Light is electromagnetic radiation that travels in waves or particles (photons) and can propagate through a vacuum as well as transparent and translucent media.

  • Here at, we use the term light to refer to the form of electromagnetic radiation that can be perceived by the human eye.
  • Light can be described in terms of:
  • The electromagnetic wave theory of light is a key component of our understanding of light and its interactions with matter. It helps to explain phenomena such as reflection, refraction, and diffraction of light and plays a crucial role in technologies such as wireless communication, remote sensing and medical imaging.
  • In the field of quantum mechanics, light is described as a stream of particles called photons, which are the quanta of the electromagnetic field. According to this theory, photons are elementary particles that carry energy and momentum, and they interact with matter through the electromagnetic force.
  • One of the most famous experiments that demonstrate the particle-like nature of light is the photoelectric effect, in which electrons are emitted from a metal surface when exposed to light. The photoelectric effect can not be explained by the wave theory of light but is explained by Einstein’s theory of the photoelectric effect, which proposes that photons transfer their energy to electrons in the metal.
About light, electromagnetic energy, electromagnetic radiation and radiant energy

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.

Light is electromagnetic radiation (radiant energy), which, detached from its source, is transported by electromagnetic waves (or their quanta, photons) and propagates through space. Even if humans had never evolved, electromagnetic radiation would have been emitted by stars since the formation of the first galaxies over 13 billion years ago.

  • Simply stated, light is energy. Light is the way energy travels through space.
  • Whilst the term light can be used to refer to the whole of the electromagnetic spectrum, visible light refers to the small range of wavelengths that our eyes are tuned to.
  • The term light can be used in three different ways:
  • Light can be used to mean the whole of the electromagnetic spectrum from radio waves, through visible light to gamma rays. When this meaning is intended, the terms radiant energy or photon energy are placed in brackets after the term light in this resource.
  • Light can be used to mean the range of wavelengths and frequencies that can be detected by the human eye. A better term is visible light which refers to the wavelengths that correspond with the colours between red and violet, the visible spectrum.
  • Light can also be used to mean the range of wavelengths and frequencies between infra-red and ultra-violet. This usage is sometimes useful because the outer limits of the visible spectrum can differ under different lighting conditions and for different individuals.
  • Remember that the precise experience of visible light is not exactly the same for all individual humans and is not the same for all living things.
  • Light travels through a vacuum at 299,792,458 metres per second but propagates more slowly through other media.
  • When light interacts with matter it results in optical phenomena such as absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission.