I have compared a professional luxmeter with the free app “GPS Status” which also displays a Lux value. The readings were within 30% tolerance for normal lighting situations. A smartphones light sensor will clip at some (high) value though. This clipping value can easilly be tested by pointing the sensor directly towards the sun.
It might well depend on the smartphone model. My tests were done with an older Motorola and a Oneplus 6. I’d guess a free app will be sufficient for most purposes.
I have compared a professional luxmeter with the free app “GPS Status” which also displays a Lux value. The readings were within 30% tolerance for normal lighting situations. A smartphones light sensor will clip at some (high) value though. This clipping value can easilly be tested by pointing the sensor directly towards the sun.
It might well depend on the smartphone model. My tests were done with an older Motorola and a Oneplus 6. I’d guess a free app will be sufficient for most purposes.