LightSaver allows very fine control of your Display's Brightness (and hence, your Battery Use) while you are running any App. LightSaver is normally accessed thru the Notification Bar or thru the Task Manager and is only a few presses away from all Apps.
Normal Phone Use
A large part of Phone Use is in answering and making calls (it is a phone after all). Full brightness is not normally needed in this case. Most users can answer and make calls with the brightness setting set as low as 30%.
Checking the time and date and perhaps, the battery level on your phone can also be done at a low level unless your are outdoors in bright sunlight.
Heavy Display Use
Of course, your smart phone will be used for serious browsing and gaming and that means a brighter display is needed. Unless you have to do this in the open in bright sunlight, you can set the brightness down to 70% and still not miss anything.
If you find yourself in a dim room then you can set your display to as low as 50% and still be comfortable. The best situation is a totally dark room where setting the brightness to 30% or less can still let you browse or play - with the added bonus of not disturbing anybody (like in a movie or bedroom).
Benefits of Brightness Control