Photon Energy Calculator
Photon energy in eV and joules from wavelength, with frequency.
What it does
Light arrives in packets whose energy sets color: long red waves carry near 1.77 eV while short violet ones carry 3.26. One equation prices them all, Planck constant times light speed over wavelength.
The tool above takes wavelength in nanometers. It returns electron volts with joules and frequency beside it. The default 500 nm green photon carries 2.48 eV (3.9729e-19 J) at 5.9958e+14 Hz.
Forms and constants match NIST with OpenStax beside them: E is hf is hc over lambda, h is 6.62607015e-34 exact, c is 299792458 exact, and hc is 1240 eV nm. Worked checks agree, from 100 nm at 12.4 eV to the 580 nm average at 3.4249e-19 J.
Shorter means hotter per photon but says nothing about beam power. A dim blue lamp and a bright red heater differ in photon counts, so multiply per photon energy by rate for watts.
How to use
- Type wavelength in nanometers.
- Read eV first, joules beside it.
- Read frequency for wave context.
- Shortcut check: 1240 over nm.
- Compare colors inside visible 380 to 700.
- Multiply by photons per second for power.
Formula
- h
- Planck constant 6.62607015e-34 J s, exact.
- c
- Light speed 299792458 m/s, exact.
- lambda
- Wavelength in meters inside the math.
SI constants are exact by definition, so digits reflect input precision only. Frequency follows from the same pair with no extra data.
Worked example
Example: 500 nm green
Default input: 500 nm.
- Meters: 500 nm is 500e-9 m.
- Numerator: h x c is 1.98644586e-25 J m.
- Joules: / 500e-9 = 3.9729e-19 J.
- eV: / 1.602176634e-19 = 2.48 eV.
- Shortcut: 1240 / 500 = 2.48, matching.
- Tool shows 2.48 eV, 3.9729e-19 J, 5.9958e+14 Hz.
Reference table
| Wavelength | Energy | Anchor |
|---|---|---|
| 100 nm UV | 12.4 eV | OpenStax example |
| 380 nm violet | 3.26 eV | Visible edge |
| 500 nm green | 2.48 eV | Default case |
| 580 nm | 2.14 eV | 3.4249e-19 J |
| 700 nm red | 1.77 eV | Visible edge |
Limits
- Vacuum wavelengths; media shift slightly.
- Single photon; beam power needs rate.
- Nonrelativistic matter excluded.
- Input precision caps digits.
Common mistakes
- Plugging nm as meters, off by a billion.
- Reading eV as volts.
- Confusing per photon with per second.
- Using 1240 past its shortcut precision.
- Comparing colors outside visible by habit.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 nm?
12.4 eV.
580 nm in joules?
3.4249e-19 J.
Zero input?
Rejected: enter 0.001 to 1000000000000 nm.
Questions
Green photon energy?
2.48 eV at 500 nm.
Shortcut?
eV is about 1240 over nanometers.
Red versus violet?
1.77 eV at 700 nm against 3.26 at 380.
Joules scale?
Near 1e-19 J per visible photon.
Frequency of green?
5.9958e+14 Hz.
Wavelength page versus this?
That converts wave units; this prices photon energy.