How to Convert Nanometers to Electronvolts (nm to eV) In physics and chemistry, you often need to convert between light wavelength and photon energy. Wavelength is usually measured in nanometers (nm). Photon energy is often measured in electronvolts (eV).
Because wavelength and energy are inversely related, shorter wavelengths have higher energy. This guide provides the formula, a shortcut, and step-by-step examples to make the conversion simple. The Physics Formula The relationship between energy ( ) and wavelength ( ) is determined by the Planck-Einstein relation:
E=hcλcap E equals the fraction with numerator h c and denominator lambda end-fraction = Energy in Joules (J) = Planck’s constant ( = Speed of light ( = Wavelength in meters (m)
To get the energy directly in electronvolts when the wavelength is in nanometers, we combine the constants (
, and the charge of an electron) into a single conversion factor. The Handy Shortcut Formula
For quick calculations, physicists use a simplified approximation.
E (eV)≈1240λ (nm)cap E (eV) is approximately equal to the fraction with numerator 1240 and denominator lambda (nm) end-fraction
(Note: For highly precise scientific work, the more exact value of 1239.81239.8 is preferred.) Step-by-Step Conversion Examples Example 1: Converting Green Light (550 nm)
Let’s find the energy of a typical green light photon with a wavelength of 550 nm. Take the constant: 1240 Divide by the wavelength: 550 Example 2: Converting Ultraviolet Light (300 nm)
Let’s find the energy of a shorter, higher-energy UV photon. Take the constant: 1240 Divide by the wavelength: 300 Quick Reference Conversion Chart Wavelength (nm) Light Spectrum Energy (eV) Green Light Violet Light Ultraviolet (UV)
If you want to dive deeper into this calculation, let me know if you need to: Calculate the reverse conversion from eV to nm See the full algebraic derivation using SI units Solve a specific homework or laboratory problem
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