In the interests of providing the reason for my use of low intensity light therapy I'm quoting extensively from the relevant chapter of The Brain's Way of Healing by Norman Doidge, M.D. New York; Penguin(Viking), 2015. Chapter 4, "Rewiring a brain with light". This book is worth reading in its entirety, the chapter on light treatment was the most relevant to my condition.
"In the immune system, laser light can trigger helpful forms of inflammation - but only where required. Where inflammatory processes have become stuck and "chronic" as happens with many diseases, laser light can unblock the stalled process and quickly move it to a normal resolution, leading to decreased inflammation, swelling, and pain.
"So many modern diseases, including ... all the autoimmune diseases (such as rheumatoid arthritis and lupus), occur in part because our body's immune systems produce excess chronic inflammation. In chronic inflammation, the immune system stays on too long and may even begin to attack the body's own tissues, as though they were outside invaders. The causes of chronic inflammation are many, including diet and, of course, the countless chemical toxins that become embedded in the body. Chronically inflamed bodies produce chemicals, called pro-inflammatory cytokines, which contribute to pain and inflammation.
"Fortunately laser light fights excess inflammation by increasing the anti-inflammatory cytokines that bring chronic inflammation to an end. They lower the number of "neutrophil" cells that can contribute to chronic inflammation and they increase the number of "macrophage" cells in the immune system, the garbage collectors that remove foreign invaders and damaged cells." pp. 141-2
"Dr. Shimon Rochkind...has shown that applying low-intensity lasers to peripheral nerves can help them heal, and that the light improves nerve-cell metabolism, increases sprouting of new connections between nerves, enhances the growth of new nerve axons (which conduct electrical signals) and of myelin (the fatty covering around the nerves that allows them to send faster signals), and decreases scar tissue". p. 151
(Just to clarify, the laser treatment involved is NOT from those little LED gizmos you can buy many places. The company does now sell a unit for home use and that is several thousand dollars. The treatments last for a significant length of time - in my case usually about 40 minutes a session, although I understand other conditions require longer. I started with a few weekly sessions, graduated to twice weekly, then attempted to reduce to weekly, then fortnightly. I had to go back to weekly sessions again for a few visits, and am now trying fortnightly again. When I was attempting to reduce from 4 to 3.5 I seemed to hit a roadblock, but suddenly it's as though the road suddenly cleared.)
And here is a link to an English clinic where treating PMR with low intensity light is actually discussed (there have been as far as I know no clinical trials for this therapy, so positive results are anecdotal, like mine):