The first lightcycle is concept art for the 2nd Generation lightcycle that Kevin Flynn created for personal use in 1989 (simplified version: One of the lightcycles in TRON Legacy). The second lightcycle is the original 1st Generation lightcycle that was standard issue in 1982 (aka: The one from the original TRON).
The two cycles do seem to have the same overall design, though, except for the fact that the 2nd Gen one is white and has some random exhaust vents scattered around it in a very cool Syd Mead-esque fashion.