What Is Light? The Physics of Waves and Particles

Light is both a wave and a particle, a mystery captured in the concept of wave–particle duality.
As a wave, light travels as oscillating electric and magnetic fields, forming electromagnetic radiation.
Visible light is just one slice of the electromagnetic spectrum, sitting between infrared and ultraviolet.
The speed of light in a vacuum—299,792 kilometers per second—is the ultimate cosmic speed limit.
When treated as particles, light is made of photons, each carrying a tiny packet of energy.
The color of light depends on its wavelength: shorter wavelengths appear blue, longer ones appear red.
Light bends when it changes mediums, a phenomenon called refraction, behind the magic of lenses and rainbows.
Quantum physics shows photons can interfere like waves yet arrive at detectors one by one like particles.
Einstein explained the photoelectric effect by showing photons can knock electrons loose from atoms.
Light not only lets us see but also carries energy, momentum, and even exerts pressure on objects.