This app uses the light sensor to measure illuminance in lumens per square meter (lx) or lumens per square foot (foot candles). FOR INDICATION ONLY. Results depend on your device and its hardware (Not every device has a light sensor and quality of the sensors varies massively). Features include:

Analogue dial to show current reading.
Averaging.
Maximum and minimum values.
lx or ft-c units.
4 time constant options. 3 Refresh speeds.
Graph – Shows the time depedence of the light.
Autoscale or manual (pinch & pan) Y-Axis.
Calibrate option – If you have a calibrated light meter or known light source, you can use this option to calibrate the meter. (However app is still for Indication Only).

More details can be found on the website.