As far as I can comprehend from WP[0] "lay judges" have a more direct role in trials, where juries are mainly observers and merely make a decision based on the trial (including any instruction the judge gives them on evidence, assumptions, etc.). Interesting system, but I'm not really in a position to say which would be more effective (if either).

[0] http://en.wikipedia.org/wiki/Lay_judges_in_Japan