Light, often known as visible light, is electromagnetic radiation that falls within the part of the electromagnetic spectrum that the human eye can see. Between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths), visible light is described as having wavelengths in the range of 400″700 nanometres (nm) (with shorter wavelengths). This wavelength corresponds to a frequency range between 430 and 750 terahertz (THz).

Intensity, propagation-direction, frequency or wavelength spectrum, and polarisation are the fundamental characteristics of visible light. Light’s speed in a vacuum, 299 792 458 meters per second (m/s), is one of nature’s fundamental constants. Like all kinds of electromagnetic radiation (EMR), light is observed to constantly move at this speed in a vacuum under experimental circumstances.

The term ‘light’ is occasionally used in physics to refer to electromagnetic radiation of any wavelength, visible or not. Gamma rays, X-rays, microwaves, and radio waves are all light in this sense. Visible light, like all other forms of electromagnetic energy, travels in waves. The energy given by the waves, on the other hand, is absorbed in single places, similar to how particles are absorbed. A photon is the absorbed energy of electromagnetic waves and represents the quanta of light. When a wave of light is converted and absorbed as a photon, the wave’s energy collapses to a single place, and the photon “arrives” at this position. This is referred to as wave function collapse. The wave-particle duality refers to light’s dual existence as a wave and a particle. Optics, or the study of light, is an important research topic in modern physics.

The Sun is the primary source of light on Earth. Fire has always been a significant source of illumination for people, from ancient campfires to modern kerosene lamps. Electric lighting has successfully supplanted firelight as a result of the development of electric lights and power networks.

Radio waves, microwaves, infrared, the visible spectrum that humans see as light, ultraviolet, X-rays, and gamma rays are all types of EM radiation (the term “radiation” excludes static electric, magnetic, and near-field forces).

EMR’s behavior is determined by its wavelength. Wavelengths are shorter at higher frequencies and longer at lower frequencies. When EMR interacts with single atoms and molecules, the amount of energy per quantum it contains determines how it behaves.

In the visible light area, EMR consists of quanta (called photons) that are at the lower end of the energies that can cause electronic excitation within molecules, resulting in changes in the molecule’s bonding or chemistry. Because its photons no longer have enough individual energy to cause a lasting molecular change (a change in conformation) in the visual molecule retinal in the human retina, EMR becomes invisible to humans (infrared) at the lower end of the visible light spectrum. This change triggers the sensation of vision.

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