Backlight goes dim when typing

Hi I have recently changed the LCD screen on a iPhone 6 exactly the same as I have done in the past .

The problem I am having is that sometimes when touching the screen or typing a message etc the screen goes very dim and then comes back brighter when not touching the screen .

I have checked all connectors and everything looks fine and the phone has been fine for 2 weeks and has just started doing this .

Could it be a faulty LCD but I would have thought it would do it all the time not just when pressing on the screen .

Any help much appreciated

I purchased the screen with the proximity sensor , camera, home button etc and everything looks fine . It has worked fine fir about 2 weeks but the screen goes dim just when typing or pressing on the screen . Other than that the phone works fine .

I wish I still had the old screen to try but I have thrown it away as that one never did that but at least it would prove it was the screen and I can send it back