Red light therapy (also known as photobiomodulation (PBM), involves exposing the body to therapeutic levels of red and/or near-infrared light through specially-designed LEDs. This light penetrates the skin and stimulates circulation, while also being absorbed by mitochondria in cells activating cellular energy production, which can promote healing, reduce inflammation, improve skin health, It's how scientists and researchers took the high level intensity of laser light therapy and created a way to deliver it effectively in a more gentle, accessible way.
Red light (660nm) gets all of the credit because it's in the name of the therapy. But it primarily benefits the skin and creates micro circulation increase, stimulating collagen and elastin production. Near infrared (850nm) is really doing a lot of the other work because it goes more deep into the body and reaches the mitochondria in cells and tissue beyond the skin. Both lights have targeted and systemic effect.