Lightradiation

Lightradiation is a form of electromagnetic radiation that encompasses the portion of the spectrum perceived as light by the human eye, along with adjacent ultraviolet and infrared bands that are still considered part of optical radiation. It consists of photons and exhibits both wave-like and particle-like properties. In vacuum, lightradiation travels at the speed of light, c, and carries energy proportional to its frequency, given by E = hν.

The optical spectrum spans roughly 380 to 750 nanometers for visible light, with shorter wavelengths in the ultraviolet and longer wavelengths in the infrared. The wavelength and frequency of lightradiation determine color, energy per photon, and how it interacts with matter. Lightradiation can be coherent, as in lasers, or incoherent from most lamps, and it may be polarized. Its propagation is affected by the medium, including effects such as refraction, reflection, and dispersion.

Generation of lightradiation occurs through several mechanisms: thermal emission from hot bodies, electroluminescence in diodes, fluorescence and phosphorescence, and chemical or biological luminescence. Coherent sources such as lasers produce light with a narrow spectral width and fixed phase relationship, while broad-spectrum sources emit a wide range of wavelengths.

Interactions with matter include absorption, reflection, transmission, scattering, and diffraction. Absorption can excite electronic transitions or vibrational modes, convert light to heat, or drive photochemical reactions. Measurement of lightradiation uses radiometric and photometric quantities, including radiant flux, radiant intensity, spectral irradiance, and, for human perception, illuminance measured in lux.

Applications span lighting, imaging, communication, astronomy, medicine, and spectroscopy. Safety considerations address potential damage from high-intensity or ultraviolet exposure, directing the use of filters, shields, and exposure limits in relevant environments.