Can I measure lux with my phone camera?

Roughly. Camera-based apps calculate lux from the camera’s exposure settings, so the reading jumps in steps: by more than half the value below 100 lux, and by less than 5% above 1,000 lux (Odenwald, 2020). Point the camera at the sky, never at the sun.

Why does my lux meter app show a different number than a light meter?

The phone has no white diffusing dome like a light meter, and every app and phone combination needs its own calibration (Odenwald, 2020). Without that calibration, expect the app to differ from a real light meter.

Do lux meter apps work on iPhone?

They work differently there. On iPhones, apps have restricted access to the light sensor (Gardasevic et al., 2022). Most iPhone apps in a 2020 study used the back camera instead, and camera readings were least precise in dim light (Odenwald, 2020).

Is a lux meter app good enough to check if I get daylight?

It can show large differences, such as indoors versus outdoors, which phone sensors track reasonably well (Gardasevic et al., 2022). It cannot show melanopic EDI, the measure expert light recommendations use (Brown et al., 2022).

Does LightOtter measure lux?

Not precisely. The brightness check in the app gives a quick estimate from the camera, not a calibrated reading. The daily minutes are a rule of thumb from the clouds and the height of the sun.

Guide · Light

Lux meter apps: how accurate is your phone as a light meter?

Your phone can read lux from its camera or from a small light sensor on the front. The number looks exact, but in tests it depended on the phone, the app and how bright it was.

LightOtter editorial team · reviewed against the sources below · 14 October 2026 · Who is behind it

The short answer

How accurate is a lux meter app?

A lux meter app gives a rough reading, not an exact one. In a peer-reviewed test, uncalibrated phone readings were clearly too high or too low. After the author calibrated one app against a reference meter, the remaining error was about ±12% above 5,000 lux and ±18% below 100 lux (Odenwald, 2020).

How accurate are lux meter apps in a calibration test?

A 2020 peer-reviewed study compared two Android phones and one iPhone, models from 2015 and 2017, with a reference light meter that has a stated accuracy of ±5%. The phones measured sunlight reflected off a white foamboard outdoors (Odenwald, 2020).

The phone readings showed over- and underestimates. The author then fitted separate calibration curves for bright, medium and low light. For one camera-based app on the iPhone, this error remained after calibration (Odenwald, 2020):

Bright sunlight, 5,000 to 500,000 lux: about ±12%
Shade and indoors, 100 to 5,000 lux: about ±16%
Dawn and twilight, 0 to 100 lux: about ±18%

Why does the same app show different numbers on different phones?

In the study, the calibration had to be repeated for each combination of app and phone, because apps that use the camera and apps that use the light sensor scale their readings differently. The same app on two Android models gave similar results in bright light, around 16,300 lux, and very different ones at about 114 lux (Odenwald, 2020).

A 2022 study exposed one Android phone to calibrated light in a dark box. Its readings followed the true values closely but came out slightly low at the brighter settings. The authors judged phone light sensors unlikely to match a fully calibrated lux meter, but probably good enough to track large changes in light (Gardasevic et al., 2022).

Camera or light sensor: why do phone readings differ?

Most iPhone apps in the 2020 study calculated lux from the back camera’s exposure data. Most Android apps read the dedicated light sensor on the front of the phone, next to the front camera (Odenwald, 2020). On iPhones, apps have restricted access to that sensor (Gardasevic et al., 2022).

Camera: the reading jumps in steps whenever the camera changes aperture, exposure time or ISO. Below 100 lux a jump can be more than half the value; above 1,000 lux the uncertainty drops below 5% (Odenwald, 2020).
Light sensor: it reports a smooth stream of values, but the phone has to face you while you read it, so your own shadow can spoil the reading (Odenwald, 2020).
No diffuser: the reference meter collects light through a white dome, the phones had nothing over the lens. The author names this as one important reason why the phone scale was off (Odenwald, 2020).

Can a lux meter app show melanopic lux?

No. A phone measures plain illuminance, not melanopic light. It also measures in the direction it points, which is roughly opposite to where you look while you read the screen (Gardasevic et al., 2022).

Expert recommendations for daytime and evening light are given as melanopic EDI at the eye, measured in the vertical plane at about 1.2 m height (Brown et al., 2022). Common electric lighting is much less effective at stimulating the eye’s melanopsin cells than daylight of the same illuminance (Brown et al., 2022). A lamp and daylight with the same lux reading are therefore not equal on this measure, and a lux meter app cannot tell them apart.

How bright is daylight? Lux values outdoors and indoors, compared.

How does LightOtter estimate brightness?

The LightOtter app has a brightness check. You point the back camera at the sky, never at the sun, and tap to get a quick estimate in lux. The app says it plainly: a phone camera can only estimate brightness, which is good enough for “indoors or outdoors?” but is not a calibrated meter. In the settings, a calibration value evens out your phone camera.

The light check on this website uses no sensor at all. Your answers about a usual weekday and the position of the sun give an estimate, not a measurement.

The daily minutes outside are a LightOtter rule of thumb based on the clouds and the height of the sun where you are. They are estimated, not measured.

Six questions, one minute: the LightOtter light check for your day.

How to get a more useful reading from a lux meter app

Read the number as a comparison, not as an exact value. These habits follow from the limits the studies describe:

Compare places with the same phone and app, for example by the window and in the middle of the room. Large differences are what phone light sensors track reasonably well (Gardasevic et al., 2022).
Don’t compare readings across phones or apps. In the 2020 study, a calibration held only for one app on one phone (Odenwald, 2020).
Be careful with low readings. Below 100 lux the error after calibration was largest (Odenwald, 2020).
With an app that uses the front sensor, keep your hand and your shadow away from it (Odenwald, 2020).
Point the camera at the sky, never at the sun.

How LightOtter works out its minutes, and what that rests on.

What this is not

This guide is about how phones measure light. It is not medical advice, and LightOtter is neither a medical device nor a calibrated measuring instrument. If you feel tired for a long time, talk to a doctor. Never look directly at the sun.