What is the best time of day to use Red Light Therapy?
Many of us want to make sure we are using our red light devices optimally. From parameters like intensity, wavelengths, dosage, beam angle, and EMFs - it is easy to get caught in the weeds sifting through the data.
Our biology is inexorably tied to our circadian rhythm not only to determine our bedtime, but everything from meal-timing to hormone production may be correlated to our internal body clock. We know that obviously the sun is the most potent modulator of of circadian rhythm with it's bright full-spectrum output.
So it is natural to assume that our biological response to light therapy devices might also be driven by the circadian rhythm. More importantly in this modern era of indoor living and artificial lights, we must also consider how our light therapy will impact our circadian rhythm.
While the science of photobiomodulation does not provide definitive answers for us on the topic, there are some good practices we can follow to make sure we are using Red Light Therapy in harmony with our biology.
The truth of the matter is, that most of the science on Red Light Therapy does not account for the time of day. For example if you open up any of the thousands of studies on Pubmed on LLLT or PBM, none of them ever mention about the time of day that they administer the treatment (4). We might assume that most treatments are being conducted during regular office hours on weekdays.
It is likely that most scientists are not aware that light therapy can have different effects at different times of day. Similar to how most diet studies don't consider meal timing or circadian disruption as a major factor of the diet's success, many light-based studies are also ignorant that timing might affect the outcomes.
The good news is that despite not taking note of time of day, scientists get fantastic results with red light therapy nonetheless! That means that we can essentially use red light therapy any time of day and get good results. So fit in your red light therapy anytime that it is convenient!
Unfortunately this means that there are no clear examples of studies that compare "treatment at 8AM versus 8PM." The science is assuming that red light therapy is an independent variable with respect to time of day. So we have to look somewhat outside of traditional LLLT and PBM studies to learn more.
For those of us engrossed in being mitochondriacs and tracking our circadian rhythm, the above answer is simply not enough! We want to optimize our circadian rhythm as well as get awesome results from light therapy.
So the primary resources we should be looking for are studies of our evolutionary nature (sunlight) as well as the factors that affect sleep and circadian biology. Once we understand the cycles of the sun and the light that our body is adapted to use, then we can correlate that to our red light devices.
2. a. Sleep Cycles
Our sleep cycles are closely entrained by the light that we are exposed to (primarily through the eyes). Using the correct light and wavelengths can keep us in sync with our natural sleep rhythm, while the wrong light might throw off our circadian rhythm. This may be important to make sure we have enough energy for the day, and be restful at night.
For example a wake-up light is typically around 10,000 lux and contains full-spectrum (white) light. This primarily acts to suppress melatonin production and start the alertness response (5). While a bright white light might work best for this purpose, there has been a study to show that bright red light can also shut off melatonin production (3)! To hack this piece of information, we should do our facial treatments with red light therapy in the morning, to optimize our wake-up response at the same time of getting our red light therapy. A win-win!
The good news is that low lux red lights are generally not going to harm melationin production, especially if you look at the well-defined Melationin Suppression curve and Scoptopic sensitivity curve. So as long as we avoid doing red light therapy on the face at night, we can successfully enjoy it on other parts of the body! In fact, some studies indicate that red and near-infrared light on the body and organs may promote melationin production. This study indicates that directing this energy towards the thymus gland (chest) may help promote natural melationin production! (6) So at nighttime, it might be best to use red light therapy over the chest or other areas for best circadian alignment, while avoiding directly on the face.
2. b. Solar Spectrum Cycle
Of course our guiding reference point should be the sun! Can we use Red Light Therapy to help mimic the sun? Not exactly, but when we are mindful of the similarities we can learn how to optimize the use of red light therapy.
When we break up the solar day into pieces, the three main parts are the Morning, Noon, and Evening. The Morning and Evening are somewhat similar where the sun is closer to the horizon and projecting light at an angle to the earth, while at Noon the sun is right overhead. When you experience the sun at high-noon on a sunny day, you certainly can feel the intensity and brightness. While in the morning and evening the sun feels softer with more inviting colors like yellow and red in the horizon and clouds.
The concept of Rayleigh Scattering as well as the absorption windows for the atmosphere determine the light spectrum we experience at those times of day. In the morning and evenings the sunlight is filtered and scattered more, removing much of the UV and blue before it reaches you. More of the heat-inducing mid and Far-Infrared is filtered from the water in the atmosphere. This time provides us with the highest ratio of Red and Near-Infrared wavelengths naturally from the sun, with less from the rest of the spectrum.
With this analogy of the sun, it may be suitable to try to use our Red and Near-Infrared light at the morning and evening time as this may be likely the primary times that our ancestors were exposed to such light. One study indicates the morning as "PBM Pre-Conditioning" and evening as "PBM-Repair" (1). Similarly we may use the sun or our Red Light Therapy devices in the morning to help prepare ourselves for the day, then again at night to initiate the repair process.
Of course our ancestors did use some artificial light as well, in the methods of campfires and candles! So it is natural also to assume our bodies were regularly exposed to red and infrared from fires after the sun goes down. This too, may be a good analogy to reference when understanding our evolutionary exposure to red and infrared light.
While we want to always have the optimal experience with our biohacks, sometimes we just need to fit it in whenever we can! Stacking our devices around our busy schedule is sometimes the only way we can fit everything in. So far there is not any definitive science to tell us the best time of day to use Red Light Therapy.
However we know that we evolved in conjunction with spectrum and routines set by the sun. If we use that as the guide, it may be reasonable to assume that our bodies are well-tuned for red light therapy in the mornings and evenings, as those are the times of day that the proportion of sunlight favors red and infrared.
Disclaimer: All information in this article and website are intended for educational purposes only. It is not intended to treat, diagnose, or cure any ailment. Please consult with your doctor or trusted wellness practitioner before starting any new health activity including Red Light Therapy.
Barolet D, Christiaens F, Hamblin MR. Infrared and Skin: Friend or Foe. J Photochem Photobiol B. 2016.
(2)Denis OdinokovMichael R. Hamblin
Aging of lymphoid organs: Can photobiomodulation reverse age-associated thymic involution via stimulation of extrapineal melatonin synthesis and bone marrow stem cells?
"High-intensity red light suppresses melatonin."
Low Level Laser Therapy (LLLT) spreadsheet
What keeps us awake? The role of clocks and hourglasses, light, and melatonin.