I have commuted with a Specialized Rock Hopper for several years.
Lights: I prefer a helmet mounted light because I want people to see me so I stare at them before they think about pulling in front of me so the light hits them in the face and then I move my head back and forth so it flashes.

Numbness: usually due to pressure on the median nerve in teh wrist due to carpal tunnel. Best option is to see if you are cocking your wrists while you are riding. To avoid it, concentrate on keeping your wrist straight.