Luminance converter
Compare screen and projector brightness across old and modern units: 100 nits equal 29.186350796 foot-lamberts. Enter one luminance in nits, stilbs, lamberts, foot-lamberts or apostilbs and see it in all five at once. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Luminance magnitude to convert
- 100
- Input luminance unit
- nit
- Output luminance unit
- foot_lambert
- Result
- 29.186350796
- Nit
- 100
- Stilb
- 0.01
- Lambert
- 0.0314159265
Luminance conversion between SI candela per square meter and classic photometric units is a daily chore in display engineering, projection design, lighting surveys, and secondary-school optics homework. People search for a luminance converter when they need nits next to foot-lamberts for a monitor or cinema screen, or stilbs and lamberts next to apostilbs for an older textbook, not a general multi-unit toolbox that also handles length and temperature. This capability accepts one finite amount plus from and to unit labels among nit (cd/m²), stilb, lambert, foot-lambert, and apostilb, bridges every conversion through candela per square meter so results stay consistent, and returns the target value together with the same luminance expressed in all five units. Unrecognized unit names are rejected with a clear validation error instead of silently guessing a nearby symbol.
How the luminance converter maps photometric units through candela per square meter
Start from the candela per square meter as the SI coherent unit of luminance and express every other unit as a fixed factor into cd/m². One nit is exactly one candela per square meter, which is why display datasheets, HDR standards, and marketing copy that quote nits can be treated as SI without a scale change. One stilb is exactly one candela per square centimeter, which multiplies by ten thousand to reach candela per square meter because one square centimeter is one ten-thousandth of a square meter.
The lambert is defined as one over pi stilbs, so its factor into cd/m² is ten thousand over pi. The foot-lambert is defined as one over pi candela per square foot; with the international foot fixed at exactly zero point three zero four eight meters, one square foot is zero point three zero four eight squared square meters, and the foot-lambert factor is one over pi times that area.
The apostilb, also called the blondel, is defined as one over pi candela per square meter and is the metric counterpart of the foot-lambert for diffuse-surface photometry. This calculator never mixes those paths ad hoc. It multiplies the input amount by the factor of the source unit to reach cd/m², then divides by the factor of the target unit to produce the result.
Because every path shares the same intermediate, converting a five-hundred-nit panel to foot-lamberts and back, or comparing stilbs to apostilbs, stays numerically consistent within ordinary floating-point precision. The tool does not convert illuminance units such as lux or foot-candle, does not handle millilambert or skot as separate landings, does not apply display transfer curves or HDR metadata, and does not fetch live calibration databases.
It answers only the algebraic luminance unit conversion people mean when they type luminance converter into a search bar and expect nit, stilb, lambert, foot-lambert, and apostilb.
Where dedicated luminance conversion shows up in real work
Secondary-school and college physics and optics courses constantly assign problems that give a surface luminance on one scale and ask for another, often mixing textbook stilbs and lamberts with SI nits and cinema-style foot-lamberts in the same worksheet. Display and television engineers compare monitor and television peak brightness quoted in nits against older projection and film standards that still list foot-lamberts for screen luminance, so a single conversion pass keeps datasheets, review reports, and color-grading notes aligned.
Architectural and stage lighting designers step between apostilbs for diffuse-surface metrics and candela per square meter for SI-native models without reimplementing factors in every spreadsheet. Data pipelines that ingest mixed photometric reports can call this capability once per reading instead of reimplementing the pi and foot factors in every service. If you later need illuminance conversion, density conversion, mass-only conversion, or general multi-category unit conversion, treat those as separate search intents and landings rather than overloading this luminance converter page.
What you can do with it
Display and HDR datasheets
Convert monitor and TV peak brightness between nits (cd/m²) and foot-lamberts so SI reports and cinema-style reviews stay consistent.
Optics homework and textbooks
Map stilbs, lamberts, and apostilbs to candela per square meter for lab write-ups and auto-graded problem sets.
Lighting surveys and calibration logs
Normalize mixed fL, asb, and cd/m² tags from meters and field notes into one SI-native column for analysis.
FAQ
Which luminance units does this converter support?
Nit (cd/m²), stilb, lambert, foot-lambert (fL), and apostilb (asb).
What happens if I send an unrecognized unit?
The error message includes Unrecognized unit and lists the supported families so you can correct the label.
Is a nit the same as cd/m²?
Yes. One nit is exactly one candela per square meter. The converter treats both labels as the same SI unit.
How does 1 stilb relate to nits?
Exactly 10,000 nits. One stilb is one candela per square centimeter, and one square centimeter is 10⁻⁴ square meters.
What does it cost?
The browser tool is free and runs locally.
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/luminance \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"amount":100,"from":"nit","to":"foot_lambert"}'const res = await fetch("https://api.kit.forhosting.com/conv/luminance", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"amount": 100,
"from": "nit",
"to": "foot_lambert"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/luminance",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"amount": 100,
"from": "nit",
"to": "foot_lambert"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/luminance", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"amount":100,"from":"nit","to":"foot_lambert"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"amount":100,"from":"nit","to":"foot_lambert"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/luminance", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"amount": 100,
"from": "nit",
"to": "foot_lambert"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.luminance",
"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 you send and what you get back from the API and browser form
Send three fields: amount, a finite number for the luminance magnitude; from, a string naming the input unit; and to, a string naming the output unit. When a unit string is unknown the error message includes Unrecognized unit and lists the five supported families so clients can fix the label rather than guessing. Classic checks include one stilb becoming ten thousand nits, one lambert becoming ten thousand over pi nits, one foot-lambert becoming about three point four two six nits, and one apostilb becoming one over pi nits. Both unit fields accept short keys and everyday words in any common casing, including nit or nits or cd/m2 or candela per square meter, stilb or sb or cd/cm2, lambert or L, foot_lambert or fL or foot-lambert or ft-L, and apostilb or asb or blondel. Missing fields, non-numeric amount strings, NaN, Infinity, and unrecognized unit labels fail with invalid_input and are not charged. On success the response echoes the cleaned amount, normalized from and to keys, the primary result in the target unit, the same luminance as nit, stilb, lambert, foot_lambert, and apostilb with twelve significant digits of stable precision, the SI factors used, the formula string, and method cd_m2_bridge. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where dedicated luminance conversion shows up in real work
Calibration and quality-control workflows normalize mixed IoT or lab payloads that tag readings as cd/m2, fL, or asb before archiving or comparison. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.