{
    "name": "Photon Energy Calculator",
    "url": "https://calculators.geekmidst.com/calculators/photon-energy-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/photon-energy-calculator.md",
    "category": "Science & engineering",
    "description": "Find the energy of a photon from its wavelength, frequency or energy in eV with E = hf = hc/λ, using the exact SI values of h, c and the elementary charge.",
    "summary": "A photon’s energy depends only on its frequency: E = h × f = h × c ÷ λ. Shorter wavelengths carry more energy per photon.",
    "also_called": [
        "Planck relation calculator",
        "Wavelength to electronvolt converter"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "from",
            "label": "Start from",
            "type": "segmented",
            "default": "wavelength",
            "options": {
                "wavelength": "Wavelength",
                "frequency": "Frequency",
                "energy_ev": "Energy (eV)"
            }
        },
        {
            "name": "wavelength",
            "label": "Wavelength (in vacuum)",
            "type": "number",
            "default": "500",
            "shown_when": {
                "from": "wavelength"
            }
        },
        {
            "name": "wavelength_unit",
            "label": "Wavelength unit",
            "type": "select",
            "default": "nm",
            "options": {
                "nm": "nm",
                "um": "µm",
                "mm": "mm",
                "cm": "cm",
                "m": "m",
                "km": "km"
            },
            "shown_when": {
                "from": "wavelength"
            }
        },
        {
            "name": "frequency",
            "label": "Frequency",
            "type": "number",
            "default": "600",
            "shown_when": {
                "from": "frequency"
            }
        },
        {
            "name": "frequency_unit",
            "label": "Frequency unit",
            "type": "select",
            "default": "THz",
            "options": {
                "Hz": "Hz",
                "kHz": "kHz",
                "MHz": "MHz",
                "GHz": "GHz",
                "THz": "THz"
            },
            "shown_when": {
                "from": "frequency"
            }
        },
        {
            "name": "energy_ev",
            "label": "Photon energy",
            "type": "number",
            "default": "2",
            "unit": "eV",
            "shown_when": {
                "from": "energy_ev"
            }
        }
    ],
    "outputs": [
        {
            "key": "energy_ev",
            "label": "Energy per photon",
            "format": "number"
        },
        {
            "key": "energy_j",
            "label": "Energy per photon (joules)",
            "format": "text"
        },
        {
            "key": "kj_per_mol",
            "label": "Energy per mole of photons",
            "format": "number"
        },
        {
            "key": "wavelength",
            "label": "Wavelength",
            "format": "text"
        },
        {
            "key": "frequency",
            "label": "Frequency",
            "format": "text"
        }
    ],
    "formula": {
        "text": "E = h × f = h × c ÷ λ;  E(eV) = E(J) ÷ e;  E per mole = E × N_A",
        "variables": {
            "h": "Planck constant, 6.62607015 × 10⁻³⁴ J·s (exact)",
            "c": "speed of light, 299,792,458 m/s (exact)",
            "e": "elementary charge, 1.602176634 × 10⁻¹⁹ C (exact)",
            "N_A": "Avogadro constant, 6.02214076 × 10²³ mol⁻¹ (exact)",
            "λ": "vacuum wavelength",
            "f": "frequency"
        }
    },
    "worked_example": {
        "inputs": {
            "from": "wavelength",
            "wavelength": "500",
            "wavelength_unit": "nm",
            "frequency": "600",
            "frequency_unit": "THz",
            "energy_ev": "2"
        },
        "steps": [
            "hc = 6.62607015 × 10⁻³⁴ × 299,792,458 = 1.98645 × 10⁻²⁵ J·m.",
            "E = 1.98645 × 10⁻²⁵ ÷ (500 × 10⁻⁹ m) = 3.97289 × 10⁻¹⁹ J.",
            "E = 3.97289 × 10⁻¹⁹ ÷ 1.602176634 × 10⁻¹⁹ = 2.4797 eV."
        ],
        "result": "A 500 nm (green) photon carries about 2.48 eV, or 3.97 × 10⁻¹⁹ J."
    },
    "interpretation": "A handy shortcut is E (eV) ≈ 1239.84 ÷ λ (nm). Compare the result with a material’s band gap or work function to see whether light of that colour can excite electrons or eject them (the photoelectric effect).",
    "assumptions": [
        "Wavelength is the vacuum wavelength. All four constants are the exact defining values of the 2019 SI."
    ],
    "limitations": [
        "In a medium the wavelength is shorter but the photon energy is unchanged; enter the vacuum wavelength or the frequency."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why is energy per mole useful?",
            "answer": "It puts photon energies on the same scale as chemical bond energies (typically 150–1,000 kJ/mol), showing which light can break which bonds."
        },
        {
            "question": "What is 1 eV in wavelength?",
            "answer": "About 1,239.84 nm, in the near infrared."
        }
    ],
    "sources": [
        {
            "title": "NIST (National Institute of Standards and Technology)",
            "url": "https://www.nist.gov/"
        }
    ],
    "related": [
        {
            "name": "Frequency and Wavelength Calculator",
            "url": "https://calculators.geekmidst.com/calculators/frequency-wavelength-calculator"
        },
        {
            "name": "Thin Lens Equation Calculator",
            "url": "https://calculators.geekmidst.com/calculators/optical-lens-equation-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}