LUX Meter
Support and FAQ
Answers about accuracy, calibration, camera access, diffuser use, and privacy.
How does LUX Meter measure light?
It reads the exposure your iPhone camera chooses for the scene, including ISO, shutter speed, and aperture, then converts that into an illuminance estimate in lux. iOS does not give apps a raw ambient-light sensor value, so LUX Meter uses the camera.
How accurate is it?
Treat readings as estimates, not lab measurements. LUX Meter is best for comparing spots and checking whether a space is dim, comfortable, or bright. Calibrating once against a trusted meter can make readings closer on your specific device. For regulated, safety-critical, or compliance work, use a certified lux meter.
How do I calibrate it?
Tap the calibration row under the reading. Point your iPhone at a spot with a known lux value, ideally measured with a trusted meter, enter that value, and apply calibration. LUX Meter stores a correction factor locally on your device. You can reset to default at any time.
What is the diffuser tip about?
Incident-light readings work better with a diffuser over the lens. A simple option is matte white printer paper over the camera. For best results, calibrate again after adding the diffuser so the app accounts for your setup.
Lux or foot-candles?
Use lux for the metric standard. Use foot-candles for lighting and photography contexts where that unit is preferred. 1 foot-candle equals 10.764 lux.
Why does the app need camera access?
The camera is used as the light sensor. LUX Meter only reads brightness from the live camera feed. No photos or videos are taken, stored, uploaded, or shared. If you decline access, enable it later in iOS Settings under LUX Meter.
It says the camera is unavailable.
This usually happens when the app is opened through iPhone Mirroring on a Mac because iOS blocks the iPhone camera in that mode. Open LUX Meter directly on the iPhone and metering will work. The iOS Simulator also cannot measure light because it has no real camera feed.
Does it work offline?
Yes. LUX Meter works on-device. It has no accounts, no ads, no tracking, and no cloud sync. Measurements stay on your device.
What do Hold, Reset, and Min/Avg/Max do?
Hold freezes the current reading. Reset clears the session statistics. Min, average, and max track readings since the last reset, which helps when comparing different spots in the same room.