What was tested
ISO 2720
Formulas checked against published constants: ISO 2720 calibration constants and APEX.
500
Simulated camera streams with flicker, noise and auto exposure changes, used to test the reading logic.
1,735
Public iPhone photos behind the per-model corrections. Apple exposes about 0.4 EV darker than a classic meter, 0.1 to 0.8 EV depending on the model.
pvlib
The Sun check model is within 10% of the pvlib reference.
What published studies found
Phone light meter apps differ from each other.
8% to over 100%
Error without calibration.
About 8 to 10%
Error after a one-point calibration.
Vujica Herzog et al. 2022
Repeatability on a real iPhone
| Method | Scene | Readings | Spread |
|---|---|---|---|
| Quick | Bedroom at night, about 2 to 9 lux | 10 camera starts: 4 settled within 3 s, in about 2 s | 2.5 to 6.1 lux across starts |
| Quick | Same room, 60 s without moving | Below range on 61% of frames | Too dark for a firm number, so it says so |
| Flat and Card | Daylight room | Not tested yet | Added here after the test |
Want closer numbers?
Calibrate once against a meter you trust, and calibrate the paper you use.
How to calibrate