Photon energy converter
A 500 nm photon of visible light carries 2.479683968664 eV, oscillates at 599.584916 THz and sits at 20000 cm⁻¹. Move between energy, wavelength, frequency and wavenumber with the exact 2019 constants. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 500
- Source unit
- nm
- Target unit
- eV
- Result
- 2.4796839687
- From label
- nanometre
- To label
- electronvolt
- From kind
- wavelength
Photon energy, vacuum wavelength and frequency are three faces of the same light quantum. Planck’s relations E equals h times f and E equals h c over lambda link electronvolts to nanometres and terahertz with fixed physical constants, so a green laser line, an LED peak, an X-ray edge or a mid-infrared absorption band can be expressed in the unit your instrument, paper or homework asks for. This capability converts a positive quantity between energy units (eV, meV, keV, joule), wavelength units (nm, pm, micrometre, angstrom, metre), frequency units (Hz through THz) and spectroscopic wavenumber in reciprocal centimetres using the exact SI and CODATA 2019 values of h, c and the elementary charge. The path is fully deterministic: no network tables, no random seed and no wall clock.
What photon energy, wavelength and frequency mean and how they link
A photon carries energy E proportional to its frequency f through Planck’s constant h, written E equals h f. In vacuum the same photon has wavelength lambda related by the speed of light c as f equals c over lambda, so E also equals h c over lambda. Spectroscopy often reports wavenumber in reciprocal centimetres, which is one over the wavelength in centimetres and maps linearly onto energy.
Practically, visible light around five hundred nanometres sits near two and a half electronvolts, near-infrared bands sit below one electronvolt, and soft X-rays climb into the kiloelectronvolt range. Send the required field value as a finite positive number, plus from and to unit strings. Unknown unit names also fail with a clear message listing the supported set.
Supported units, exact constants, and how to read the response
Energy units include electronvolt, millielectronvolt, kiloelectronvolt, megaelectronvolt and joule. Wavelength units include nanometre, picometre, micrometre, angstrom and metre. Frequency units span hertz, kilohertz, megahertz, gigahertz and terahertz.
Wavenumber is accepted as cm-1, one slash cm, or reciprocal centimetre. Every conversion routes through energy in electronvolts using exact 2019 definitions: h is six point six two six zero seven zero one five times ten to the minus thirty-four joule-seconds, c is two hundred ninety-nine million seven hundred ninety-two thousand four hundred fifty-eight metres per second, and one electronvolt equals the elementary charge in joules.
What you can do with it
Optics homework and exam checks
Students convert a laser wavelength in nanometres to electronvolts and terahertz, compare with the textbook table, and get a clear error if they submit a zero or unknown unit.
Spectroscopy and instrument software
Pipelines normalise peak positions between eV, nm and cm⁻¹ for plots, databases and detector calibration without reimplementing Planck factors in every language.
LED, laser and filter datasheets
Product tools show centre wavelength, photon energy and frequency side by side for marketing pages, design reviews and procurement checklists.
FAQ
Which formula and constants does the converter use?
It uses E = h f = h c / λ with exact SI/CODATA 2019 values of Planck’s constant h, the speed of light c, and the elementary charge that defines the electronvolt. The constants object in the response lists the factors used.
What units are supported?
Energy: eV, meV, keV, MeV, J. Wavelength: nm, pm, um, angstrom, m. Frequency: Hz, kHz, MHz, GHz, THz. Wavenumber: cm-1.
Is the photon energy wavelength converter free?
The browser tool runs free on your device.
Why was my request rejected?
The error message names the problem and lists supported units for invalid unit names.
How many electronvolts is a 500 nm photon?
2.479683968664 eV. The same photon has a frequency of 599.584916 THz and a wavenumber of 20000 cm⁻¹, so one wavelength gives you all four descriptions of the light at once.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/conv/photon-energy \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":500,"from":"nm","to":"eV"}'const res = await fetch("https://api.kit.forhosting.com/conv/photon-energy", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 500,
"from": "nm",
"to": "eV"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/photon-energy",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 500,
"from": "nm",
"to": "eV"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/photon-energy", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":500,"from":"nm","to":"eV"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":500,"from":"nm","to":"eV"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/photon-energy", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"value": 500,
"from": "nm",
"to": "eV"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.photon_energy",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What photon energy, wavelength and frequency mean and how they link
Aliases amount and quantity for value, and unit_from, source, unit_to and target for the units, are accepted. Zero or negative values raise invalid_input because physical photon energy, wavelength, frequency and wavenumber must be greater than zero.
Supported units, exact constants, and how to read the response
On success the response echoes value, from, to, human labels and kinds, the converted result, plus summary fields energy_eV, wavelength_nm, frequency_THz, frequency_Hz and wavenumber_cm1 so UIs can show a full photon card without extra calls. The formula field summarises the path, method is always photon_planck_codata2019, and constants exposes h, c, e and the derived hc over e and h over e factors for transparency and homework write-ups. Missing fields, non-finite values, non-positive values and unknown units fail with invalid_input and are not charged.
API usage, pricing, lab workflows, and practical limits
Call the free in-browser photon energy wavelength converter for lecture demos, lab notebook checks, and quick unit swaps between eV, nm and THz without installing a CAS or a unit library. Extremely small or large inputs remain finite within ordinary double precision for classroom and lab ranges; pathological extremes that overflow to non-finite results are rejected. Authors shipping SDKs can map the summary fields directly into tables that list energy, wavelength, frequency and wavenumber for every converted line. Send a JSON body with required positive value, from unit and to unit. Use the prepaid API when an optics instrument dashboard, spectroscopy pipeline, curriculum generator, or materials database needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with a general energy converter when you must move bulk joules or kilowatt-hours, or with a wave-speed tool when the medium is not vacuum light.
Technical questions
How do I convert 500 nm light to electronvolts?
Send JSON with value 500, from "nm" and to "eV". The result is the photon energy in eV; energy_eV, frequency_THz and wavenumber_cm1 are also returned for convenience.