Fény

Fény, in its physical sense, is electromagnetic radiation that is visible to the human eye. It travels as both waves and particles—photons—with energy proportional to frequency (E = hf) and momentum p = h/λ. In vacuum, light moves at about 299,792 kilometers per second. Light can be produced by thermal emission, luminescence, or stimulated emission, and it can propagate through vacuum or materials.

The visible spectrum spans roughly 380 to 750 nanometers; colors are determined by wavelength, while perceived color also depends on the response of photoreceptor cells in the eye. White light is a mixture of wavelengths and can be dispersed into its component colors by refraction. Light interacts with matter through reflection, transmission, absorption, and scattering; the change in direction at interfaces is described by Snell's law, and polarization describes the orientation of the light's electric field.

Historically, the nature of light has been debated, with early theories emphasizing waves or particles. Ibn al-Haytham contributed to optics in the 11th century, Newton advocated a corpuscular view, and later Young and Fresnel supported wave theory. James Clerk Maxwell unified light as an electromagnetic wave, and measurements by Fizeau and Foucault refined its speed.

Applications of light include vision, photography, imaging, fiber-optic communication, lasers, and illumination. The study of light continues to influence physics and technology, from fundamental optics to modern photonics.