Like egg that much huh? 
OK, I tested with my 2330L with 1.12 F/W... put in room with no other IR... IR Light Control on Low/High - I saw a difference in image.
But OFF is OFF.. with 1.14 F/W - there is the leakage with "OFF".
My 5222LB - older F/W --> Firmware Version : 2.01
I turned IR light control lower, and the IR's dimmed compared to HIGH...
I had always accepted dlink default (medium)... as it generally worked fine everywhere...