Light therapy has been shown to have significant biological effects on humans. For example, light therapy is used to manage depression. Several clinical trials have shown that certain wavelengths of light can improve wound healing, decrease temporomandibular joint dysfunction (TMJ) pain, and decrease fear of back pain. In these trials, light was directed at the site of pain. In an attempt to better understand the effect of different wavelengths of light, pre-clinical studies were conducted using rats. The investigators have shown green and blue Light emitting diode, (LED) light produced antinociception (analgesia) and reversed neuropathic pain associated with several models of chronic pain. The analgesic effect of light was completely blocked when rats had their eyes covered, this suggests that the analgesic effects seen are mainly due to systemic effect through the visual system.