I have constrained my bones after having finally restrained them. It was probably the coffee. But speaking about bones, here is what I accomplished in Blender:
I set my LowerArm bone to X- Min. -80, Max. -10. Seemed good enough t me.
But I also played around with my overall lamp shape. I found the base a little taller than my liking, the rotating piece holder a little to large, and the two arms too small.
Outside of that my stem was doing some strange things when I went to local. But once I had reset the rotation in pose position, it worked itself out. I also noticed that when the top was rotating up and down, the rotating wheel was rotating on and off center. So I had to play a little with origins and centering my pieces. It would not have been noticeable zoomed out, but I found it bothersome.