There is good evidence that red-light therapy, at least when used with a professional-strength machine in a physician's office, is useful for various purposes in dermatology. There is some evidence that it is useful for various purposes in ophthalmology, especially in children and adolescents, and for management of pain from certain sources. (Citations on request.) There is no evidence that it is useful for treating any ailments discussed in this forum. Anyone who disagrees, feel free to correct me with a citation to a peer-reviewed study in a reputable journal.

Why a peer-reviewed study in a reputable journal? Because lots of "wellness" companies hawk their products either with "studies" that they conducted themselves - I wonder what they found? - or even just by "testimonials" from users who (a) are unfamiliar with the placebo effect or (2) may not even exist. Moreover, there are plenty of non-peer-reviewed "journals" that exist just to provide a place to publish stuff, frequently for a fee. Hence the gold standard: peer-reviewed, double-blind, placebo-controlled studies. Accept nothing less.