Nokia does not include some of the sensors in the device, as it appears that he does not have the proximity and ambient light sensors. The first is used to detect objects close to - for example your face, so it can lock the screen during a call. The latter is used for automatic display brightness control.
As a comparison, the predecessor of the Nokia Lumia 630, the Lumia 620, comes with an ambient light sensor, an accelerometer, a magnetometer, and a proximity sensor, whereas the 630 features only an accelerometer. Even the very affordable Nokia Lumia 520, which is among the most successful devices the Finnish manufacturer has ever released, also comes with proximity and ambient light sensors.
Undoubtedly, the lack of these has allowed Nokia to cut down a dollar here and there, but how has the company succeeded in emulating the functionalists of the proximity sensor? Well, it seems that the capacitive touchscreen switches the display off when it detects a large object in its upper part, preventing users from, say, hanging up a call with with their cheeks or ears. Usually, a proximity sensor takes care of this feature, but its absence in the Lumia 630 has apparently forced Nokia to think of this different method.
