All of surface pro 4s has this problem. I tried 2 and both has this issue...perhaps,this is normal!!i5/256/8 (model# 1724) lot #1544
From Day 1: Light bleed along bottom of screen when background is black with brightness turned up in a dark room.
The photo below demonstrates problem with Brightness at full against a black background in an unlit room at night. I plan to return the Surface for another unit once I'm convinced that the odds are in my favour of getting a good unit rather than another bad.
See photo of issue here:
( ExampleLightBleedSP4i58GB.jpg )
All of surface pro 4s has this problem. I tried 2 and both has this issue...perhaps,this is normal!!