Im pretty sure that the luk, your window displays, is not the true luck at all. The correct formular for the true luck is:
1 + LUK x 0.3 + Crit cards
Means 3 points in luck, get you 1.9 crit
Oh btw, someone mentioned the Crit penalty, if i remember correctly, your chance to crit, will be reduced by Target luck/5, but i can be wrong on this one.