The LED light doesn't go as deep and is not as strong as the Low Level Laser {better and goes deeper into tissues}.
Basically these certain light waves will affect the cells and helps them to release toxins, uptake oxygen and good stuff and helps in the healing process as well as helps with triggerpoints.

here's some websites that explain it better, they might have updated them- I've had theses links for yrs now -
Laser/ Infrared/ far infrared
http://laser.nu/
http://www.purehealthsystems.com/infrared.html
http://www.purehealthsystems.com/mus...in-relief.html
http://www.toolsforwellness.com/far-infrared.html

this site has info on ultrasound and triggerpoints -
http://www.drlowe.com./myofascial/pr...ltrasound1.htm

Do you think you have triggerpoints or have the PT persons mentioned it at all?
The muscles can't fully release/relax as long as there are triggerpoints.
there's more triggerpoint info in our useful sticky 1st post.