Anxiolytic Effects of Green Light
In humans and mice, green light therapy relieves anxiety
Summary
When Harvard researchers compared patients undergoing talk therapy in a green light setting versus white light, they observed the patients in green reported significant improvement in symptoms of general anxiety disorder. Green-light sessions raised positive and lowered negative feelings significantly more than white light, but researchers don't know how.
Similar findings have been reported in dentist offices using green decorations and among children with access to green spaces.
A new study of mice showed a similar improvement in anxiety related to green light, and this time the scientists think they identified a mechanism in the brain related to glutamate signaling.
The Comforting Effect of Green Light
General Anxiety Disorder (GAD) is one of the most common mental disorders for which adults seek psychotherapy, even though most traditional talk therapy approaches are notoriously ineffective. According to a recent review, only cognitive behavioral therapy (CBT) demonstrated lasting improvement in self-reported symptoms of anxiety (Papola et al 2024).
However, the migraine headache research group at Harvard has an idea. They noticed that their green light experiments did more than relieve migraine headache pain -- the exposure to green light also helped reduce patient anxiety. Their headaches patients said that exposure to other colors not only increased pain, but it made them feel anxious, with tight chests, racing hearts and shortness of breath. Under the green light they felt calm.
To test whether the green light was operating on the anxiety independently of pain relief, they asked 13 GAD patients to undergo a comparative trial by replacing their ordinary office lighting with narrowband LED 520nm green light during their therapy sessions.
It worked.
Patients reported significant improvement in self-reported symptoms of anxiety resulting from their green light sessions, compared to the ordinary white lighting (Melo-Carrillo et al. 2023).
The Harvard results are consistent with other studies that show green light in office settings has a positive effect on mood. For example, when twelve autistic children aged 6 to 17 each had a teeth cleaning in a standard white-light room they exhibited more stereotypical uncooperative behaviors than when they experienced the same cleaning three months later in a green-light room (Sawicki et al. 2024). Adults wearing green sunglasses during painful dental procedures exhibited significantly reduced stress and pain without any adverse effects (Takemura et al. 2021) and young children who lived near residential green spaces showed lower rates of anxiety and depression, even after adjusting the data for family and neighborhood factors (Towe-Goodman et al. 2024).
This collection of small studies, and others related to them, indicate that green light exposure is doing something good for mood and mental health -- it's just that none of the human studies so far can explain how.
Mice Experience Relief from Anxiety Under Green Light
The human brain is so complex that it does not give up its secrets easily. Consequently, researcher often resort to animal models to identify the pathways and mechanisms by which environmental exposures might act inside the brain.
The problem is that mice don't experience the anxiety of missing a rent payment, having a big exam tomorrow, or worrying about a romantic break up. Nor can they mark self-reported Likert scales that record mood. To study anxiety in mice, scientists must first induce it, then decide on how they might observe and treat it.
That's exactly what a research group in Hefei China decided to do. First, they stressed experimental mice in two ways: 1) restraining their movement by confining them to tubes, and (acute restraint stress, ARS) 2) placing them on a hot plate. Then, too see whether these stresses created anxiety they observed the extent to which these experimental mice were willing to explore (open field test, OFT), and how well they navigate a maze (EPM). Finally, they let the poor mice wander freely between two environments, one lit by white light and one by green -- just to see if they exhibited a preference.
The mice exposed to a green 515nm LED strip performed better than those that did not get green light exposure. The researchers concluded that the green exposure had relieved anxiety in acute stress model mice. Moreover, when given the freedom to choose, the only the stressed mice showed a significant preference for the green LED space (Zhang et al. 2026).
How Does Green Light Do It?
The next challenge for the Chinese team was to identify a mechanism within the brain. They zeroed in on something called glutamatergic neurons, which they were able to as the neural circuit mediating the anxiolytic effects of green light in the acute stress model mice. These are neurons that use glutamate, the brain's main excitatory neurotransmitter, to signal.
Glutamate and gamma-aminobutyric acid (GABA) act as opposing signals in the brain. Glutamatergic neurons release glutamate, which excites neurons. GABAergic neurons release GABA, which inhibits them. Psychiatrists treating patients with anxiety will sometimes prescribe drugs that act on GABA receptors, like benzodiazepines such as alprazolam and lorazepam, to boost GABA's effect.
Rather than acting on the GABA system like benzos do, the mouse study concluded that green light inhibited the glutamate signalling systems in the stressed-treated mice. Pharmacological blockade of the green light pathway abolished the beneficial effect.
They wrote:
Biologically, wavelength selectivity in light-modulated emotional regulation is thought to arise primarily through spectral tuning and circuit specificity of retinal photoreceptors and retinal ganglion cell (RGC) subtypes. Different RGC classes, including melanopsin-expressing intrinsically photosensitive RGCs (ipRGCs) and cone-driven conventional RGCs, encode distinct spectral and irradiance properties of environmental light and relay this information to discrete brain targets through parallel visual and non-visual pathways. A growing body of literature has demonstrated that these circuits regulate diverse physiological and behavioral processes, such as mood, anxiety, memory, sleep, metabolism, immune responses, and nociception. - Zhang et al. (2026)
The Eyes Signal the Brain
In other words, when eyes sense the light environment, they send signal to the brain via the glutamate signaling pathways that either say "This dangerous," or "This is safe." White and blue light leave the possibility of danger open, exciting the glutamatergic neurons, whereas when all other wavelengths are removed from the visible spectrum and only green remains, the glutamate signal turns down, allowing GABA to take over and rescuing the subject from their catastrophizing mind.
Green Inhibits Shiver Response?
My connection to both MyGreen and Morozko Forge has motivated people to experiment with doing their ice baths while using MyGreen Lamp to shine on their closed eyes. Every subject who has tested this protocol so far says that the green helps calm them down and suppresses their urge to shiver.
This new mouse study helps inspire a new hypothesis as to how the green light affects the ice bath experience. We already know that thermal receptors in the skin activate glutamate signaling during the gasp reflex. That is, glutamate signaling is required for cold defense (Nakamura and Morrison 2008). Since we now know that green light exposure thru the eyes will inhibit glutamate signaling, we have to wonder whether the green light modification of glutamate signalling in the brain reduces the anxiety of the ice bath, if not the sensation.
References
Nakamura and Morrison, Nat Neurosci 2008, doi:10.1038/nn2027; Yahiro et al., J Neurosci 2023, doi:10.1523/JNEUROSCI.0643-23.2023)
Papola D, Miguel C, Mazzaglia M, Franco P, Tedeschi F, Romero SA, et al. Psychotherapies for generalized anxiety disorder in adults: a systematic review and network meta-analysis of randomized clinical trials. JAMA Psychiatry. 2024;81(3):250-. doi:10.1001/jamapsychiatry.2023.3971.
Sawicki CM, Duran P, Hestehave S, Khanna R, Wade SD. Green light exposure in children with autism spectrum disorder: a pilot study. J Clin Pediatr Dent. 2024;48(4):99-107. doi:10.22514/jocpd.2024.083.
Takemura Y, Kido K, Kawana H, Yamamoto T, Sanuki T, Mukai Y. Effects of green color exposure on stress, anxiety, and pain during peripheral intravenous cannulation in dental patients requiring sedation. Int J Environ Res Public Health. 2021;18(11):5939. doi:10.3390/ijerph18115939
Towe-Goodman N, McArthur KL, Willoughby M, Swingler MM, Wychgram C, Just AC, et al. Green space and internalizing or externalizing symptoms among children. JAMA Netw Open. 2024;7(4):e245742. doi:10.1001/jamanetworkopen.2024.5742
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