The adjustable lux means this sensor switch can be used to auto switch off lighting when there is sufficient daylight.  For example, the sensor can be set to keep lights on during cloudy or overcast conditions, but if the sun comes out with full daylighting, then the lights can auto turn off saving electricity. At the end of the day, the manual light switch can be turned off cutting power to this sensor to ensure lights do not stay on overnight, or alternatively, the lights can be fully automated using one of our timer switches.