I was replacing a MacBook Air 2011 13” and created a short while installing the backlight cable. I experience the same thing shadow on bottom half the screen. I looked careful at the led strip, and I noticed some led’s did not light, creating this shadow effect. I looked at some spare lcd cover with the backlight in it under a magnifier, and it seems it can be replaced by unsoldering each bad led, on my case it was like 5 of them. I’ll try to get some pictures to get an idea on how to fix it.