Non-Ionizing Radiation Definition

Non-ionizing radiation is any kind of radiation in the electromagnetic spectrum that does not have enough energy to remove an electron from an atom and turn it into an ion. This contrasts with ionizing radiation like x-rays, gamma rays and alpha particles, which come from the other end of the spectrum and are unstable and reactive. Non-ionizing radiation can generate heat, which is how food is cooked in a microwave oven. Humans and other organisms can see some types of non-ionizing radiation, such as visible light and infrared light.

Non-Ionizing Radiation
The image above shows the types of non-ionizing radiation on the electromagnetic spectrum.

Examples of Non-Ionizing Radiation


Ultraviolet (UV) radiation comes from the sun, welding, black lights and UV lasers. The sun emits UVA, UVB and UVC rays. UVC rays are absorbed by the ozone layer and never actually reach the Earth. Both UVA and UVB light are important for humans in the production of Vitamin D. However, the effects of overexposure to UV rays can be negative and can be immediate or delayed. Sunburn, skin cancer and cataracts develop over time with excessive exposure.

Visible Light

The visible light portion of the electromagnetic spectrum can be seen by humans, animals and other organisms. This type of light consists of seven colors: red, orange, yellow, green, blue, indigo and violet. When all the colors are present at one time, the light is white. Rainbows are created when visible light passes through raindrops. The raindrops act like a prism and break the light down into its individual colors. Overexposure to visible light can damage both the eyes and skin.


Everything on Earth gives off some amount of infrared (IR) radiation. The human eye can’t see most of the IR spectrum, but we can feel it as heat. IR radiation is used in furnaces, heat lamps, toasters, night-vision goggles and the lasers seen on TV remote controls. About half of the total energy the sun gives off is in the form of IR radiation, which we feel as heat. In large amounts, this type of radiation can damage the eyes and even cause blindness.

IR radiation from the sun is normally absorbed by the Earth’s surface and the clouds, then released as heat into the atmosphere. When the atmosphere has a lot of water vapor, along with nitrogen, sulfur and fluorocarbons, the IR radiation gets trapped and causes the atmospheric temperature to rise. This is called the greenhouse effect. Temperature increases like this cause changes in the weather patterns on Earth and lead to climate change.


Microwave radiation (MW) comes from microwave ovens, radar, transmission towers, satellite transmissions, the sun and Cosmic Microwave Background (CMB) radiation. CMB is radiation left over from the Big Bang when the universe began. A microwave oven works because microwaves excite the water molecules in food and cause them to vibrate, generating heat and cooking the food. Atoms and molecules can also emit and absorb MW radiation. Overexposure to MW radiation can cause cataracts and skin burns.

There are three subcategories of MW radiation. Extremely high frequency (EHF) waves are used in remote sensors and radio astronomy. Super high frequency (SHF) waves are commonly used in microwave ovens, radar transmitters, cell phones and satellite communications. Finally, the ultra-high frequency (UHF) is used in television broadcasts, walkie-talkies and cordless phones. Microwaves are sometimes grouped with radio waves because these two types of non-ionizing radiation have some overlap on the electromagnetic spectrum.

Radio Frequencies

AM and FM radio broadcasts, Wi-Fi signals, cell phones, amateur radio, television and airport security scanners use radio frequency (RF) waves. This type of non-ionizing radiation is absorbed throughout the body. The effects of RF waves on the body are similar to MW radiation in terms of heat generation. For example, using a cell phone causes the ear and/or head to get warm. Like MW radiation, RF waves are divided into categories: high frequency (HF), medium frequency (MF), low frequency (LF) and very low frequency (VLF). There is no scientific proof that RF non-ionizing radiation increases the risk of cancer or causes any harmful effects on the body.

Extremely Low Frequencies

Extremely low frequency (ELF) waves are on the far end of the electromagnetic spectrum and come from power lines, electrical equipment and wiring, and electrical appliances such as electric blankets, refrigerators, razors and hair dryers. ELF waves can go through water so they are also used for detection by submarines. According to the National Cancer Institute, there is no experimental evidence showing that normal levels of ELF radiation are dangerous to humans.


Lasers aren’t a form of non-ionizing radiation, but they are made from it. The word laser is an acronym for Light Amplification by the Stimulated Emission of Radiation. Lasers stimulate atoms and molecules and cause them to produce light and concentrate it into a beam of radiation. Lasers can be made from visible light, UV and IR waves. Store checkout scanners, CD and DVD players, remote controls, dental drills, laser pointers and laser printers all use lasers. They have many industrial and medical applications as well. Masers work in the same way, except they amplify MW and RF waves (the “M” stands for microwave). Lasers are also made from the elements argon, helium and neon, ruby crystals, chemicals and liquid dyes. When not used properly, lasers burn and cause severe damage to tissues, especially in the eye. The narrow beam of light concentrates the effects on the retina, causing blind spots.


1. Which of the following is NOT an example of non-ionizing radiation?
A. Ultraviolet
B. X-ray
C. Microwave
D. Visible light

Answer to Question #1
B is correct. X-rays are an example of ionizing radiation.

2. How do microwave ovens work?
A. They use lasers to heat the food.
B. They spin the food really fast which makes it heat up.
C. They excite the water molecules in food and cause them to vibrate, generating heat.
D. They use the sun to heat food, and you can go blind if you stare at one.

Answer to Question #2
C is correct. The microwaves in a microwave oven excite the water molecules in food. This makes the molecules vibrate, which generates heat and cooks the food.

3. Exposure to normal levels of extremely low frequency (ELF) waves causes ______________.
A. brain damage
B. asthma
C. severe burns
D. no damaging effects

Answer to Question #3
D is correct. Exposure to normal levels of extremely low frequency (ELF) waves causes no damaging effects.


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