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What is a photon? Definition, energy, types, properties and use

What is a photon? Definition, energy, types, properties and use

Photons are elementary particles that play a fundamental role in the world of physics and nature itself. These particles, often called "light particles," have surprising properties and play a crucial role in various phenomena, from visible light to power generation in solar panels.

In this article, we will explain what photons consist of, their characteristics, their importance in physics and their applications in our daily lives.

What are photons?

Photons are subatomic particles that belong to the boson family. A photon is defined as a quantum of energy in the form of electromagnetic radiation, emitted or absorbed by matter.

What is a photon? Definition, energy, types, properties and useUnlike electrons and protons, which have mass, photons are massless particles at rest, meaning they travel at the speed of light in a vacuum (approximately 299,792,458 meters per second).

This property makes them unique in the realm of subatomic particles. Although photons are commonly associated with visible light, they actually span the entire electromagnetic spectrum. These types of radiation include x-rays, gamma rays, visible light photons, infrared light, radio waves, and microwaves.

Photons are emitted in many natural processes, such as:

  • When a charge accelerates, it emits synchrotron radiation.

  • During a molecular, atomic or nuclear transition to a lower energy level, photons of various energies will be emitted, ranging from radio waves to gamma rays.

  • When a particle and its corresponding antiparticle annihilate.

Properties and characteristics

Energy and frequency

Photon energy corresponds to the energy carried by a single photon. This energy depends on the frequency. Consequently, the energy increases with increasing frequency and wavelength of the photon according to the Planck-Einstein equation:



  • E is the energy of the photon.

  • h is Planck's constant, a fundamental constant of physics.

  • f is the frequency of the photon.

This equation shows that light photons with higher frequencies have more energy than those with lower frequencies. This is evident in visible light, where red photons have less energy than blue photons.

The most used units to indicate the energy of these particles are the electronvolt (eV) and the joule (J). One joule is equivalent to 6.24 × 1018 eV. 

Wave-particle duality

Photons also exhibit a property of wave-particle duality . This means that in certain experiments, photons behave like discrete particles when they interact with matter to transfer a fixed amount of energy, while in others, they behave like electromagnetic waves in phenomena such as refraction.

This duality is a fundamental characteristic of quantum mechanics and manifests itself in phenomena such as interference and diffraction of light.

Zero electrical charge

Photons have no electrical charge. Unlike electrons and protons, which are charge carriers, photons are neutral in terms of electrical charge. This property is essential in electromagnetic interaction and in the transmission of energy through electric and magnetic fields.

Types of photons

All photons are essentially identical in terms of their fundamental properties.

However, based on their energy or frequency, photons can be classified into different types depending on the context in which they are used. Here are some common types of photons:

  1. Visible light photons: These are the photons that make up the light that we can see with our eyes.

  2. Radiofrequency photons: They have a lower frequency than visible light and are used in communication technology, such as radio and television signals.

  3. Microwave photons: Their frequency is even lower and they are used in applications such as microwave ovens and satellite communication.

  4. Infrared photons: Used in thermal imaging technology and wireless communication.

  5. Ultraviolet photons: They have a higher frequency than visible light and are used in applications such as water and surface sterilization.

  6. X-ray photons: They have even higher energy and are used in medicine for imaging and in quality control applications in industry.

  7. Gamma ray photons: they are the ones with the highest energy and frequency in the electromagnetic spectrum. They are used in medicine for radiotherapy and in nuclear research.

Applications in science and everyday life

What is a photon? Definition, energy, types, properties and usePhotons play a fundamental role in physics, especially in quantum theory. Some of the highlights of its importance include:

  • Description of light : They are the carriers of electromagnetic radiation, which means they are responsible for transporting light. The quantum theory of light describes how photons interact with matter.
  • Quantum Electrodynamics (QED) – Quantum Electrodynamics is a theory that describes the interaction between photons and charged particles, such as electrons and positrons.
  • Technology : These particles play a crucial role in technologies such as fiber optics, satellite communication, nuclear magnetic resonance (NMR).
  • Photovoltaic solar energy : In the generation of electricity through the photovoltaic effect of solar panels, the energy of these particles triggers the movement of electrons. 
  • Nuclear Magnetic Resonance (NMR) : NMR uses photons in the radiofrequency range to study the structure and composition of molecules in the human body. It is a fundamental tool in medicine for obtaining precise images of the inside of the body and for scientific research in chemistry and biology.
  • Electronics and communication : Modern electronic devices, such as lasers, LEDs (light-emitting diodes), and photodetectors, depend on the manipulation of photons to function.

History and discovery

What is a photon? Definition, energy, types, properties and useUntil the 17th and 18th centuries, in most prevailing theories, light was considered to be composed of particles. However, as phenomena emerged that particle models could not explain, some scientists proposed wave theories for light.

The modern concept of the photon began to develop gradually in the early 20th century, primarily through the works of Albert Einstein. This concept emerged as a response to experimental observations that challenged the classical model of light as an electromagnetic wave.

Finally, in 1926, optical physicist Frithiof Wolfers and chemist Gilbert N. Lewis introduced the term "photon" to describe these particles, marking an important milestone in understanding the nature of light.

Publication Date: May 13, 2015
Last Revision: October 11, 2023