How much lower back bruising should there be following open lumbar laminectomy l 3 thru l5?

From none to alot: This is dependent on the amount of bleeding and use of a post op wound drain as well as your use of any aspirin, fish oil or other medication that may affect bleeding and when or if you stopped them preop as well as any use of blood thinners post op to minimize any blood clots. It may also be that you could have some type of bleeding history as well. In any case, it should not affect outcome.

Very common: Laminectomies require a good deal of dissection which results in post-ooperative pain and some bleeding. The bruising you're experiencing is the result of some of the inevitable bleeding that occurred. If the wound were to become hot, progressively inflamed, began draining anything that looked like puss or you began experiencing a fever you should consult your doctor.