Light meter for film photographers · Android
A light meter that knows your film.
Lumen turns your phone camera into a reflected and incident meter, corrects long exposures for the stock you loaded, and logs every frame of the roll. No account, no ads, and the meter works offline.
ISO 6–12800f/1.0–321/8000 s to 8 min⅓ stop steps11 film stocks
How a reading works
From the scene in front of you to a frame on the roll.
- Aim and tapChoose spot, centre-weighted, average or incident. Tap the frame to spot-meter that exact point.
- Lumen measuresIt averages the frame in linear light and reads the camera’s own exposure data to give an EV in ⅓ stops.
- Choose what stays fixedAperture or shutter priority. Lumen solves the other side and tells you when the lens runs out of stops.
- Correct for the filmPast one second, film loses speed. Metered 10 s on HP5 Plus becomes the 20 s it actually needs.
- Log the frameHold the shutter button to log aperture, shutter, EV and a note, then advance. Export the roll as CSV.
Try a reading
The same exposure maths the app runs.
Set the light, the film and what you want to keep fixed. Lumen picks the nearest marked speed or stop, and tells you what the film needs past one second.
- HP5 Plus needs no reciprocity correction at 1/250. It starts past 1 s.
Reciprocity uses each stock’s published or community-measured curve. Treat long exposures as a starting point and bracket.
What’s in the meter
Built for the person holding a mechanical camera.
Four metering modes
Spot, centre-weighted and average through the rear camera. Incident through the front camera under a diffuser.
Film library
HP5, FP4, Pan F, Delta 3200, Tri-X, T-Max, Portra, Ektar, Gold, Velvia and Acros II, each with its box speed and process.
Reciprocity
Each stock carries its own correction curve. Long exposures come out at the time the film needs, not the time the meter says.
Roll log
Every frame keeps aperture, shutter, EV, film, push or pull, and a note. Export a roll as CSV for your scans.
Zone overlay
Pinch to see the frame mapped into Zone System values, so you know where shadows and highlights will land.
Calibration
Phones differ. Set an offset in ⅓ stops against a grey card or a handheld meter, and Lumen keeps it.
Gestures, with buttons
Tap, drag and pinch on the frame for speed. Every gesture also has a visible control, and targets are 44 dp or larger.
Offline first
Metering, films, logging and sun times run on the phone. No account, no ads, no analytics.
Your thumb does the work. Buttons still do too.
Gestures are a shortcut, never the only way. Each one has a visible control beside it, and you can switch gestures off.
| Gesture | What it does | Button for the same thing |
|---|---|---|
| Tap the frame | Spot-meter that point | Metering mode buttons |
| Drag left / right | Walk equivalent pairs, f/8 1/125 to f/11 1/60 | Aperture wheel |
| Drag up / down | Calibration offset in ⅓ stops | Calibration field |
| Two-finger drag | ISO, 6 to 12800 | ISO chip |
| Double-tap | Lock the reading before you lower the phone | Lock chip |
| Pinch | Zone overlay on and off | Zone chip |
| Hold the shutter | Log the frame and advance | Short press logs only |
| Edge swipe | Previous or next screen | Tab bar |
Looks
Dress the meter like the camera in your other hand.
Sixteen palettes named after the towns where cameras and film were made, and four surface styles. Pick one below and the phone changes with it.
Surface
Theme
Theme names refer to places. Lumen uses no camera or film maker’s name, logo or trademark in its themes, and is not affiliated with any of them. Safelight dims the screen to red for the darkroom; Bleach is for reading in full sun.
Simple and Advanced
The meter stays quiet until you ask for more.
Simple
The meter, the film and the roll. Nothing else on screen while you are about to shoot.
Advanced
Adds a Light screen with UV, cloud, colour temperature, flicker and the sun’s path, plus filter suggestions. Turn it on in Look.
Measured by your camera
- Exposure value, in ⅓ stops
- Colour temperature, estimated in kelvin
- Mains flicker, present or not
- Scene contrast, in stops
On the phone. Nothing leaves it.
Calculated on the phone
- Sun altitude and direction
- Sunrise and sunset
- Golden hour and blue hour
Solar position maths. Works offline.
Reported for your area
- UV index
- Cloud cover
From OpenWeatherMap, for a location rounded to about 1 km.
The sun over Cimahi, 7 October 2026
Sunrise 05:32Golden until 06:00Golden from 17:16Sunset 17:44Blue hour ends 18:05
Golden hour, sun below 6°Blue hour, 4° to 6° below the horizonCalculated in your browser with the solar formulas Lumen uses on the phone.
Privacy
Your rolls stay on your phone.
Never leaves the phone
- Camera frames. Lumen reads brightness from the preview and keeps no images.
- Your rolls, frames and notes.
- Your precise location. Lumen only asks for approximate location.
Sent only in Advanced mode
- Approximate coordinates, rounded to about 1 km, sent to OpenWeatherMap over HTTPS to get UV and cloud cover.
- Nothing else. There is no account, no analytics and no advertising SDK.
Pricing
Free to meter. Pay once for the rest.
No subscription. Lumen Pro is a single in-app purchase that stays yours.
Lumen
FreeEverything you need to expose a roll
- All four metering modes
- Aperture and shutter priority
- Film library with reciprocity
- Roll and frame log
- Calibration offset
Lumen Pro
One-time purchasePrice set at launch on Google Play
- All 16 themes and 4 surface styles
- Advanced mode: UV, cloud, colour temperature, flicker, sun path
- CSV export of rolls
- Zone System overlay
Version 0.1 · Internal test
Help calibrate Lumen before it ships.
Lumen is in testing on Android. Metering accuracy is still being checked across phones, so please don’t trust it with a roll you care about yet. Compare it with a handheld meter or a grey card in bright, medium and dim light, and send us the numbers.
Questions
Before you load a roll.
How accurate is a phone light meter?
A phone camera measures reflected light well once it is calibrated, but every phone is a little different. Lumen lets you set an offset in ⅓ stops against a grey card or a handheld meter. While Lumen is in testing, check its readings before you rely on them.
Does it need an internet connection?
No. Metering, the film library, reciprocity, the roll log and sun times all work offline. Only Advanced mode goes online, to fetch UV and cloud cover.
Which phones does it run on?
Android 8.0 or newer with a rear camera. Incident metering uses the front camera, so you need a small white diffuser over it.
What is reciprocity failure?
Film gets less sensitive during long exposures. Past about one second, a metered 10 s exposure on HP5 Plus needs about 20 s. Lumen applies the correction for the stock you choose.
Why are the themes named after cities?
Each palette nods to the industrial design of a place where cameras or film were made. Lumen does not use any maker’s name, logo or trademark, and it is not affiliated with any of them.
Is there an iPhone or Wear OS version?
Lumen is Android only for now. A Wear OS companion is planned after the phone app is stable.