Case 1
- Wavelength
- 5e-7m
2.479684eV
Open with these valuesPhoton Energy Calculator
2.479684eV
Result: 2.479684 eVA photon carries E = h × c ÷ λ, which in electronvolts is 1.239841984 divided by the wavelength in micrometres. Green light at 500 nm is 2.48 eV, red at 700 nm only 1.77 eV. Enter the wavelength in metres: 500 nm is 0.0000005.
Worked examples
Case 2
- Wavelength
- 7e-7m
1.771203eV
Open with these valuesCase 3
- Wavelength
- 1e-9m
1,239.841984eV
Open with these valuesHow it's calculated
E = h × c ÷ λ
- StepConvert the wavelength to metres — divide nanometres by a billion.
- StepEnter it; 500 nm becomes 0.0000005 and 1 nm becomes 0.000000001.
- ResultRead the energy in electronvolts; times 1.602176634 × 10⁻¹⁹ gives joules.
What this number means
Metres, not nanometres
The wavelength field takes metres, so 500 nm goes in as 0.0000005 and 1 nm as 0.000000001. Typing 500 lands far outside the range this page accepts, which stops at 0.001 m.
Short wavelength, high energy
The wavelength sits in the denominator of E = h × c ÷ λ, so halving it doubles the energy. Light at 1 µm carries 1.239842 eV and at 500 nm exactly twice that, 2.479684 eV.
A shortcut in electronvolts
h × c divided by the electron charge is 1.239841984 eV·µm. The energy in electronvolts is therefore that number divided by the wavelength in micrometres: 0.5 µm gives 2.479684 eV.
h and c are defined, not measured
This uses the exact SI values fixed in 2019: h = 6.62607015 × 10⁻³⁴ J·s, c = 299792458 m/s, one electronvolt at 1.602176634 × 10⁻¹⁹ J. No measurement uncertainty enters the result. The c here is the vacuum value; in glass or water light is slower.
Commonly misread
Green light is 500 nanometres, so I enter 500 in the wavelength field.
The field is in metres. 500 nm is 0.0000005 m, and that is the entry that gives 2.479684 eV.
Doubling the wavelength doubles the photon energy.
It halves it. Green light at 500 nm carries 2.479684 eV, and at 1 µm only 1.239842 eV.
The number this page returns is an energy in joules.
It is electronvolts, the handier scale when single photons land near 10⁻¹⁹ J. Multiply by 1.602176634 × 10⁻¹⁹ for joules.
Reference table
| Wavelength in m | Light | Photon energy in eV |
|---|---|---|
| 0.000001 | Near infrared, 1 µm | 1.239842 |
| 0.0000007 | Deep red, 700 nm | 1.771203 |
| 0.0000005 | Green, 500 nm | 2.479684 |
| 0.0000004 | Violet, 400 nm | 3.099605 |
| 0.000000001 | Soft X-ray, 1 nm | 1239.841984 |
Questions
How do I calculate the energy of a photon?
Multiply the Planck constant by the speed of light and divide by the wavelength, then divide the joules by the charge of one electron to get electronvolts. Green light at 500 nm comes out at 2.48 eV.
What is photon energy?
Light arrives in discrete packets called photons, and each one carries an energy fixed entirely by its wavelength. The unit is the joule, but single photons land around 10⁻¹⁹ J, so electronvolts are the handier scale.
Why do shorter wavelengths carry more energy?
The wavelength sits in the denominator of E = h × c ÷ λ, so halving it doubles the energy. That is why ultraviolet light can burn skin while infrared is only felt as warmth.
Which values of h and c does this use?
The exact SI values fixed in 2019: h = 6.62607015 × 10⁻³⁴ J·s and c = 299792458 m/s, with one electronvolt at 1.602176634 × 10⁻¹⁹ J. All three are defined rather than measured, so no uncertainty enters the result. The c here is the vacuum value; inside glass or water light is slower and the wavelength shorter.
Can I use frequency instead?
Yes, since E = h × f is the same relation. Frequency and wavelength are tied by c = λ × f, so convert first with the wavelength calculator and enter the result here.
Sources and last check
Information, not professional advice.