Luminous exposure converter
Add up light over time in the unit your log uses: 3600 lux seconds make exactly 1 lux hour. Five exposure units, from millilux seconds to phot hours, for museum light-dose records, daylighting studies and photometry homework. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 3,600
- From
- lx·s
- To
- lx·h
- Result
- 1 lx·h
- Converted
- 1
- Value lx s
- 3,600
- Factor
- 0.0002777778
A luminous exposure converter turns one H = E × t magnitude into another photometric time-integrated unit without spreadsheet hour-second tables or hand-written phot-to-lux powers of ten. Enter a finite value plus a source unit and a target unit among lux seconds, lux hours, phot seconds, phot hours, and millilux seconds; the tool returns the converted exposure, the SI intermediate in lux·seconds, the exact unit factor applied, and step-by-step substitution lines you can paste into a lighting schedule, museum conservation log, photographic lab notebook, or product datasheet. Conservation scientists comparing cumulative light dose on artworks, architects integrating lux over operating hours, students converting photometry homework, and firmware authors mapping sensor counts to physical exposure all need the same deterministic path.
Which luminous exposure units are supported and how conversion works
This capability converts among five everyday luminous-exposure units that dominate museum conservation, architectural daylighting, photographic photometry, and laboratory coursework. Luminous exposure H is illuminance integrated over time: the SI coherent product is the lux second (lx·s), and that quantity is the internal hub for every conversion. Lux hours use the exact civil hour of three thousand six hundred seconds, so one lx·h equals three thousand six hundred lx·s.
Phot seconds use the exact CGS phot definition of ten thousand lux, so one ph·s equals ten thousand lx·s. Phot hours combine both exact factors into thirty-six million lx·s. Millilux seconds use the exact SI milli prefix of one thousandth of a lux·second.
Middle dots, spaces, hyphens, and multiplication signs between the illuminance and time tokens are normalized away before matching. Same-unit requests succeed and return the input magnitude with a short message that no change of unit was required.
Practical tips, limits, and when to use this landing
Prefer sending bare numbers for value when you control the client; string numbers are accepted only when they match a strict finite numeric pattern without currency symbols or thousand separators. Round-trip checks are straightforward: convert A to B and B back to A and confirm you recover the original within the published twelve-decimal rounding. When teaching SI and CGS photometry, pair classic examples such as three thousand six hundred lux·seconds to one lux·hour, ten thousand lux·seconds to one phot·second, and one phot·hour to thirty-six million lux·seconds.
Stay inside the absolute range so intermediate lux·second values cannot overflow. This landing targets people searching for a luminous exposure converter, lux seconds to lux hours, phot seconds to lux seconds, or millilux seconds converter online; it is not a general multi-quantity unit converter, not a luminous flux (lm) tool, not a bare illuminance-only calculator without time, and not a camera EV estimator.
What you can do with it
Museum and archive light-dose logs
Conservators convert cumulative lux·hour readings into lux·seconds or phot·seconds so multi-year exhibition logs stay comparable across instruments and lab standards.
Architectural daylighting schedules
Designers integrate room lux over operating hours into lx·h totals, then convert to SI lux·seconds for simulation tools and code compliance tables.
Photometry homework and lab notes
Students convert lx·s, lx·h, and ph·s homework values with deterministic steps they can compare against hand calculations before submission.
FAQ
How many lux·seconds are in one lux·hour?
Exactly 3600. One phot·second is exactly 10 000 lux·seconds because one phot equals 10 000 lux by definition.
Is the luminous exposure converter free?
The browser tool is free and runs locally.
Does this convert luminous flux or bare lux?
No. It only converts luminous exposure (illuminance × time) among the five supported units. Flux (lm) and bare illuminance without a time base are different quantities.
How many lux seconds is one phot second?
Ten thousand. The phot is the old CGS unit equal to ten thousand lux, so one phot second is ten thousand lux seconds, and one phot hour is thirty-six million lux seconds.
What does luminous exposure measure?
It measures how much light a surface has received over time: illuminance multiplied by duration. Conservators track it as a cumulative light dose on artworks, and architects use it to add up lux over operating hours.
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/luminous-exposure \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":3600,"from":"lx·s","to":"lx·h"}'const res = await fetch("https://api.kit.forhosting.com/conv/luminous-exposure", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 3600,
"from": "lx·s",
"to": "lx·h"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/luminous-exposure",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 3600,
"from": "lx·s",
"to": "lx·h"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/luminous-exposure", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":3600,"from":"lx·s","to":"lx·h"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":3600,"from":"lx·s","to":"lx·h"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/luminous-exposure", 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": 3600,
"from": "lx·s",
"to": "lx·h"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.luminous_exposure",
"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.
Limits
max_abs | 1000000000000 |
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
Unknown unit names fail with a clear invalid_input error instead of silent wrong factors.
Which luminous exposure units are supported and how conversion works
Every request multiplies the input by how many lux·seconds equal one source unit, then divides by how many lux·seconds equal one target unit. Common aliases are accepted case-insensitively: lux second and lux seconds for lx·s, lux hour and lux hours for lx·h, phot second and phot seconds for ph·s, phot hour and phot hours for ph·h, millilux second and millilux seconds for mlx·s. If the name is not on that list the solver rejects the request with invalid_input naming the bad field and listing supported units, so clients never guess whether a typo produced a wrong number. Negative values are allowed only for signed arithmetic contexts you may choose to model; absolute magnitude must stay within the published one-trillion limit so intermediate products remain finite in IEEE double precision on the Worker and in the browser. This tool deliberately stays on the luminous-exposure axis: it does not convert bare lux without a time base, lumens of flux, candela of intensity, or photographic exposure value EV, which are different photometric quantities with different SI dimensions.
How to call the API and read the response
Value must be a finite number or a strict numeric string within absolute limits of one trillion. Wire this into dashboards, mobile clients, or batch jobs that already hold a cumulative light-dose reading and only need a second unit for display, conservation logs, or regulatory comparison without shipping floating conversion tables in every app binary. Send a JSON body with three required fields: value (aliases exposure, amount, H, and dose), from (aliases from_unit, unit_from, and source), and to (aliases to_unit, unit_to, and target). From and to must resolve to supported unit names after alias normalization. On success the response echoes the rounded input value, canonical from and to labels, result and converted set to the same rounded target magnitude, value_lx_s as the SI intermediate in lux·seconds, unit as the target label, factor as the from-to multiplier, formula as the short equation string, message as an English summary, steps as ordered substitution lines, and supported_units as the five canonical identifiers. Failed validation—missing fields, non-finite numbers, values outside absolute limits, or an unknown unit name—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and when to use this landing
Normalize display labels on your side if you need locale-specific spellings—this API always returns the short canonical tokens lx·s, lx·h, ph·s, ph·h, and mlx·s so automated tests stay stable. Prefer this capability when both endpoints are among the five supported luminous-exposure units and you need deterministic factors and step strings; if you need flux in lumens, bare lux on a surface without integrating time, or candela at a solid angle, use a dedicated photometric calculator instead. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when clients deliberately probe unknown unit names.
Technical questions
Which luminous exposure units can I convert?
Lux seconds (lx·s), lux hours (lx·h), phot seconds (ph·s), phot hours (ph·h), and millilux seconds (mlx·s), including common full-word aliases such as lux hour and phot seconds.
What happens if I send an unknown unit name?
The API returns invalid_input, names the bad field, and lists the supported units. The failed task is not charged.