomy, infrared telescopes such as the James Webb see straight through the dust clouds that block visible light, revealing newborn stars and the earliest galaxies.
Band 4 of 7
Visible light
Visible light is the narrow band the human eye can detect, from roughly 380 nanometres at the violet end to 700 at the red end, at frequencies between about 430 and 790 terahertz. Central as it feels to our experience, it spans only about 0.00032 millimetres of wavelength — an almost invisibly thin slice of the whole spectrum.
Every colour we can see lies inside that sliver, and the colours always appear in the same order because that order is simply wavelength order. Red has the longest wavelength and the lowest photon energy; violet the shortest and the highest. The mnemonic ROYGBIV captures the sequence.
The colours of visible light by wavelength
| Colour | Wavelength range | Relative energy |
|---|---|---|
| Red | 625 to 700 nm | Lowest |
| Orange | 590 to 625 nm | Low |
| Yellow | 565 to 590 nm | Medium-low |
| Green | 500 to 565 nm | Medium |
| Blue | 450 to 485 nm | High |
| Violet | 380 to 450 nm | Highest |
The word "spectrum" itself comes from visible light. Newton used the Latin word for "appearance" in his 1672 paper to the Royal Society, describing the band of colours a prism produces; the full treatment appeared in Opticks in 1704. He listed seven colours, adding indigo specifically so the count would match the seven notes of the musical scale and the seven planets then known. Modern practice generally recognises six, since the eye struggles to separate indigo from blue and violet.
Band 5 of 7
Ultraviolet radiation
Ultraviolet lies just beyond violet, from about 10 to 400 nanometres. Its photons carry more energy than visible light, and it is here that radiation starts to become biologically dangerous. The band splits into UV-A (315–400 nm), UV-B (280–315 nm) and UV-C (200–280 nm), with shorter wavelengths called extreme or vacuum ultraviolet.
The Sun is the main natural source, and the atmosphere is what protects us. UV-C, the most harmful, is absorbed high above the ground and never reaches us. Roughly 95 percent of UV-B is absorbed by the ozone layer; the fraction that gets through causes sunburn and, over time, raises the risk of skin damage. UV-A passes most easily and drives skin ageing.
The same energy that makes UV hazardous also makes it useful. It kills bacteria and viruses, so UV lamps sterilize water, air and medical equipment. Forensic teams use it to reveal fingerprints and bodily fluids, banks use it to check banknotes, and moderate exposure lets the body make vitamin D. Humans cannot see ultraviolet, but bees and many insects can — they read UV patterns on flowers that are completely invisible to us.
Band 6 of 7
X-rays
X-rays run from about 0.01 to 10 nanometres, far shorter than ultraviolet. Their photons carry enough energy to knock electrons out of atoms and break chemical bonds, which makes them ionizing — and gives them their most famous ability: seeing inside solid objects.
X-rays pass easily through soft tissue but are absorbed by denser material like bone and metal. Directed through the body onto a detector, dense structures cast shadows, producing the images used to diagnose fractures, dental problems and chest disease. The same penetrating power inspects luggage at airports and checks welds and castings for hidden flaws.
Because they are ionizing, exposure is controlled carefully: the diagnostic benefit is weighed against the dose, and modern equipment uses the lowest dose that still yields a clear image. Beyond Earth, X-ray astronomy studies the most violent objects known — black holes, neutron stars, and the superheated gas between galaxies. The atmosphere blocks these rays entirely, so X-ray telescopes such as Chandra must work from orbit.
Band 7 of 7
Gamma rays
Gamma rays occupy the extreme end: wavelengths below 0.01 nanometres, smaller than an atom. They carry the highest photon energy, the highest frequency and the greatest penetrating power of any electromagnetic radiation. Strongly ionizing, they pass through most materials and cause serious biological damage — the most hazardous part of the spectrum, and in controlled hands one of the most useful.
They come from the most energetic processes known: radioactive decay, nuclear reactions, and violent astrophysics. On Earth they are produced by decaying radioactive elements and inside reactors. In space they pour out of supernovae, pulsars and the discs of matter spiralling into black holes.
Medicine turns that danger into treatment. In radiotherapy, tightly focused gamma beams destroy tumour cells while sparing surrounding tissue. Gamma radiation also sterilizes medical equipment and some foods, killing bacteria without leaving residue. In nuclear medicine, PET scans use gamma emission to image processes inside the living body. Astronomers study cosmic gamma rays from space-based observatories, since the atmosphere stops them long before they reach the ground.
Safety
Ionizing vs non-ionizing radiation
The most important division in the spectrum. It decides whether a band is safe for everyday exposure or demands careful protection, and it comes down entirely to the energy of the photons.
Non-ionizing radiation covers radio waves, microwaves, infrared, visible light and the lower-energy part of ultraviolet. These photons cannot tear electrons away from atoms. They still have effects — microwaves and infrared heat materials by setting molecules vibrating, and lower ultraviolet breaks some chemical bonds, which is what sunburn is — but they cannot ionize, so they do not damage matter in the deep, cumulative way higher-energy radiation does. Nearly all laser light is non-ionizing too.
Ionizing radiation covers the higher-energy part of ultraviolet along with all X-rays and gamma rays. These photons carry enough energy to knock electrons out of atoms, creating ions and breaking the molecular bonds that hold living tissue together. That is what makes ionizing radiation capable of DNA damage, cell death and cancer, and why it is handled under strict controls.
The boundary is not perfectly sharp, because different atoms ionize at slightly different energies. The transition is generally placed within the ultraviolet band, somewhere between about 10 and 33 electronvolts, with roughly 12 eV often cited as the practical threshold. This is why ultraviolet is the pivotal band: its lower reaches merely cause sunburn, while its upper reaches cross into genuinely cell-damaging territory.
History
How the spectrum was discovered
For most of human history people knew of one kind of light: the kind they could see. The discovery that it was a sliver of something enormous unfolded over roughly a century, each experiment pushing the known boundary further out.
- 1672Isaac Newton splits sunlight with a prism and uses the Latin word spectrum, meaning appearance, for the band of colours it produces. He presents it to the Royal Society; the full argument appears in Opticks in 1704.
- 1800William Herschel puts thermometers in each colour of a prism's spectrum and one just beyond the red edge, where no light falls. It reads hottest of all. He has found infrared — the first proof that light exists outside human vision.
- 1801Johann Wilhelm Ritter looks at the other end, placing silver chloride just beyond violet. It darkens faster there than anywhere in the visible band, revealing ultraviolet. In two years the spectrum has grown invisible extensions at both ends.
- 1865James Clerk Maxwell unifies electricity, magnetism and light in four equations. His derived wave speed matches the measured speed of light, and his theory implies a continuous spectrum of waves at any wavelength — most of it then unknown.
- 1887Heinrich Hertz generates and detects radio waves in the laboratory, showing they reflect, refract and travel at the speed of light exactly as Maxwell predicted. The unit of frequency now carries his name.
- 1895Wilhelm Röntgen notices a screen glowing across the room from a covered cathode ray tube, and names the unknown radiation X-rays. Within a week he images his wife's hand, bones and wedding ring. He receives the first Nobel Prize in Physics in 1901.
- 1900sGamma rays, found through the study of radioactivity, are confirmed as electromagnetic waves of extremely short wavelength, closing the high-energy end of the spectrum.
- 1940sMicrowaves are pinned down as a distinct working band during wartime radar research, filling the last major gap between radio and infrared.
- 1965Arno Penzias and Robert Wilson cannot get rid of a faint hum in their antenna, arriving equally from every direction. It is the cosmic microwave background — the oldest light in the universe.
The Oldest Light
The cosmic microwave background
One of the strangest parts of the spectrum is a faint microwave glow that fills all of space in every direction. It is the oldest light in the universe — a direct remnant of the Big Bang.
It was released about 380,000 years after the Big Bang, the moment the young universe cooled enough for light to travel freely. In the 13.8 billion years since, the expansion of space has stretched that ancient light to longer and longer wavelengths. What began as intense, high-energy radiation has been redshifted all the way down into the microwave band, cooling to just 2.7 kelvin — about −270 °C, a few degrees above absolute zero.
It is also astonishingly abundant. There are roughly 400 of these ancient photons in every cubic centimetre of space, and their combined energy density exceeds that of all the light emitted by every star in the history of the universe.
It was found by accident. In 1965 Arno Penzias and Robert Wilson could not rid their antenna of a faint hum arriving equally from every direction. The hum was the echo of the Big Bang, and it won them the Nobel Prize. Studying it has since become one of cosmology's sharpest tools — a baby photo of the universe, revealing its age, composition and shape.
Atmospheric WindowsGets through Blocked
Why the atmosphere shapes what we can see
The spectrum reaching Earth from space is vast, but our atmosphere lets only certain bands through. Those transparent regions are called atmospheric windows, and they have shaped both the evolution of life and the design of modern astronomy.
Visible light & radio
The two main atmospheric windows. It is almost certainly no coincidence that human eyes evolved to see exactly the band that passes most freely through the air and is emitted most strongly by the Sun.
Infrared, UV, X-ray, gamma
Much of the infrared is absorbed by water vapour, most ultraviolet by the ozone layer, and X-rays and gamma rays are stopped high above the ground. Wonderful for life; inconvenient for astronomers.
To see the wavelengths the atmosphere blocks, telescopes have to get above it. That is the entire reason space observatories exist. Hubble observes visible and ultraviolet light from orbit, the James Webb captures infrared, Chandra detects X-rays, and Fermi watches for gamma rays. Even ground-based radio and millimetre telescopes are built on high, dry mountains to rise above as much water vapour as possible — the Atacama Large Millimeter Array sits 5,000 metres up in the Chilean Andes. Each band offers a different view of the cosmos, so opening every window has transformed what we know about it.
Practice
Worked examples
Frequency from wavelength
A radio station broadcasts at a wavelength of 3 metres. What is its frequency?
f = c / λ = (3 × 10⁸) / 3 = 1 × 10⁸ Hz = 100 MHz — squarely in the FM band.
Wavelength from frequency
A microwave oven operates at 2.45 GHz. What is its wavelength?
λ = c / f = (3 × 10⁸) / (2.45 × 10⁹) ≈ 0.122 m = 12.2 cm.
Energy of a photon
What is the energy of a green-light photon with a frequency of 5.7 × 10¹⁴ Hz?
E = hf = (6.626 × 10⁻³⁴)(5.7 × 10¹⁴) ≈ 3.78 × 10⁻¹⁹ J ≈ 2.36 eV.
Comparing energies across the spectrum
An X-ray photon at 3 × 10¹⁸ Hz against a visible photon at 5 × 10¹⁴ Hz. How much more energy does it carry?
E ∝ f, so about 6,000 times more — which is why one is ionizing and the other is not.
Energy straight from wavelength
Combine the two equations to find the photon energy of 500 nm green light.
E = hc/λ = (6.626 × 10⁻³⁴)(3 × 10⁸) / (5 × 10⁻⁷) ≈ 3.98 × 10⁻¹⁹ J ≈ 2.48 eV.
Where does ionization begin?
Roughly what wavelength corresponds to a 12 eV photon, the practical ionizing threshold?
λ = hc/E ≈ 1240 eV·nm / 12 eV ≈ 103 nm — deep in the ultraviolet, exactly where the boundary sits.
Applications
The spectrum as an industry
The electromagnetic spectrum is not only a scientific concept. It is the invisible foundation of entire global industries.
Medical imaging
X-rays, gamma rays and other bands underpin one of the largest technology markets in healthcare. The global medical imaging market was valued at around $46 billion in 2025 and is projected to reach roughly $81 billion by 2035, growing at close to 6 percent a year. X-ray devices alone accounted for about $14 billion in 2025, with North America holding over a third of the global market.
Communications and broadcasting
Radio and microwave bands carry nearly all wireless communication on the planet: mobile networks, Wi-Fi, satellite links, broadcast radio and television, GPS and 5G. Governments treat spectrum as a national resource and auction slices of it to carriers for sums that routinely run into billions.
Industrial and scientific
Infrared drives thermal imaging, night vision and fibre-optic data. Ultraviolet powers sterilization and semiconductor photolithography. Microwaves cook food and run aviation and weather radar. Gamma rays sterilize medical supplies and treat cancer. Each band has an industry built on it.
FAQ
Electromagnetic spectrum: common questions
What are the 7 types of electromagnetic waves in order?
From longest wavelength to shortest, the seven types are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Moving along that order toward gamma rays, wavelength decreases while frequency and photon energy both increase. All seven travel at the speed of light in a vacuum.
What is the electromagnetic spectrum in simple terms?
It is the complete family of electromagnetic waves, arranged by wavelength and frequency. Every kind of light, from radio waves to gamma rays, belongs to it. They are all the same sort of wave, made of oscillating electric and magnetic fields, and differ only in wavelength and the energy each photon carries. Visible light is the only part humans can see, and it is a very small portion of the whole.
Which electromagnetic wave has the highest energy?
Gamma rays. They have the shortest wavelengths, below 0.01 nanometres, and the highest frequencies, above 30 exahertz. Because photon energy is directly proportional to frequency, gamma-ray photons are the most energetic and most penetrating in the spectrum. Radio waves, at the opposite end, carry the least.
Which electromagnetic wave has the longest wavelength?
Radio waves, ranging from about one millimetre to over one hundred kilometres. Because wavelength and frequency are inversely related, radio waves also have the lowest frequency and the least energy per photon, which is why they are non-ionizing and safe for everyday communication.
Do all electromagnetic waves travel at the same speed?
In a vacuum, yes — all of them travel at exactly 299,792,458 metres per second regardless of band. A radio wave and a gamma ray released together would move through empty space side by side. They differ in wavelength, frequency and energy, not speed. Passing through a medium such as glass or water slows them down, but in a vacuum the speed is always the same.
What is the difference between ionizing and non-ionizing radiation?
Ionizing radiation carries enough energy per photon to knock electrons out of atoms and break chemical bonds, which can damage DNA and cause cancer. It covers high-energy ultraviolet, X-rays and gamma rays. Non-ionizing radiation — radio waves, microwaves, infrared, visible light and low-energy ultraviolet — cannot remove electrons from atoms. The boundary falls inside the ultraviolet band, at a photon energy of roughly 10 to 33 electronvolts.
Why can't we see most of the electromagnetic spectrum?
Human eyes evolved to detect only about 380 to 700 nanometres, because that is the range that passes most freely through Earth's atmosphere and is emitted most strongly by the Sun. Other bands have wavelengths too long or too short for the eye's receptor cells to respond to, so detecting them needs instruments: radios, infrared cameras, X-ray machines and the rest.
Who discovered the electromagnetic spectrum?
No single person. It was mapped over roughly a century. William Herschel found infrared in 1800 and Johann Ritter ultraviolet in 1801. Maxwell unified light as an electromagnetic wave in 1865, Hertz generated radio waves in 1887, and Röntgen discovered X-rays in 1895. Gamma rays followed from the study of radioactivity, and microwaves were pinned down during wartime radar research.
What is the cosmic microwave background?
A faint microwave glow filling all of space in every direction — the oldest light in the universe. It was released about 380,000 years after the Big Bang, when the cooling universe first let light travel freely, and the expansion of space has since stretched it into the microwave band at a temperature of just 2.7 kelvin. Penzias and Wilson found it by accident in 1965 and won a Nobel Prize for it.
What is the electromagnetic spectrum used for?
Every band has practical uses. Radio waves carry broadcasting and mobile communication, microwaves run radar and ovens, infrared enables thermal imaging and fibre optics, visible light lets us see, ultraviolet sterilizes and detects forgery, X-rays produce medical images, and gamma rays treat cancer and sterilize equipment. Together these support industries worth hundreds of billions of dollars.
Summary
Key takeaways
The electromagnetic spectrum is the full range of electromagnetic radiation, from radio waves over 100 kilometres long to gamma rays smaller than an atom. Its seven bands, in order of decreasing wavelength, are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All are the same kind of transverse wave, differing only in wavelength, frequency and energy.
Two equations govern all of it. c = f × λ links wavelength and frequency through the constant speed of light, and E = h × flinks frequency to photon energy. Together they give the fundamental rule that shorter wavelength always means higher frequency and higher energy.
The critical safety division is between non-ionizing radiation — everything from radio waves up to low-energy ultraviolet — and ionizing radiation, meaning high-energy ultraviolet, X-rays and gamma rays. Only the latter can knock electrons out of atoms and damage living tissue.
Mapped over a century by Herschel, Ritter, Maxwell, Hertz and Röntgen, the spectrum now underpins modern life. It carries every wireless signal, produces every medical scan, and lets astronomers read the oldest light in the universe. From the cosmic microwave background echoing the Big Bang to the X-ray that sets a broken bone, it connects the largest questions in science with the most practical tools of everyday life.
Keep Going
Explore further
What Is a Transverse Wave?
Why light is transverse, how polarization proves it, and the anatomy of a wave.
Transverse vs Longitudinal
The two wave families compared, and why only transverse waves polarize.
What Is a Longitudinal Wave?
Sound, compressions and rarefactions — the other half of wave physics.
Wave Calculator
Solve c = fλ and E = hf for any band of the spectrum.
Interactive Simulator
Drag amplitude, frequency and wavelength and watch a wave respond.
Glossary
Every wave term on this site, defined and cross-linked.