In February 2017, researchers showed that rats exposed to green light appeared to feel less pain than ones in white light (see reference below). At a meeting in November 2017, they presented results of a small study (not yet published) showing the same effect in humans with migraine or fibromyalgia. To acheive the pain reduction, people spent 1-2 hours a day in a room with only green light from LEDs.
The original research showed that rats kept in green light, or fitted with green contact lenses, reacted less when made to feel pain.
Follow-up research in humans has shown the same effect. It was presented at the annual meeting of the Society for Neuroscience in Washington, DC, USA, November 2017. This is reported in the RELIEF newsletter of March 2018 (scroll down to the item titled 'Update: Green light is a go in people'). Quote from this site:
At the meeting, the researchers reported that humans with either migraine or fibromyalgia lowered their pain rating from about an average of seven (out of ten) before treatment with green light to about a three after light exposure. Subjects used the lights daily for ten weeks, with benefits emerging after about three weeks.
"They showed about a 60 to 70 percent improvement," Ibrahim said of these patients.
The patients were exposed to green light from a light-emitting diode (LED) strip—similar to those used for party and kitchen lighting—for an hour to two hours each evening at their home. Control subjects received white light strips to use at home. Each week, the study participants filled out five different surveys to report their pain, quality of life and daily activity, which revealed the beneficial effect of green light.
"You need to be in a dark room with no light pollution, no screens," Ibrahim said. "But as long as your eyes are open, you can read, meditate, or just relax."
The researcher commented: "Self-treating with green light is probably premature, but this is not invasive, and there is no risk."
Reference: Pain. 2017 Feb; 158 (2): Pages 347-360. Long-lasting antinociceptive effects of green light in acute and chronic pain in rats. Ibrahim MM, Patwardhan A, Gilbraith KB, Moutal A, Yang X, Chew LA, Largent-Milnes T, Malan PT, Vanderah TW, Porreca F, Khanna R