While logging in initially the screen doesn't show problems but soon as time moves after some minutes horizontal lines start appearing in the bottom of screen of black or multi colored that progresses till the entire area corresponding to the app dock is obfuscated... So when I shut down at this time and reopen it.. Some lines still remain and it increase like earlier and results in same... Only when I shut down for a long time.. The screen becomes normal after logging in.. But still after some minutes same issue is reproduced... Using Screenshot and analyzing the picture shows that the defect is not reproducible in Screenshot and is visible in direct display only.. Please advice
The LCD is failing, sounds like. You've essentially already proved this by taking a screenshot that does not display the issue you are seeing (the artifacts). This happened on my SO's 2013 MacBook Air. I believe it's a fairly common issue, sorry to say.