What is this with gear

I bought with 700 souls gear and can't get lighting shoulders , maybe because I am low lvl and I am in low tear now help please

I am now at stage (1-9) dark difficulty I didn't get yet any weapon or shoulder tier 16 (unique grade) what is the possibility to get them from dark difficulty or i should back yo play at inferno difficulty to get them ? Thanks xD

Go's by every 4 lvl I'm still in lvl 2 gear at lvl10