Contrast: difference between light and dark. You don't have enough.
Luminosity: amount of "glow" I think. He means that this is all-round a bit too bright.
I have one thing to add: you really, really need a contrast colour somewhere on this. It looks far too plain. Perhaps bring back the wires but do them all flowing in the same direction. Also, you can make them look better than they did before by highlighting the middle and darkening the edges.