Our "light whisperer," Randall Whitehead, IALD, explains where to place a bedside swing-arm sconce.
What is the normal height to mount a swing-arm lamp if it is to be used for reading next to a bed?
Of course, there is no simple answer to this question. The optimum location for the swing arm lamp is between your head and your book (or Kindle or laptop). Then the height of the bed and the slouchiness of the reader are also factored in.
I tend to like the swing-arm lamps that not only adjust from east to west but also from north to south. This gives you the most flexibility and allows a couple to mount their reading lamps at matching heights even if their reading positions differ. I actually make the client get into bed to measure the correct height. I am the “light whisperer.”