I can't speak to red light therapy except to say it seems to be provided mostly by chiropractors. The few I know who have tried it have had mixed reviews. I know there are different wave lengths so maybe that is the difference. The idea is that the light and heat penetrate deeper than other methods.
I believe the reason you don't get much of an answer to the question about different causes is because the treatments aren't that different. One exception is the treatment of the underlying root cause.

The suite of medications they pick from is the same, but really is just to mask the pain, they do nothing in the way of repair or regrowth. That has to come from (if it is possible for your nerves) good nutrition, stimulation, and oxygen. these are the three things nerves need to be thier healthiest.