3.9729e-19
J
2.4797
eV
239.25
kJ/mol
500
nm
5.9958e+14
Hz
20,000
cm⁻¹
3.9729e-19
J
2.4797
eV
239.25
kJ/mol
500
nm
5.9958e+14
Hz
20,000
cm⁻¹
Photon energy is the fundamental quantum of electromagnetic radiation energy, first described by Max Planck in 1900 and further developed by Albert Einstein in his 1905 explanation of the photoelectric effect. The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength, connected through the famous relation E = hf = hc/λ. The Photon Energy Calculator converts between wavelength, frequency, and energy in multiple units (joules, electron volts, kJ/mol, wavenumber). This relationship is central to virtually every area of physics and chemistry: spectroscopy uses photon energies to probe molecular and atomic structure; photovoltaics requires photon energy exceeding the band gap for electricity generation; photochemistry depends on photon energy to drive reactions; and medical imaging uses high-energy photons for diagnostics. Whether working with radio waves (μeV), visible light (~2 eV), or gamma rays (MeV), this calculator provides instant conversion between all relevant units.
The energy of a single photon is given by the Planck-Einstein relation:
$$E = h\nu = \frac{hc}{\lambda}$$
where h = 6.626 × 10⁻³⁴ J·s is Planck's constant, ν is the frequency (Hz), c = 2.998 × 10⁸ m/s is the speed of light, and λ is the wavelength.
Unit conversions:
$$E \text{ (eV)} = \frac{E \text{ (J)}}{1.602 \times 10^{-19}}$$
$$E \text{ (kJ/mol)} = E \text{ (J)} \times N_A / 1000$$
The wavenumber (cm⁻¹) is widely used in IR spectroscopy:
$$\tilde{\nu} = \frac{1}{\lambda \text{ (cm)}} = \frac{\nu}{c}$$
Useful conversions: 1 eV = 1240 nm = 8065.5 cm⁻¹ = 96.49 kJ/mol = 2.418 × 10¹⁴ Hz.
The energy output tells you the energy carried by a single photon. Visible light photons carry about 1.8–3.1 eV: red light (~700 nm) has ~1.77 eV, while violet (~400 nm) has ~3.1 eV. UV photons (10–400 nm) have 3.1–124 eV, enough to break chemical bonds and cause sunburn. X-rays (0.01–10 nm) carry 124 eV to 124 keV, enabling medical imaging. The kJ/mol unit is useful for comparing photon energies with chemical bond energies: a C-C bond (~346 kJ/mol) requires UV photons below ~346 nm to break photolytically. The wavenumber output is the standard unit in infrared spectroscopy, where molecular vibrations typically absorb at 400–4000 cm⁻¹. Higher wavenumber means higher energy.
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A green photon at 500 nm has energy 2.48 eV (239 kJ/mol), enough to drive photosynthesis and some photochemical reactions.
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Microwave oven radiation at 2.45 GHz has only ~10 μeV per photon — far too low to break bonds. Heating occurs through dielectric rotation of water molecules.
E = hν = hc/λ states that photon energy is proportional to frequency and inversely proportional to wavelength. This was the first quantum hypothesis: Planck proposed energy quantization in 1900 to explain blackbody radiation, and Einstein applied it to light in 1905.
Visible light spans ~380–700 nm, corresponding to energies of 1.77 eV (red) to 3.26 eV (violet). The human eye is most sensitive near 555 nm (green-yellow, ~2.24 eV).
Wavenumber (cm⁻¹) = 1/λ(cm) is proportional to energy and frequency. It is the standard unit in infrared spectroscopy because it gives a linear energy scale. Common vibrations: O-H stretch ~3400 cm⁻¹, C=O stretch ~1700 cm⁻¹, C-H stretch ~2900 cm⁻¹.
Use the formula: E(eV) = 1240/λ(nm), or equivalently λ(nm) = 1240/E(eV). This comes from E = hc/λ with h and c in appropriate units.
Bond energies and reaction enthalpies are typically reported in kJ/mol. Comparing photon energy in kJ/mol to bond dissociation energies tells you whether a photon has enough energy to break a specific bond photochemically.
The minimum photon energy needed to eject an electron from a material surface. For most metals, this is 2–5 eV (corresponding to UV light). Below this threshold, no electrons are emitted regardless of light intensity.
A solar cell absorbs photons with energy ≥ the semiconductor band gap (1.1 eV for Si). Lower-energy photons pass through; higher-energy photons lose excess energy as heat. This limits single-junction solar cell efficiency to ~33% (Shockley-Queisser limit).
X-rays: 100 eV – 100 keV (λ = 12.4 nm – 0.0124 nm). Gamma rays: > 100 keV (λ < 0.0124 nm). Medical X-rays typically use 20–150 keV photons. Nuclear gamma rays range from hundreds of keV to several MeV.
Yes, if its energy exceeds the bond dissociation energy. UV photons (200–400 nm, 3–6 eV) can break many single bonds. This is the basis of photodissociation in atmospheric chemistry (e.g., O₃ photolysis) and photochemistry.
Color is our perception of photon energy: Red (~1.8 eV), Orange (~2.0 eV), Yellow (~2.1 eV), Green (~2.3 eV), Blue (~2.6 eV), Violet (~3.1 eV). Objects appear colored because they absorb certain photon energies and reflect/transmit others.
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