This is for those who enjoy the attention that Apple gives to details.
For many years, as you all know, computers in general on Macs have offered an energy saving function, which turns off the screen and / or puts the machine to sleep (sleep) after a certain period predetermined by the user. In the case of laptops, it is even possible to determine different periods for when you are plugged in or using the battery.
So far, nothing very special. But the OS X Mavericks improved this issue a little, as he discovered the The Verge it's the MacMagazine confirmed with own tests.
For some years now, Macs have been equipped with a light sensor which serves basically two things: automatically reduce / increase the brightness of the screen according to the intensity of the ambient lighting and, in the case of Macs with backlit keyboards, turn them on automatically when necessary.
Now, at Mavericks, this same sensor is also used to ?observe? if the user is still facing the Mac even without touching the mouse / trackpad or keyboard. Thus, if the person has stopped working on the machine because he is talking on the phone, for example, the sensor observes movements due to the variation of light captured and keeps the screen on for longer.