According to many reports brewing across the Internet, the Nokia Lumia 630 and 635 does not come with a built in proximity or ambient light sensor, but that is not true.
Nokia has itself confirmed that both Lumia windows phones come with proximity sensor as well as ambient light one. Proximity senses objects in front of screen while ambient one controls the brightness of the display. Here is the screenshot that shows that it has both.
The only difference 630 and 635 is that former comes with a dual SIM slot while 635 features single SIM. Other than that there are no differences.