Radiant energy

Electromagnetic (EM) radiation can be thought of as:
- Electromagnetic waves, carrying radiant energy in its oscillating electric and magnetic fields.
- Stream of photons, in which case radiant energy can be viewed as photon energy – the energy carried by these photons.
- These two views are completely equivalent and are reconciled to one another in quantum field theory (see wave-particle duality).
Radiant energy includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.
The quantity of radiant energy is measured in terms of radiant flux over time.

Electromagnetic radiation and the electromagnetic energy it transports can be described in terms of waves.
- Electromagnetic radiation (radiant energy) includes all wavelengths of light from radio waves to gamma rays.
Electromagnetic radiation can be described in terms of photons and their properties.
- Energy: Photons have energy that depends on their frequency or wavelength. Higher-frequency photons have more energy than lower-frequency photons.
- Number: The number of photons in a given electromagnetic radiation depends on its intensity or brightness. Higher-intensity radiation has more photons than lower-intensity radiation.
- Direction: Photons travel in straight lines, but their direction can be changed by interacting with matter.
- Polarization: Photons can be polarized, which means that their electric and magnetic fields oscillate in a particular direction.
- Speed: Photons travel at the speed of light, which is approximately 299,792,458 meters per second in a vacuum.

There is a difference in meaning between the terms light, electromagnetic radiation, radiant energy and electromagnetic energy in physics.

- Light is best used to refer to the subset of electromagnetic radiation that is visible to the human eye, ranging from violet (shorter wavelengths) to red (longer wavelengths).

- Electromagnetic radiation refers to the transfer of all forms of electromagnetic radiation through space by electromagnetic waves and includes gamma rays, ultraviolet (UV), infrared (IR), X-rays, and radio waves, as well as visible light.

- Radiant energy is most commonly used to refer to electromagnetic radiation carried by electromagnetic waves. Radiant energy can be measured using instruments such as photometers, which detect the intensity of light or other forms of electromagnetic radiation.

Electromagnetic energy is a more general term that refers to any form of energy that is carried by electromagnetic waves, including both radiant energy and other types of energy that are not radiant (e.g., static electric fields).

The type of energy associated with electromagnetic radiation is a measurable quantity in physics, and its measurement is essential for understanding and analyzing physical systems and processes.
The unit of measurement for electromagnetic energy in the International System of Units (SI) is the joule (J), which is defined as the amount of energy required to perform one joule of work
The electronvolt (eV) is another unit of energy commonly used in atomic and subatomic physics.