What is Light?
Light is electromagnetic radiation that is visible to the human eye. Illumination of 400–700 nm, between infrared (longer wavelengths) and ultraviolet (shorter wavelengths) (with shorter wavelengths). The term “light” in physics refers to electromagnetic radiation of any wavelength, visible or not. Light includes gamma rays, X-rays, microwaves, and radio waves. Light has four basic properties: intensity, propagation direction, and polarisation. Its speed in a vacuum, 299 792 458 m/s, is a basic constant. Visible light, like all electromagnetic radiation, is propagated by massless constituent particles called photons, which can be examined as both waves and particles. Optics is a major research topic in modern physics. The Sun is Earth’s principal light source. Fire has long been a source of illumination for people, from ancient campfires to modern kerosene lamps. Electric lights and electricity systems have effectively supplanted firelight.