Reading medical journal articles is like doing battle with a big dictionary. Lots of polysyllabic words, and lots of abbreviations.
Photobiomodulation, shortened to PBM, is defined as the use of low level red and near-infrared light on the body. The intention is not to heat or burn the tissues, but to give a bigger dose than you would get from just sitting in the sunshine.
PBM is also called LLLT (low level light/laser therapy). The very earliest experiments used laser lights, but it has now been realised that LED lights are just as good, and in some ways, better than lasers. Laser light is coherent, meaning that it is in a highly concentrated beam and doesn’t scatter. This is fine if you know exactly where to point it. LED lights are non-coherent, meaning that they happily scatter. When you don’t have a specific target then this is the best approach. As well, there is good evidence that the more that the head is bathed in red/infrared light, the deeper the penetration of the light. So LED lights are increasingly selected for PBM research – it helps that they are cheaper and easier to use.
Red and near-infrared light works in two ways – the direct effect and the indirect effect. In some articles, the term “systemic” is used instead of “indirect”. For those who use Eliza light hats, the indirect or systemic effect is working hard, but there is some direct effect as some of the light will penetrate into the top of the brain tissue.
I’m attaching an article January 2017 called Photobiomodulation and the brain: a new paradigm by Madison Hennessy and Michael Hamblin.
It covers the new research areas in PBM, and gives some interesting summaries of the findings to date.