Fotonienergia

Fotonienergia refers to the energy carried by a single photon, the quantum of light in quantum theory. It is proportional to the light’s frequency and inversely proportional to its wavelength in vacuum, given by E = hν = hc/λ, where h is Planck’s constant, ν is frequency, λ is wavelength, and c is the speed of light. The energy is commonly expressed in joules or electronvolts (1 eV = 1.602×10^-19 J). A photon has zero rest mass and moves at the speed of light in vacuum, and its momentum is p = E/c = h/λ. The energy per photon is independent of the light’s intensity; increasing brightness increases the photon flux, not the energy per photon.

Photonienergia governs interactions with matter. Photons can be absorbed or emitted when their energy matches electronic transitions or band gaps, leading to phenomena such as the photoelectric effect, fluorescence, and spectroscopy. In solids, the energy scale of photons relates to electronic structure, excitons, and phonons.

In a medium, the frequency ν remains unchanged when light enters or leaves a boundary, while the wavelength becomes λ = λ0/n, with n the refractive index. The momentum of a photon in a medium is subject to interpretation (often discussed in the context of the Abraham–Minkowski controversy) but the energy remains E = hν.

Applications span photovoltaics, lasers, optical communications, and imaging. Typical visible photons have energies from about 1.8 eV (red, ~700 nm) to about 3.1 eV (violet, ~400 nm).