What an Ambient Light Sensor can do?
Close Active Apps
99% apps are running in the background of your smartphone which can drain your batter almost to nil. So it is always recommended to close active apps which are not used currently.
Turn off Wireless connectivity
Turn off mobile data, WiFi, GPS when not needed or not in use. Turning off 3G can save a lot of battery.
What will happen if I turn on WiFi?
If your WiFi is switched on and your not in the WiFi range, the smartphone will always keep looking for WiFi hotspot to get connected, which will use a lot of battery.
Power-saving modes
Turn on power saving mode which provided by smartphone manufactures. Eg. available in Samsung devices.