Red and near infrared light are thought to act primarily on the mitochondria of cells, leading to greater energy (ATP) production. Any cell that has mitochondria will, in theory, see some benefit from appropriate light therapy.
Various wavelengths are shown to be effective, including 630nm, 685nm, 810nm, 830nm, etc. Several studies compare lasers to LEDs, which show equal (and in some cases superior) results for oral health. LEDs are much cheaper, being affordable for at-home use.