Your Android will be light meter.
This is a photographic exposure meter.
You can use the illuminance sensors of smart phones, to know the f-number and shutter speed easily.
Step of the shutter speed is ed on continental series and multiple series.
!!NOTICE!!
Measurement results of the exposure meter is dependent on the accuracy of the included light sensor on Your SmartPhone.
If so, you can ajdust manually result value (0.25EV step).