READ THIS PLEASE..... You can also try cleaning the area gently with a damp cloth. Just make sure everything is off.
Up until recently I have never plugged my charger port in upside down. Today upon doing so, in about a minute it went very dim. I played around a bit and noticed that if it's adjusted you can achieve a normal green light. Hope I helped someone!
Specs............
Mid 2012 MacBook Pro / "L" type "Magsafe Charger"