Table of Contents
What Is the Frequency of Light?
Light is electromagnetic radiation, and like all waves it has a frequency — the number of wave cycles per second. Visible light spans frequencies from about 430 THz (red) to 770 THz (violet). The frequency of light is directly related to its color and energy. Higher frequency means shorter wavelength, higher energy, and a shift toward violet.
The relationship between frequency and wavelength is governed by the speed of light in vacuum, c = 299,792,458 m/s. This relationship is fundamental to spectroscopy, optics, astronomy, and quantum mechanics. Photon energy is proportional to frequency through Planck's constant.
Formulas
Visible Light Spectrum
| Color | Wavelength (nm) | Frequency (THz) | Energy (eV) |
|---|---|---|---|
| Red | 620-750 | 400-484 | 1.65-2.00 |
| Orange | 590-620 | 484-508 | 2.00-2.10 |
| Yellow | 570-590 | 508-526 | 2.10-2.17 |
| Green | 495-570 | 526-606 | 2.17-2.50 |
| Blue | 450-495 | 606-668 | 2.50-2.75 |
| Violet | 380-450 | 668-789 | 2.75-3.26 |
Frequently Asked Questions
Does light always travel at the same speed?
Light travels at c in vacuum. In other media (glass, water, air), light slows down. The ratio of c to the speed in a medium is the refractive index. When light enters a denser medium, its speed and wavelength decrease but its frequency remains the same.
Why is UV light more dangerous than visible light?
Ultraviolet light has higher frequency and thus higher photon energy than visible light. Each UV photon carries enough energy to break chemical bonds in DNA and other biological molecules, which can lead to cell damage, mutations, and skin cancer with prolonged exposure.
What is a wavenumber?
Wavenumber is the reciprocal of wavelength, typically expressed in cm^-1 in spectroscopy. It represents the number of wave cycles per unit distance and is proportional to frequency and energy, making it convenient for infrared and Raman spectroscopy measurements.