I'm pretty sure the L stands for "Lyhyt", which means short. At many events there is an a "A" and an "AL" class. They just have an "A" class because in some really big ones they might also have a "B", "C", "Elite" etc.
I don't believe the L classes are significantly less difficult, they're just shorter.
But, here's the routegadget for last week's Finnspring, where all the categories had an L class, even H21, so you can judge for yourself -
http://routegadget.tulospalvelu.fi/2014/cgi-bin/re...