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Those are LED backlit, so it's more likely that it's the LCD than anything else, but it could still be the backlight board, any of the cables, or the logic board.
 
I had my keyboard backlight fail in my 2009 15" MBP after the first 3 months of use. AppleCare fixed it under warranty. The repair was listed as a "top case replacement" which I think is the entire aluminum shell around the keyboard.
 
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