Thanks Brian! Re the crop, I'd come to the same conclusion after I posted it on Instagram which cropped it square... it works well.
On the original colour image (from my D750) that bright spot is green and clearly a reflection off something... maybe a car? I didn't really notice it at the time.
Now, I must confess that there was a little trickery involved in this image!

Both shadows are myself... standing in the same spot too, but lit by two different streetlights. I just took two photos with my spare arm in different positions and layered them together in GIMP. BTW the grain isn't added - just the result of ISO 12800 and a lot of added contrast.