I just compared my phone (Pixel 3a) to my Uceri meter, using the app that you link to here.
It seems okayish. The main issue with it is that the camera has a limited field of view, so it does not capture light coming from every direction. With the lux meter and the phone both pointed directly at the lamp near my desk, the phone reads about 35% higher than the lux meter, and when they’re both pointed at an angle that barely excludes the lamp from the field of view, the phone reads 45% lower than the lux meter. The reading on the lux meter only changed by 4% between these two angles.
I’d say if you’re okay with getting within a factor of two, the phone app is fine. The phone and the lux meter seem to agree the best when the lamp is just barely inside the field of view of the camera.
I just compared my phone (Pixel 3a) to my Uceri meter, using the app that you link to here.
It seems okayish. The main issue with it is that the camera has a limited field of view, so it does not capture light coming from every direction. With the lux meter and the phone both pointed directly at the lamp near my desk, the phone reads about 35% higher than the lux meter, and when they’re both pointed at an angle that barely excludes the lamp from the field of view, the phone reads 45% lower than the lux meter. The reading on the lux meter only changed by 4% between these two angles.
I’d say if you’re okay with getting within a factor of two, the phone app is fine. The phone and the lux meter seem to agree the best when the lamp is just barely inside the field of view of the camera.