Question
I have a friend who has heard something about
Laser Light used by Chriopractor.  What does a Laser Light do to relieve pain?

Answer
If you mean Cold laser or Low-Level Laser Therapy:
Basically a very weak laser is introduced to the damaged / painful area and it seems to stimulate cell growth and regeneration of the tissue. So it may indirectly decrease pain by speeding up recovery time. The more complex the injury, the more treatments required. Treatments can last seconds to minutes and you need 4-6 to notice any difference. Here is a web site of a Low-Level Laser Therapy machine provider if you want more info, http://www.meditech-bioflex.com/

I have no personal experience with this therapy. It does have some research to back it up, though it is still a newer treatment. As far as I am aware it's uses are still being investigated.