Electromagnetic Radiation Explained
A foundational concept of nearly everything that we often misunderstand
Electromagnetic radiation (EMR) is everywhere, and it may be one of the most misunderstood yet common aspects of the natural world and science. It’s the light that helps us see, the heat that keeps us warm, and the signal that lets you stream your favorite shows. EMR is ubiquitous, yet so fundamental to our daily lives, science and technology, as well as a guidepost for some of the most profound questions about the universe. This article will give a basic overview of what EMR is and dispel common myths around it, without frying your brain. (sorry, bad joke)
What Is Electromagnetic Radiation?
Electromagnetic radiation (EMR) is energy that travels through space as oscillating electric and magnetic fields. It is one of the fundamental ways that energy is transferred. It can travel through some mediums but can also travel through empty space.
EMR can carry energy and information, making it useful for a wide variety of technologies. Without EMR, there would be no phones, internet, or garage door openers—and we could not see, we would freeze, and the universe could not support life. "Electromagnetic radiation" is synonymous with "light" in physics. Visible light is the narrow band of wavelengths that human eyes have evolved to detect.
Electromagnetic radiation travels as waves at the speed of light in a vacuum—about 300,000 kilometers per second. The distance between peaks of these waves is called wavelength, while the number of peaks passing a point per second is called frequency. All EMR can be categorized based on its wavelength or frequency. Frequency is inversely proportional to wavelength. The electromagnetic spectrum categorizes EMR and determines what we call it based on its wavelength.
Radio Waves:
Wavelength: >1 meter (up to kilometers)
Frequency: <300 MHz (megahertz)
Energy: <2 x 10^-25 J (joules)
Type: Non-ionizing; used for communication (radio, TV, Wi-Fi)
Microwaves:
Wavelength: 1 meter to 1 millimeter
Frequency: 300 MHz to 300 GHz (gigahertz)
Energy: 2 x 10^-25 J to 2 x 10^-22 J
Type: Non-ionizing; used for cooking, radar, and satellite transmissions
Infrared (IR):
Wavelength: 100 µm to 1 µm (micrometers)
Frequency: 3 THz to 300 THz (terahertz)
Energy: 2 x 10^-21 J to 2 x 10^-19 J
Type: Non-ionizing; emitted as heat, used in remote controls and thermal imaging
Visible Light:
Wavelength: 700 nm to 400 nm (nanometers)
Frequency: 430 THz to 750 THz
Energy: 2.6 x 10^-19 J to 5.2 x 10^-19 J
Type: Non-ionizing; the light humans can see, used for vision and optical technologies
Ultraviolet (UV):
Wavelength: 380 nm to 100 nm (nanometers)
Frequency: 790 THz to 3 PHz (petahertz)
Energy: 5.2 x 10^-19 J to 1.6 x 10^-18 J
Type: Ionizing; can cause sunburn and DNA damage but is used for sterilization
X-rays:
Wavelength: 10 nm to 100 pm (picometers)
Frequency: 30 PHz to 3 EHz (exahertz)
Energy: 2 x 10^-17 J to 2 x 10^-15 J
Type: Ionizing; used in medical imaging and airport security
Gamma Rays:
Wavelength: <10 pm (picometers)
Frequency: >30 EHz
Energy: 2 x 10^-14 J
Type: Ionizing; extremely energetic, used in cancer treatment and astronomical observations
Is Electromagnetic Radiation Dangerous?
The answer depends on whether the radiation is ionizing or non-ionizing.
Non-ionizing radiation (radio, microwaves, infrared, visible light) is usually harmless. The only exception where non-ionizing radiation could potentially pose a health risk is if you expose yourself to extremely high power densities, such as standing too close to a radio or microwave transmission tower or heat source. For example, if you stand too close to a hot fire, the infrared radiation will burn you, but if you back up, it's completely harmless.
Ionizing radiation (ultraviolet, X-rays, gamma rays) is the troublemaker. It has enough energy to knock electrons off atoms, turning them into ions. This can damage DNA, which can lead to cancer. The higher the frequency of the wave/photon, the higher its energy and the more damaging it is. While UV radiation is mostly absorbed by the skin (which can cause skin cancer), X-rays and gamma rays penetrate much deeper into the body. Gamma rays’ extreme energy and penetration allow them to create extensive ionization trails, damaging many molecules and cellular structures, including DNA, proteins, and lipids, which can lead to mutations, cell death, or cancer.
The sun emits harmful ionizing radiation in the form of ultraviolet radiation, which the ozone layer helps to partially block, but some still make it to the ground. X-rays are mostly used for medical imaging and airport security, so it's easy to know when you are exposed. Occasional small doses are generally not a problem, but people working with X-rays every day should take precautions. Gamma rays are produced during nuclear reactions and from the radioactive decay of radioactive isotopes. This is what you really want to stay away from, and is what Marie Curie famously discovered—and died from.
It's worth noting that you can't see or feel this radiation, and the only way to determine its presence is with a nuclear radiation detector device such as a dosimeter or Geiger counter. Nearly everything has some natural radioactivity, so there is natural background radioactivity. The worldwide average natural background radioactivity that a person is exposed to is 2.4 (mSv) millisieverts per year, or 0.274 (µSv/hr) microsieverts per hour. This comes from cosmic radiation, terrestrial radioactivity, and even radioactivity in food.
Ionizing electromagnetic radiation is very dangerous, but non-ionizing EMR is not because of the energy per photon (wave). For example, a gamma ray photon has about 50,000 times more energy than a photon of visible light (12.4 keV vs 2.5 eV). However, a microwave photon from a microwave oven has about 250,000 times less energy than a photon of visible light (2.5 eV vs 10.2 meV).
Common Radiation Myths
Electromagnetic radiation is surrounded by misconceptions, often rooted in misunderstanding of how it works. Here are 5 common myths:
“All radiation is dangerous.” People hear "radiation" and think of nuclear disasters, but most electromagnetic radiation is harmless. Non-ionizing radiation, like radio waves and microwaves, lacks the energy to damage cells. Only ionizing radiation is dangerous (UV, X-rays, and gamma rays.)
“Microwaves cause cancer.” As explained earlier, microwaves are non-ionizing and lack the energy to damage DNA. They can heat food because they vibrate water molecules at a specific frequency, not because they're high energy.
“5G is harmful.” Conspiracy theories claim 5G damages health, but 5G radio waves and microwaves are still non-ionizing, just like 4G and Wi-Fi. 5G operates on frequencies from less than 1 GHz to 40 GHz, and even the most energetic photons still have 15,000 times less energy than the light you're using to read this right now. Despite trying, studies have never shown health risks at the levels used by 5G technology.
“Cell phones emit dangerous radiation.” Cell phones emit radio and microwave frequencies, which are non-ionizing and at much lower power levels than harmful forms of EMR.
“Humans can’t emit radiation.” Actually, you’re a walking heat lamp! Your body constantly radiates infrared energy, which is why thermal cameras can see you in the dark. The infrared radiation your body emits is over 1,000 times more energetic than 5G and cell phones!
Understanding the spectrum and its properties clears up these misconceptions.
Wave-Particle Duality
Here’s where electromagnetic radiation gets weird and philosophical. It's both a wave and a particle. The dual nature of EMR was first revealed by experiments like the double-slit experiment, which showed that light behaves as a wave when you’re not looking and as a particle (photon) when you are.
Photons are tiny packets of energy, and the energy of each photon depends on its frequency. Higher frequency means more energetic photons. This wave-particle duality isn’t just a curiosity, it’s a fundamental principle of quantum mechanics.
All Objects Emit Radiation: Blackbody and Grey Body Radiation
Every object in the universe radiates electromagnetic energy—rocks, countertops, pillows, cats, tapioca pudding, and even you—are constantly emitting radiation. Yes, you’re a glowing beacon of infrared light, though you’d need a thermal camera to see it. This phenomenon is called blackbody radiation—the emission of radiation by an object based solely on its temperature. A perfect blackbody absorbs all radiation and emits a predictable spectrum depending on its temperature.
Planck's law says the wavelength of radiation that everything gives off is dependent on its temperature.
λpeak = b/T
where:
λpeak is the peak wavelength (in meters),
T is the object’s temperature in kelvin (K),
b is Wien’s displacement constant (2.897×10^−3 m).
This radiation becomes visible to the human eye when an object is around 525°C (977°F, or ~800 K). At this temperature, the peak of the object's emission shifts into the deep red part of the visible spectrum, making the glow faint but discernible. This is because human eyes are most sensitive to light in the visible spectrum (400–700 nm), but we can begin detecting dim red light at longer wavelengths. As the temperature rises to around 800°C (1472°F, ~1073 K), the glow intensifies and appears orange-red. At 1000°C (1832°F, ~1273 K), the object appears yellow-white as more of the emission shifts into shorter visible wavelengths. Objects below ~525°C radiate primarily in the infrared range, invisible to the naked eye but detectable with infrared cameras.
On this subject, if you've ever wondered why light bulbs are rated based on color temperature, it's because of blackbody radiation. Color temperature is based on the light emitted by an ideal blackbody radiator as it is heated to different temperatures. It represents the temperature in Kelvin (K) at which a blackbody would emit light of a similar hue, making it a standard way to describe the visual warmth or coolness of light sources.
But nothing in the real world is perfect. Real objects are grey bodies, which means they emit less radiation than a perfect blackbody. Still, the principle holds: hotter objects emit photos at shorter wavelengths.
Things around room temperature emit radiation in the infrared spectrum. Each object emits its infrared radiation to other objects around it and simultaneously receives infrared radiation from its surroundings. The net amount of radiation flowing to or from an object can be described by the Stefan-Boltzmann law:
Q = σ ⋅ ε ⋅ A ⋅ (Tobject^4 − Tsurroundings^4)
Where:
Q is the heat energy radiated per unit time (watts),
σ is the Stefan-Boltzmann constant (5.67×10−8 W/m2K4)
ε is the emissivity of the material (0 to 1),
A is the surface area (square meters),
T is the temperature in kelvin.
Photon Energy vs Power Transmission
The energy of a single EM wave or photon depends solely on its frequency, following the formula 𝐸 = ℎ𝜈, where 𝐸 is energy, ℎ is Planck’s constant, and 𝜈 (nu) is the frequency. Higher frequency waves, like X-rays or gamma rays, have more energy per photon than lower frequency waves, like radio or microwaves. Then why do low-energy microwaves heat food so quickly, and flashlight beams do not if visible light photons have more energy than microwave photons?
The power carried by EM waves depends on the total number of photons or waves passing through a point per second. Even low-energy waves, like radio waves, can deliver significant power if there are enough of them. Power is a cumulative measure: more waves or photons means more total energy transferred, regardless of individual energy.
Microwave ovens work by generating electromagnetic waves at 2.45 GHz (12.2 cm wavelength) from a magnetron that vibrate water molecules in food, creating heat through friction. Water molecules have a positive end (hydrogen atoms) and a negative end (oxygen atom), making them "polar" and allowing them to interact with the electric field of microwaves. When exposed to microwaves with just the right wavelength, the water molecules (and other dipole molecules) try to align themselves with the changing electric field, causing them to rotate rapidly back and forth.
Despite popular fears, microwaves are not dangerous to humans because they use non-ionizing radiation—their energy is too low to break molecular bonds or damage DNA. The oven's design also ensures the waves are contained, with safety features like shielding and interlocks to prevent exposure. So, no, standing next to your microwave won’t turn you into a glowing mutant.
Fun Facts
Polarization: EM waves can be polarized, meaning their electric fields oscillate in a specific direction. This is how polarized sunglasses work, blocking certain orientations of light to reduce glare.
Cosmic Microwave Background: The universe itself is glowing with faint microwaves, relics from the Big Bang. The cosmic microwave background tells us a lot about the universe, such as its expansion rate.
Animal Perception: While humans can only see in the visible light range, bees can see ultraviolet, and snakes can see infrared radiation.
Electromagnetic radiation is one of the most important and foundational topics in understanding how things work. It’s a unifying thread that weaves through physics, chemistry, biology, and everyday life. It’s the reason we can talk to people on the other side of the planet, detect galaxies billions of light-years away, and cook popcorn in under three minutes.
So the next time you read an email, open your garage door, or feel the warmth of the sun, remember you’re part of an electromagnetic symphony. And if you ever feel radiant or glowing, you are—in infrared.
Questions for you:
What surprised you most about electromagnetic radiation?
What makes EMR dangerous, and why is 5G safe?
What will you think about differently now that you know what EMR is?
Thank you Tanner. What about radon and radiation that comes from the earth that has been deemed dangerous at certain levels. Is that a myth or no?
I guess the "ionizing" "non-ionizing" distinction depends a least a bit on whihc atom the electon is or is not knocked away from, right?