Frequency describes how many oscillations of a light wave pass a given point each second, typically expressed in hertz (Hz). The visible spectrum spans roughly 430 THz (red) to 750 THz (violet), though electromagnetic waves outside this range—such as radio waves below 1 GHz and gamma rays above 3 × 1018 Hz—are invisible to the human eye.
Because a wave is a conduit of energy, higher frequency equates to greater energy per photon. Consequently, gamma rays carry the most energy, while radio waves are the least. Within visible light, violet photons hold the highest energy and red photons the lowest.
Wavelength, the distance between successive peaks or troughs, is inversely proportional to frequency. Shorter wavelengths (e.g., violet) correspond to higher frequencies and greater energy; longer wavelengths (e.g., red) have lower frequencies and less energy.
All electromagnetic waves travel at the same speed in a vacuum—approximately 186,000 miles per second (300,000 km/s)—the universal speed limit. In media such as air, water, or glass, light slows and bends, a phenomenon known as refraction.
These principles underpin technologies ranging from fiber‑optic communications to spectroscopic analysis, illustrating the profound link between a wave’s frequency, wavelength, and energy.
