When replacing iPhone LCD & Screen ,if you see an area that is brighter than other area .and this area just happens to be nearby the earpiece , camera ,or sensors with screws .most of time you would think ,I got a faulty one from Sintron iPhone Screen .Well...please hold on a second....

the reason is also possible that when you reinstall the earpiece , camera or screws .you didn't put them back correctly (or wrong screws problem ).so there's something behind that area is Pushing the Backlight of the Screen .then the situation would be similar to the picture shown below.

iPhone 6 Screen replacement

in this case ,please try to remove the possible parts such as earpiece ,camera ,home button etc...and test again to see if it works now.