It’s that time of the year again! The winter blues, photobiomodulation and hype marketing.

Maya Chanturishvili MD

I have always been a morning person, and during the height of summer, I am typically wide awake at 5:30 AM and energetically at work by 7:30 AM. I do that not to impress my direct supervisor (who would never be impressed anyway), but out of biology. I can no longer replicate my sleeping habits when I was a teenager waking up at noon or later. At this age, the moment those first photons of sunlight stream through the window I am wide awake and no matter how much time I try to get a few more minutes of sleep, I just end up getting a headache. Things change come September. By that month I need my alarm clock to wake up, and by the time Daylight Saving Time ends, I am fatigued and tired by 4 PM (can someone please tell lawmakers to keep Daylight Saving Time permanent?). You could say in deep winter, maybe I do suffer a mild depressive episode now and then and prefer to sleep the entire day.

Oftentimes called “the winter blues,” in its’ severe form, Seasonal Affective Disorder recognized by DSM 5 as a type of Major Depressive Disorder1, can be as disabling as any mood disorder. Theories about what physiologically causes SAD abound, from decreased serotonin production, increased serotonin transport away from the central nervous system, increased melatonin production to decreased Vitamin D production. Regardless, all these potential causes, plus the fact that both winter blues and SAD is more frequent the farther you are from the equator, point toward the effects the sun has on our biology. I mention the sun because I don’t believe there can ever be a light source that can approximate the effects the sun, or the lack thereof, has on our bodies. After all, the sun has played a big role in our evolution and in our social construct of race. Sunlight as it reaches our bodies is way more complex than the light that comes out of your light bulb (or from your DUO arrays). It is white light (not just red or infrared) and the various components of white light from ultraviolet to near infrared that have different effects for biological systems. The conventional light therapy used for SAD is called bright light therapy. Unlike with photobiomodulation, wherein we tend to equate wavelength specific dosage with irradiance (w/cm2), recommendations for bright light therapy is cool white light (which also includes blue, yellow and green) at an illuminance (instead of irradiance) of 10,000 lux. The key here is brightness, rather than radiant energy delivered to our skin.

Anders, et al, suggested that PBMT be defined as “A form of light therapy that utilizes non-ionizing forms of light sources, including lasers, LEDs, and broadband light, in the visible and infrared spectrum. It is a nonthermal process involving endogenous chromophores eliciting photophysical (i.e., linear and nonlinear) and photochemical events at various biological scales. This process results in beneficial therapeutic outcomes including but not limited to the alleviation of pain or inflammation, immunomodulation, and promotion of wound healing and tissue regeneration” when PBMT was accepted as a MeSH term by the National Library of Medicine. Is bright light therapy therefore, a form of PBMT? If we judge it purely by the definition mentioned, it should be but not the other way around. Doing a literature search using Pubmed with search terms photobiomodulation and seasonal affective disorder does not show any hits. Further, if you use any search engine with the same terms, you will only end up with overhyped marketing efforts by private clinics on using whole body “red light therapy” to treat seasonal affective disorder. Bright light therapy, although by definition also PBMT, basically tries to emulate a person walking outside on a bright but cloudy day on Earth…not on Mars. A lot of the discoveries we know about PBMT have stemmed from the use of bright light therapy. The release of serotonin, melatonin and the production of Vitamin D are highly dependent on the effect of UVB, blue, yellow and green wavelengths on your eyesight and your skin. Would using pure red and near infrared light produce the same?

There are actually studies that potentially document improvement in mood for SAD using just near infrared light. There are also studies that document the potential for using near infrared light for non-seasonal depression. Near infrared light after all, can penetrate deeper through tissues and, if we use the laser probes, can potentially actually reach cerebral tissue. However, the precise mechanism by which NIR can affect depression is still unknown. As NIR is probably not detected by opsins in our retina (which is most responsive to blue), one would speculate that this is due to classic theory of how PBMT affects another light sensitive porphyrin, Cytochrome C Oxidase (CCO). We all know ad nauseum how PBMT theoretically works, by releasing NO from it’s binding with CCO and the subsequent increase in ATP production. We know of the cascade of reactions that follow, from NO causing vasodilation to the release of ROS which causes the subsequent release of certain molecules that affect everything from cell differentiation, cell multiplication and inflammation. However, we don’t know how this reaction affects mood disorders unlike our knowledge of how certain antidepressant medications inhibit neurotransmitter receptors. A lot of chemical reactions in our brains are secondary to our visual perception of light, so how could an invisible light source like near infrared, or even red, which is oftentimes not even perceived by most mammals and are used in zoos to light up nighttime displays for nocturnal animals, improve our mood? Some speculate that red and near infrared, which supposedly doesn’t influence melatonin production, can improve Non Rapid Eye Movement (NREM) sleep, which is a requirement for a well-functioning glymphatic system3 and might seem paradoxical since we are already sleepy during winter. It is also hypothesised that the effect of PBMT might also be mediated through the eyes by retinal cells that are not part of the visual system4. This interplay between near infrared light, NREM sleep and the glymphatic system and even improved cerebral circulation is still being investigated and it could be possible that more quality sleep (rather than just the preference to lie in bed and cry for hours in winter) is what is needed. For certain depressive symptoms secondary to an inflammatory condition (think traumatic brain injuries, post-stroke or multiple sclerosis), this improvement in the brains capability to mop up waste materials in your brain such as βAmyloid or Tau proteins may be responsible for the improved mood and the production of certain mood related neurotransmitters like serotonin and dopamine. Thus, some claim that bright light therapy (and by association, near infrared via PBMT) may improve mood not only for SAD but for non seasonal unipolar depression as well5 though effects that might be due to more than just our confused circadian rhythms. 

I’ve seen so much overhyped marketing campaigns featuring people either standing naked in front of two light panels (essentially walls) or inside coffins (ahem, ahem…beds) bathing in nothing but red light as treatment for SAD. I don’t know about you, but being kept in an enclosed space for a period of time with everything around me coloured red like I was in Dracula’s castle doesn’t really make me happy. What would make me happy in the midst of winter is walking in a bright greenhouse. So do I think red and near infrared has a place in the treatment of mood disorders? Yes I do. With guidance from psychiatrists or psychologists and making sure that other proven regimens like antidepressants or cognitive behavioural therapy are not just abruptly discontinued, I do think the addition of targeted PBMT (as opposed to whole body PBMT) using our time tested red and near infrared wavelengths as a supportive treatment (but not as an only treatment) for major depressive disorders should have its place in the arsenal against mood specific disorders. But specifically seasonal affective disorders? If the theory behind SAD bids true regarding melatonin, serotonin and Vitamin D production, then aside from red and near infrared, vision and skin exposure to other wavelengths should also be considered. Maybe you don’t need to sit in a room for an hour blasted with 1000 watts of white light but going out for some sunshine in the middle of winter (assuming you’re not in the middle of a snowstorm), changing your orange glow bulbs to warm white, cool white or daylight bulbs or giving yourself a respite from being told to hold off from looking at your cellphones during daytime might help. Some studies actually do not find a difference between the effects of bright light therapy and just near infrared6 as a treatment modality for SAD so why settle with just two wavelengths? I have an indoor grow tent blasting white light but including some UV and some infrared where I grow my tropical aroids, orchids and other epiphytes. My plants are not kept in purely red coffins (photosynthesis also requires blue light) and even if you can use those pink lights which has both red and blue wavelengths to grow your indoor marijuana plantations, nothing beats using white light to not only make your plants happy, but you as well. No wonder plant people are such happy people! It keeps you going all winter until longer daylengths (with natural white light, not perpetual sunsets) start signalling the arrival of spring and consequently, even better mood.



  2. Anders JJ, Lanzafame RJ, Arany PR. Low-level light/laser therapy versus photobiomodulation therapy. Photomed Laser Surg. 2015 Apr;33(4):183-4. doi: 10.1089/pho.2015.9848. PMID: 25844681; PMCID: PMC4390214.
  3. Valverde A, Hamilton C, Moro C, Billeres M, Magistretti P, Mitrofanis J. Lights at night: does photobiomodulation improve sleep? Neural Regen Res. 2023 Mar;18(3):474-477. doi: 10.4103/1673-5374.350191. PMID: 36018149.
  4. Pail G, Huf W, Pjrek E, Winkler D, Willeit M, Praschak-Rieder N, et al. Bright-light therapy in the treatment of mood disorders. Neuropsychobiology 2011;64:152–62.
  5. Campbell PD, Miller AM, Woesner ME. Bright Light Therapy: Seasonal Affective Disorder and Beyond. Einstein J Biol Med. 2017;32:E13-E25. PMID: 31528147; PMCID: PMC6746555.
  6. Nussbaumer-Streit B, Forneris CA,Morgan LC, Van NoordMG, Gaynes BN, Greenblatt A,Wipplinger J, Lux LJ,Winkler D, Gartlehner G. Light therapy for preventing seasonal affective disorder. Cochrane Database of Systematic Reviews 2019, Issue 3. Art. No.: CD011269. DOI: 10.1002/14651858.CD011269.pub3.