Photon energy calculator
This photon energy calculator turns wavelength or frequency into energy. A 500 nm photon (green light) carries E = 3.97289 × 10⁻¹⁹ J, which is 2.47968 eV.
Example: What is given: Wavelength · Wavelength λ 500 nm → Result: E = 3.97289 × 10⁻¹⁹ J = 2.47968 eV. Source: NIST CODATA 2022: Planck constant h = 6.62607015 × 10⁻³⁴ J s, speed of light c = 299 792 458 m/s, elementary charge e = 1.602176634 × 10⁻¹⁹ C (exact values). Updated: .
How it is calculated
A photon is a quantum of light whose energy depends only on its frequency. Short-wavelength light – blue, ultraviolet, X-rays – carries more energy per photon than long-wavelength light such as red or infrared.
Formulas
E = h·f = h·c / λ with the Planck constant h = 6.62607015 × 10⁻³⁴ J·s and the speed of light c = 299,792,458 m/s. To convert to electronvolts, 1 eV = 1.602176634 × 10⁻¹⁹ J. The photon’s momentum is p = h / λ.
Worked example
Green light with λ = 500 nm: E = h·c / λ = 3.97289 × 10⁻¹⁹ J = 2.47968 eV, the frequency is 599.585 THz and the momentum 1.32521 × 10⁻²⁷ kg·m/s. Given f = 600 THz, E = 3.97564 × 10⁻¹⁹ J = 2.4814 eV and λ = 499.654 nm. A photon with exactly 1 eV has λ = 1,239.84 nm, in the near infrared.
- Rule of thumb: λ in nm = 1239.84 / E in eV.
- Visible light corresponds to roughly 1.65 to 3.26 eV.
- The wavelength is the vacuum value; in glass or water λ changes, but the photon energy does not.
Frequently asked questions
How do I calculate photon energy from wavelength?
Use E = h·c / λ. At 500 nm this gives 3.97289 × 10⁻¹⁹ J or 2.47968 eV.
How do I convert joules to electronvolts?
Divide by 1.602176634 × 10⁻¹⁹ J. 3.97289 × 10⁻¹⁹ J becomes 2.47968 eV.
Why does blue light have more energy than red?
Its frequency is higher and its wavelength shorter, and E is proportional to frequency. At 450 nm it is about 2.76 eV, at 700 nm only about 1.77 eV.
Sources and legal basis
- NIST CODATA 2022: Planck constant h = 6.62607015 × 10⁻³⁴ J s, speed of light c = 299 792 458 m/s, elementary charge e = 1.602176634 × 10⁻¹⁹ C (exact values)
- Wikipedia – Photon energy
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