Shopping cart



The “Re-Timer” Effect: How To Re-Time Your Circadian Rhythms If You Wake Up Too Early Or Stay Up Too Late.

Affiliate Disclosure

Article-new, Articles, Biohacking, Body, Longevity & Age Reversal, Recovery & Sleep

Some people say they're most productive after midnight (*ahem* Tim Ferriss, Matt Mullenweg, etc.?).

Other people roll out of bed at 4AM because, well, frankly, they can't sleep in. Ever. Period (*ahem* Navy SEALs and other driven hard-chargers?)

I've got news for you: that ain't normal.

Below is a graphical representation of the sleep patterns of a normally timed, late timed and early timed body clock. Your normal circadian rhythm is ideally timed to the top graph: the normally timed body clock.


In other words, in an ideal 24 hour cycle, you're supposed to wake up sometime between 6am and 7am and you're supposed to go to bed sometime between 10pm and 11pm. It's just the way we humans are wired.

Unfortunately, airline travel, jet lag, modern lighting, electronic screens, WiFi and bluetooth signaling and other cues that fly in the face of natural daily sunlight and natural evening darkness can throw your body clock entirely out-of-whack. Rather than fixing the problem, most people will simply begin making excuses that they're a “night owl” or an “early bird”, all while beating up their biology with an unnatural circadian rhythm alignment.

Why is this so important?

Check out the graph below to see how your physiology, biology, health and longevity are tied to a normal circadian rhythm (admittedly low-resolution, but you'll get the picture):


So if that circadian rhythm pictured above isn't optimized and your body's clock is not timed properly, your hormones will suffer, your fertility will suffer, and your longevity will suffer. In today's article, I'm going to teach you exactly how to use something called the “Re-Timer” and the use of green-blue spectrum of light to shift a delayed, late-timed body clock back to where it needs to go, and how to shift an advanced, early-timed body clock back to where it needs to go.

How Light Regulates Your Circadian Rhythm

Before you learn how to shift your body's clock, it's important to understand how your body's clock responds to the cue of light.

Light is electromagnetic radiation that specifically falls within a certain part of the electromagnetic spectrum. The word “light” usually refers to visible light, meaning light that is visible to your eye and is responsible for your sense of sight. Visible light is specifically defined as light that has a wavelength in the range of 400-700 nanometres (nm), which falls just between infrared light (which is light with longer wavelengths) and ultraviolet light (which is light with shorter wavelengths).

For the purposes of this article, when I say “light”, I’m referring to visible light. That doesn't mean other forms of non-visible light, such as infrared and UV light, aren't important. I discuss the former in nitty-gritty detail here and am working on another post about how to intelligently use the latter without getting skin cancer (for now, you can check out the fascinating way that your skin melanin can act like a natural solar-panel in this article about in this article about the role of melanin in converting ultraviolet light into metabolic energy)

But in the meantime, let's focus on visible light.

The main natural source of visible light on earth is, you guessed it, the sun. Sunlight provides the energy that green plants use to create starches, which then release energy into the living things that digest those starches. This process of photosynthesis provides just about all the energy used by life on earth.

Another important source of light for humans is fire, which includes everything from ancient campfires to modern kerosene lamps. Of course, with the development of electric lights and power, electric lighting has pretty much replaced most firelight.

Some species of animals generate their own light, called bioluminescence. For example, fireflies use light to locate mates, and vampire squids use light to hide themselves from prey. Even humans emit small amounts of biophotons of light (see below from this fascinating article on human light production)

“Indeed, the human body emits biophotons, also known as ultraweak photon emissions (UPE), with a visibility 1,000 times lower than the sensitivity of our naked eye. While not visible to us, these particles of light (or waves, depending on how you are measuring them) are part of the visible electromagnetic spectrum (380-780 nm) and are detectable via sophisticated modern instrumentation.”

And yes, that light emitted by the human body can even be photographed, via a process called “Gas Discharge Visualization” (GDV), which you can read about in detail here, and which I am also working on a separate blog post/podcast about.

Anyways, back to visual light. The specific properties of light are generally measured in terms of intensity, propagation, direction, frequency or wavelength, and polarization. The speed of light, measured in a vacuum, is 299,792,458 meters per second, and is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation (EMR), is experimentally found to always move at this speed in vacuum.

Just as crucial as your understanding of light is going to be your understanding of the circadian rhythm

Often referred to as the “internal body clock”, the circadian rhythm influences the timing of all our bodily rhythms, including our sleep-wake rhythm. The cycle is completed approximately once every 24-hour period, which is why these regular rhythms are called circadian (circa=about, dian=day) rhythms.

Circadian rhythms are physiologic and behavioral cycles with a recurring periodicity of approximately 24 hours, generated by an endogenous biological pacemaker called the suprachiasmatic nucleus (SCN), which is located in the anterior hypothalamus in brain. These circadian rhythms control a huge variety of biological processes, such as sleep- wake cycle, body temperature, feeding, hormone secretion, glucose homeostasis, and cell-cycle regulation.

Let's take another glance at the graph I already showed you above so you can see what I mean:


Here's another good example, slightly less grainy:


The timing of these physiologic circadian rhythms can become altered, leading to changes in the phase relationship of rhythms to each other, which can cause internal desynchronization. Sometimes this desynchronization manifests as jet lag, sometimes as insomnia, sometimes as waking up extremely freaking early even though all you really want to do is just sleep in a little bit.

As you may have experienced at some point in your life, a loss of coordination of these rhythms can have negative consequences on your productivity, your appetite, your happiness, your social interactions, your workouts, your focus, your immune system and many other physiologic and behavioral functions.

So ultimately, the less desynchronized your circadian rhythms are, the better your life. This is mostly related to a big disruption in the production of monoamines and hormones that affect your sleep-wake cycle and wellbeing, including melatonin, serotonin, dopamine, noradrenalin, leptin, ghrelin, etc.

Via a process called “circadian entrainment”, circadian rhythms are synchronized with the earth’s rotation by daily adjustments in the timing of the SCN (remember, that’s the part of your brain I mentioned earlier), and the circadian rhythms generally follow the exposure to stimuli that signal the time of day. These stimuli are known as zeitgebers (German for ‘‘time-givers’’), and while zeitgebers can include everything from the time of day that you exercise, to when you eat breakfast…

…light is the most important and potent stimulus for circadian entrainment.

I will repeat this.

Light is the most important and potent stimulus for circadian entrainment.

The magnitude and direction of any changes in circadian rhythms directly depends on when within the circadian rhythm that a light pulse is presented to either your eyes, or your skin, or anywhere else on your body that light photoreceptors are located. You can actually plot phase changes in circadian rhythm according to the time of light stimulus presentation, and this plot provides what sleep scientists call a “phase response curve”.

For example, exposure to light in the morning and exposure to darkness at night results in a phase response curve that can shift your circadian rhythm backwards and make you sleepy at a more appropriate time in the evening, while exposure to light in the evening or non-exposure to light in the morning can slightly shift your circadian rhythm forwards and cause you to stay awake longer and possibly sleep in longer in the morning, although sleeping in longer in the morning usually requires more of an absence of morning light than a presence of evening light.

What Happens When Your Circadian Rhythm Gets Messed Up

Circadian rhythm sleep disorders (CRSDs) is the term given to patterns of sleep-wake rhythm disturbances. CRSDs result from a misalignment between the timing of the circadian rhythm and the external environment (e.g. jet lag, shift work, watching loud and bright TV at night, etc.) or a dysfunction of the circadian clock and its afferent and efferent pathways (e.g. delayed sleep-phase, advanced sleep-phase, non-24-hour, and irregular sleep-wake rhythm disorders, such as might occur with obstructive sleep apnea, parasites, nighttime hypoglycemia, etc.).

The most common symptoms of these disorders are difficulties with sleep onset or sleep maintenance, and excessive sleepiness that is commonly associated with impaired social and occupational functioning.

Effective treatment for most CRSDs requires a multimodal approach to accelerate circadian realignment with exposure to appropriate amounts of light at specific times of day, avoidance of bright light at inappropriate times, adherence to scheduled sleep and wake times and some of the other strategies Dr. Joe Zelk discusses in this article and this podcast.

Now, let's return to a familiar graph you've already seen up above:


You now know that the early timed and late timed body clocks are simply perfect examples of a CRSD.

Delayed Sleep Phase Disorder (also referred to as sleep onset insomnia) can cause you to have difficulty falling asleep at your desired bedtime. Typically, you would be unable to sleep until after midnight and then find it difficult to wake up early in the morning for school or work commitments.

Advanced Sleep Phase Syndrome (also referred to as early-morning awakening insomnia) can cause you to feel overwhelmingly sleepy during the early evening, essentially rendering you unable to stay awake. Your “ideal” bed time may be as early as 7pm, causing a wake time of around 3am, which significantly impacts your work and social life.

Either of these circadian rhythm mismatches can result in the following:

-Poor sleep quality
-Insufficient sleep duration
-Sleepiness and fatigue
-Impaired overall well-being in family and social life
-Decreased motor and cognitive performance
-Poor neuronal and muscle healing
-Appetite dysregulation
-And much more…

So what exactly is it that can disrupt your circadian rhythm like this and cause a CRSD?

In a nutshell, sleeping and waking difficulties occur when there is a discrepancy between the circadian rhythm and your preferred sleep period. This can occur for a number of reasons, including:

Lifestyle factors: lack of bright light in morning and presence of bright light at night can shift your circadian rhythm forward. Too much bright light too early in the morning and “shutting off” exposure to light too early in the day can shift your circadian rhythm backwards.

Shift work: working different shifts requires you to adjust your sleep-wake times to accommodate your work life. Often this means having to sleep during the day, which is contrary to your body’s natural rhythm, or experiencing fatigue during your shift. 

Travel: frequent travel may require you to cross multiple time zones. This can disrupt your existing sleep-wake rhythm and result in you feeling jet lagged and unable to sleep. 

Seasonality: lack of morning light during the winter can cause you to have trouble sleeping at night and then waking in the morning. 

If you want more nitty gritty details on CRSDs, you can download Circadian Rhythm Abnormalities (.pdf download). Just like I described earlier in this article, you'll see that for each of these lifestyle and biological factors, appropriately timed bright light therapy is the most effective method for re-timing circadian rhythms and consequently improving sleep and biological function.

OK, let’s sum up where we are at this point:

You now understand now that light is the single strongest signal that keeps your biological clock synchronized.

You understand that if you don’t get enough light during the day or you get it at the wrong time of the day, e.g. during shift-work or travel induced jet lag, your biological clock can go out of sync, and the production of neurotransmitters and hormones that affect your sleep-wake cycle and wellbeing.

And you understand that this can have a negative effect on how you feel and function during the day and how you sleep during the night.

What is Light Therapy?

Enter light therapy.

The information your body gets about existence or absence of light is received via light-sensitive receptor proteins in the eye’s retina. These proteins are called opsins. Opsins convert the photonic energy of light into electrical potential in neurons, and project signals from light to the brain’s biological clock, as well as to other brain areas. This then increases neurotransmitter signalling and influences hormone production. These light-sensitive receptors are not only found in the retina, but also in many locations in your brain and body, such as the cerebrum, the hypothalamus, inside your ears and on every inch of your skin (which is why, by the way, it's very important when you sleep in darkness at night to not just limit light exposure to your eyes, but also to your skin).

You already know that the most important external indicator to help keep your body synchronized with this routine is light. Sure: exercise, food, air, etc. all effect your body's clock, but nothing beats light.

Why is light so important to your circadian rhythm? Because when your eye senses light, it sends a signal to your brain to be awake. As it becomes dark in the evening, your body produces melatonin, telling your body it is time to sleep. The combination of biological processes in response to light and darkness are crucial factors for your body to remain synchronized and sleep at the right time.

If you do not receive light at the right times due to the winter months or lifestyle factors or shift work or jet lag or any of the other contributing factors I've covered already, this can confuse your circadian rhythm, leaving you unable to sleep when you need to and contributing to all the biological issues described above.

Light therapy (also known as phototherapy) simply involves exposure to specific wavelengths of light for a prescribed amount of time at a specific time of day. For example, morning bright light therapy can adjust your body clock to an earlier schedule through repeated exposure to bright light appropriately timed in the morning. Evening bright light therapy can re-time your body clock to a later time by exposing you to bright light visual stimulation in the evening.

Again, this all works because light exposure is your body's primary cue to regulate your body clock. 

What Kind Of Light Is Best For Light Therapy?

Bright light therapy has been used to treat the winter depression of Seasonal Affective Disorder (SAD) for decades. According to Mayo Clinic, light therapy is the most recommended and main form of treatment for Seasonal Affective Disorder. Traditionally white light therapy has been used, however research has now shown that white light may not actually be the most effective form of light therapy, and may even cause retinal damage if overused.

Instead of harsh white light, green-blue light has actually been proven to be more effective at re-timing the body clock and suppressing the production of melatonin (Lack et al. 2004).

One reason for this is because our eyes contain a lens that becomes cloudy and yellows as we age. This clouding actually restricts blue light from entering the eye. Since most white light emitting devices (often called “blue light boxes”) rely solely on blue wavelengths, green-blue light is actually considered to be a superior treatment option in older populations.

Research has actually looked at compliance to treatment with these white light emitting boxes and found that not only is the white color not the correct color, but compliance is quite low, probably because it's quite difficult to lead a busy life and spend time each morning sitting still while staring at a light box. Later in this article, you'll see that practicing sleep psychologists have invented portable light therapy that not only contains more of the physiologically appropriate green-blue light wave spectrum, but also increases compliance to light therapy treatment.

The majority of research has found that your circadian clock can be advanced to an earlier time or delayed to a later time when using light comprising a peak wavelength in the green-blue spectrum. Let's take a look at some of the research that shows green-blue light to be superior to white light when it comes to re-timing your body's circadian rhythms.

Wright HR, Lack LC & Partridge KJ, ‘Light emitting diodes can be used to phase delay the melatonin rhythm’, Journal of Pineal Research, 2001, 31:350–355.

Objective: The aim of this study was to compare the effect of a portable light source with that of a conventional light box in suppressing nocturnal salivary melatonin and phase shifting dim light melatonin onset (DLMO), a phase marker of the circadian system [Lewy and Sack 1989].

Method: Two portable light sources, comprising light-emitting diodes (LEDs) of two different wavelengths, were compared to a standard light box in suppressing and phase shifting nocturnal salivary melatonin. All light sources were equated for illuminance of 2000 lux. Sixty-six volunteers participated in the two-day study and were randomly allocated to one of four conditions: light box, white LED, blue-green LED, or no light control group. Light was administered to the experimental groups from midnight to 02.00 on the first night.

Half-hourly saliva samples were collected from 19.00 to 02.00 on night 1 and until 01.00 on night 2. Per cent melatonin suppression on night 1 and dim light melatonin onset (DLMO) for each night were calculated.

Conclusion: The experimental groups showed significant melatonin suppression during light stimulation, with the blue-green LEDs producing the greatest (70%) suppression.

There was no significant difference between the light box at 63% and white LED at 50% suppression. Similarly, the blue-green LED had a significantly greater DLMO delay of 42 minutes and there was no difference between the light box of 23 minutes and the white LED of 22 minutes. These data suggest the portable LED light source is an effective way of delivering light to phase shift the melatonin rhythm, with the blue-green LED being the more effective of the two LEDs.

Wright, HR, Lack, LC & Kennaway, DJ, ‘Differential effects of light wavelength in phase advancing the melatonin rhythm’, Journal of Pineal Research, 2004, 36:140–144.

Objective: Shorter wavelength light has been shown to be more effective than longer wavelengths in suppressing nocturnal melatonin and phase-delaying the melatonin rhythm. In the present study, different wavelengths of light were evaluated for their capacity to phase advance the saliva melatonin rhythm.

Method: Light was administered via a portable light source comprising two light-emitting diodes per eye, with the irradiance of each diode set at 65 lW/cm2. Forty-two volunteers participated in up to six conditions resulting in 15 per condition. For the active light conditions, a 2-hour light pulse was administered from 06.00 on two consecutive mornings. Half-hourly saliva samples were collected on the evening prior to the first light pulse and the evening following the second light pulse.

Conclusion: The shorter wavelengths of 470, 495 and 525 nm showed the greatest melatonin onset advances ranging from approximately 40 to 65 minutes while the longer wavelengths produced no significant phase advance.

These results strengthen earlier findings that the human circadian system is more sensitive to the short wavelengths of light than the longer wavelengths.

Lack, L, Bramwell, T, Wright, H & Kemp, K, ‘Morning blue light can advance the melatonin rhythm in mild delayed sleep phase syndrome’, Sleep and Biological Rhythms 2007, 5: 78–80

Objective: We investigated the effectiveness of morning blue light in advancing the sleep and melatonin rhythm of individuals with mild delayed sleep phase syndrome.

Method: The 18 participants were randomly allocated to a light or control group. Wake-up times were gradually advanced to 06.00 over a week, during which the light group also received two hours of blue light immediately after waking. During the treatment week that followed, the blue light group was exposed to two hours of blue light each morning, starting immediately after waking up. The portable light source comprised blue light LEDs (470 nm peak wavelength with irradiance of 65 μW/ cm2) attached to the lower rims of spectacle frames.

Conclusion: The blue light group showed a significant 2.53-h advance of dim light melatonin onset, compared to no change in the control group. However, neither group had a significant advance of sleep times following treatment. Effective delayed sleep phase syndrome treatment may require adjunct behavioral instructions.

Wright HR, Lack LC, ‘Effect of light wavelength on suppression and phase delay of the melatonin rhythm’, Chronobiology International, 2001 Sept., 18 (5): 801–8

Objective: Different wavelengths of light were compared for melatonin suppression and phase shifting of the salivary melatonin rhythm. The wavelengths compared were 660 nm (red), 595 nm (amber), 525 nm (green), 497 nm (blue/green), and 470 nm (blue).

Method: Volunteers were administered with light-emitting diodes equated for irradiance of 130 muW/cm2. Fifteen volunteers participated in all five wavelength conditions and a no light control condition, with each condition conducted over two consecutive evenings. Half-hourly saliva samples were collected from 19.00 to 02.00 on night 1 and until 01.00 on night 2. Light was administered for the experimental conditions on the first night only from midnight to 02.00.

Conclusion: Percentage melatonin suppression on night 1 and dim light melatonin onset (DLMO) for each night were calculated. The shorter wavelengths of 470, 497, and 525 nm showed the greatest melatonin suppression – 65% to 81%. The shorter wavelengths also showed the greatest DLMO delay on night 2 – ranging from 27 to 36 minutes. The results were consistent with the involvement of a scotopic mechanism in the regulation of circadian phase.

Olsen, B, Szkibik, N & Chau, A, ‘Green light is effective in advancing the timing of sleep onset and increasing duration of sleep’, 2013 August.

Note: This study was a non-clinical consumer trial and has not been published in a scientific journal or peer-reviewed.

Objective: We investigated the ability of green light to advance sleep onset to an earlier time and increase sleep duration. The 24 participants were asked to nominate their current sub-optimal sleep–wake times and their preferred earlier or ideal sleep–wake times. A custom schedule was prepared for participants detailing the times to wear Re-Timer.

Method: During the treatment week participants were asked to use the green light device for 50 minutes each 24-hour period for 7 days. All participants used the device in the morning shortly after waking (M = 8.42 am, SD = 2.23 hours). Wake-up times and exposure to green light were gradually advanced by an average of 8 minutes each morning, starting from each participant’s usual wake-up time. The choice of bedtime and wake-up times across the week were self-selected. Participants were asked to use the device for only 50 minutes at the prescribed time. After waking, all participants followed their usual morning routine while wearing a Re-Timer device. Participants recorded their sleep–wake routine during the treatment week in a sleep diary. The study was carried out in winter with morning light levels

Conclusion: Baseline data provided by participants prior to the trial showed the average sleep onset time was 1.47 (SD = 82 minutes). The average preferred sleep onset time participants wanted to achieve was 23.00 (SD = 56 minutes). This would be an average advance in sleep onset of 2 hours and 47 minutes, a significant change in the circadian clock. 92% (n = 22) achieved a movement towards their preferred sleep onset time; 8% did not realize any movement in their sleep onset time. An average advance of 2 hours and 30 minutes was achieved across the sample (n = 24).

For green light to be considered an effective treatment option, duration of sleep should either be constant or increase as sleep onset time advances. Reduced sleep duration would result only in sleep debt. Average sleep duration before the study was 7.1 hours (SD = 1.4 hours). On the 7th day of use, average sleep duration of participants was 7.8 hours (SD = 1.92 hours), an increase over the baseline measure by 0.7 hours (42 minutes).

Based on the studies above, green-blue 500nm dominant wavelength, UV-free light is the most superior form of visual light to expose your eyes to when it comes to aligning your circadian rhythm. Green-blue light is most effective at re-timing your body clock. 

How To Use Green-Blue Light

If you pay attention to my Instagram and Snapchat feeds, or to biohacker Dave Asprey, it's no secret that we personally use green-blue light for the eyes, especially after a bout of travel or circadian rhythm disruption.

Lately, you may have seen me wearing a slightly odd-shaped set of white eyewear that produces the exact spectrum of green-blue light I described earlier in this article.

The set of white eyewear, is called a “Re-Timer“. Re-Time Pty Ltd is the company that makes the Re-Timer, and was formed in 2010 to help people re-time their body clocks and improve sleep. Initially, led by Professor Leon Lack from Flinders University, Re-Timer has been researching and developing the world’s first wearable green-blue light therapy device since 1987.

Over the past several years, a team of seven engineers, two ophthalmic experts and two sleep psychologists designed the Re-Timer. Over one year (1,900 hours) of work time was spent on computer-aided design alone as the team worked to incorporate the latest sleep science from Flinders University into an ergonomic, lightweight and portable wearable device. Four design iterations and 160 logged design changes later, Re-Timer was launched worldwide in November 2012.

Since then, thousands of units have been sold worldwide. Today, Re-Timer is assembled in a state of the art clean room, in Adelaide, Australia, and has been sold in more than 40 different countries worldwide. It is actually the world’s number one selling wearable light therapy device.

The team at Re-Timer is led by Professor Leon Lack (pictured below), who is a Clinical Psychologist at the Adelaide Institute for Sleep Health (AISH). He is also a Professor of Psychology at Flinders University.


Dr. Lack is acknowledged internationally as one of the world’s leaders in behavioral management of insomnia and has conducted extensive research in sleep, circadian rhythms and insomnia over 30 years. For the last 20 years he has directed a clinic for the non-drug treatment of insomnia at AISH and has supervised many clinical Masters and PhD students in this area. He was a co-founder of the Australasian Sleep Association and its president from 1989 to 1992.

Leon is also the author of 80 peer-reviewed journal articles and has received research grants from bodies including the Australian Research Council and National Health and Medical Research Council. Leon earned his PhD from The University of Adelaide and received his Bachelor of Arts from Stanford University.

Here's how the Re-Timer works.

You simply wear it while you are awake either in the morning or evening, depending on how you want to change your sleep. For example, one recommended schedule to change your sleep is typically seven days for 30 minutes each day. To treat Winter Blues, Re-Timer can be worn daily throughout winter or just used on the darker colder days when you want to boost your energy and mood.

It delivers light at the optimal delivery angle. Most light entering the eye is from below, so the Re-Timer replicates this. If light were delivered from above it would be blocked by your eyebrows, diminishing performance.

The Re-Timer light is UV-free and has been independently tested for eye safety to the international standard CEI IEC 62471. It comes with an embossed travel case, a USB cable for re-charging, a long lasting lithium ion battery and a 1-year warranty.

Here are more specs:

Size 7.9” 5.5” x 2.2” or 200 x 140 x 55 mm. One size fits all.
Weight 2.64 ounces or 75 grams (product only)
Lighting technology 4 Light-emitting diodes (LEDs), 0.1 watts, diffuser cover technology
Light spectrum intensity Green-blue 500 nm dominant wavelength, UV-free light
High setting is 506 Lux lm/m² and 230 µW/cm²
Low setting is 315 Lux lm/m² and 143 µW/cm²
Light pulse 50 to 166 hertz. Not suitable for those who suffer epilepsy or similar conditions.
Useful life >10,000 hours
Battery Integrated rechargeable Li-ion polymer battery, 3.7V, 200mAh
Battery life Up to 4 hours
Technical warranty 1 year
Manual English / Japanese
Accessories USB cable for charging battery via PC or USB compatible 5V wall socket
Premium embossed travel case



Basically, you can consider the Re-Timer to be the complete polar opposite of blue-light blocking glasses. Blue-light blocking glasses block blue light from entering your eyes, while the Re-Timer shines into your eyes with green-blue light far more powerful than what you'd get from a phone, television, computer, etc. When you use the two of them strategically throughout the day, you can tweak your circadian rhythm forwards or backwards, whichever you choose.


How To Use The Re-Timer

There are a few different ways I have used my Re-Timer to adjust my circadian rhythm.

First, for 1-3 days before I travel from East to West across multiple time zones, I can wear them for 30 minutes when it’s morning where I’m going. So if I want to be wakeful at, say, 7am in the West, I’ll use the Re-Timer at 10am in the East.

Then, when I’m in the West, I simply use the light for another 30 minutes either when I wake up or while I’m sitting drinking coffee and checking my emails. I'll also wear them in the sauna, while walking around outside, during a workout, etc.

Next, I’ve had a few races for which I’ve had to wake up 1-2 hours before my normal waking time. In these instances, I’ve instantly eliminated the normal grogginess from getting up earlier than usual by simply using the Re-Timer as soon as I wake up in the morning.

On several occasions, I’ve worn the Re-Timer on a sunless day and used it just after lunch, when afternoon sleepiness and mild amounts of seasonal affective disorder would normally set in. Both times, it’s completely eliminated the need for a nap, and although it could certainly be a placebo effect, seems to lift my mood, focus and cognitive performance as well.

I’ve also had several times since getting my Re-Timer that I’ve gotten into a pattern of waking up too early (which you know now is a mis-timed circadian rhythm), such as at 5:00AM, when I’d rather sleep until 6:30AM. Each time, I’ve pulled myself out of that pattern by getting up at 5:00AM, avoiding any sun exposure and wearing blue-light blocking glasses, and then at 6:30AM (the time I’d rather be waking up), wearing the Re-Timer for 30 minutes. So in this way, I can shift my circadian rhythm forwards, or backwards.

The Re-Timer could also be used when you’ve traveled to, say, the West. Let’s say you have a party, a dinner, a social event, a conference, a speech, a meeting, etc. at 7pm, which for you, if you come from the East, would be, say, 10pm. You could use the Re-Timer beforehand for a quick blast of energy as an alternative to caffeine or some other stimulant.

The Re-Timer website also has a Jet Lag Calculator that will tell you when to receive light to reduce jet lag. Sleep scientists Professor Leon Lack and Dr. Helen Wright, who I mentioned above, developed this algorithm, which considers your departure and arrival cities, as well as your current sleep pattern. The calculator is also available as a free iPhone App.

In addition, they have an easy-to-use Sleep Calculator. To use it, you simply select from a drop down menu:

-Whether you wish to change the time you sleep or the time you wake
-The desired time you wish to sleep or wake
-The time you currently wake
-The time you currently fall asleep

A customized schedule is then generated for you, based on the information you entered. The schedule will outline the best time to wear Re-Timer glasses to change your sleep times.


All of this is especially important information for you if you, like me, are a frequent airplane seat occupier. As a matter of fact, there are only three proven treatments for jet-lag that have been systematically explored under laboratory and field conditions:

1) exposure to bright light;

2) high-dose melatonin supplements;

3) pharmacological agents – that is, medication.

Of all these three options, only bright light exposure has none of the side effects or risks known to be associated with the use of high doses melatonin or pharmacological agents used to treat and avoid jet lag symptoms.

But from shift work, to an annoying habit of waking up too early, to not having any productive time until late at night, to other forms of circadian rhythm disorders, this type of device can be used for far more than simply jet lag and airline travel.

And for you true circadian rhythm biohackers out there, in an ideal “morning habit” scenario, or after landing in a new destination across multiple time zones, you can throw in a bit of infrared saunacold thermogenesis and kundalini yoga too.

That's it.

If you're waking up super early, that's not normal. It's a disorder. It can eventually kill your biology.

The same goes with a propensity to stay up late.

So fix yourself.

You can click here to order a Re-Timer. Use discount code BGFITNESS  for $30 off your purchase.

Do you have questions, comments or feedback about the “Re-Timer effect”, how to re-time your circadian rhythm, the Re-Timer or anything else from this article? Leave your thoughts below and I'll reply.


Ask Ben a Podcast Question

Related Posts

50 thoughts on “The “Re-Timer” Effect: How To Re-Time Your Circadian Rhythms If You Wake Up Too Early Or Stay Up Too Late.

  1. Kim says:

    For most of us with hardcore DSPS, light and melatonin therapy simply does not work. We have to just learn to adapt to a different sleep schedule. But you never know until you try it. The light glasses are great in theory but they’re not as strong as a SAD light.

  2. Gabriel says:

    Hi Ben,

    Huge fan of the podcast and all of your work. I’m sure that the Retimer is a fantastic product that I will try when I’m not between jobs at the moment, and I was wondering if you had any recommendations/articles/podcast episodes you could recommend for a bare-bones approach to light therapy?

    For example would using your phone at full-brightness or exposing yourself to sunlight in the morning when you want to wake up make the same difference?



    1. Thank you for your kind comments Gabriel! Check out this resource:…

  3. Shivam says:

    Hey, most of the time I awake till 4 AM and didn’t get enough sleep. just 5 hours, could you help me.
    I tried but could not sleep in daylight.

  4. Philip Ly says:

    Ben you made a spelling error on paragraph one of “What is Light Therapy?”, being many not may.

    1. Philip Ly says:

      Scratch that it was supposed to be, “What Kind of Light is Best for Light Therapy”.

  5. Peter says:

    Hi Ben – your recent Kion article about sleep mentioned that light therapy boxes cause retinal damage. I see the same comment in this article. I use Re-Timers and light therapy boxes to reset my body clock when traveling internationally 5-6 times / year so I hate to hear that I might be damaging my retinas! Where can I learn more about the retinal risk from light therapy boxes? Many Thanks for this and everything you teach us.

  6. Martijn says:

    Hi Ben,

    Have you looked into Lumintte? They recently released the Lumintte 3 which seems to be pretty decent. Their light is not blue-green, but white enhanced to a certain blue range (468 nm). Curious to your thoughts!

    1. Martijn says:

      *Luminette typo

    2. Haven't tried those yet!

  7. Mallory says:

    Great article. Question, what are my options if I have to wake up at 5am for work, and not the ideal 6-7am? Would this work for me to “reset” my circadian rhythm?

  8. Daniele says:

    Hi Ben! Fantastic article as usual. I was gonna order this but as of May 2018, their iOS app is not available anymore as not compatible with iOS 11.
    Have you tried the AYO glasses (website is I would love to hear your opinion on those.

  9. Han-Lin says:

    I use a dawn simulator. Do you recommend additional light therapy?

    1. If you still need help with getting to bed or waking up, yes.

  10. David says:

    The discount code doesn´t seem to work anymore… has it expired? it was nowhere written on the article that it woudl

    1. For the Re-Timer? You used BGF30? Can you try again, and let me know if you're still having trouble. It's working on my end. Thanks!

  11. Hap says:

    What happens if you feel sleepy or groggy in the early evening….but if wait it out and end up on computer until 10 or so. Sleep quality not good according to Fitbit benchmarks. Too little deep sleep which is phase advanced from early night to early morning.

  12. Doreen says:

    My husband has purchased retimer glasses but has been told to wear in the evening then in the evening he need to sleep approximately 11pm until 7am when should he use the glasses

    1. In this case I would actually put them on at 7 AM for about 25 minutes

  13. ROSALI GOMES says:

    !M so confused! ! dont know the the right time to use the glasses so that I ca go to bed at 11 oclock pm and sleep for 8 hours. Please help me

  14. Ben Bokhout says:

    My wife has a diagnosis (melatonin 24h test) of ASPS (falling asleep ca 19-20h and, when aroused, sleeping again and again till 22.30h Wakes up at 2-3h in the morning)

    She tried the Re-timer > 1 month twice: first 2 h from 15-17h and then 1.5 h from 18.30 – 20h. Problem not solved.

    Please advice (=some schedule) we can try. Might using the Re-timer for 50 min. in the morning be worthwhile trying?



    1. Yes, she can use it for longer but make sure it is IN THE MORNING!

  15. Anup says:

    I am trying my re-timers in the morning for the first time for SAD. Ben, I read what you wrote above about using them around mid-day if no sunlight and low mood. I will try them then also.

    thank you Ben.

  16. Michael says:

    Hey Ben !

    Do you know any effects from wearing contact lenses on the circadian rhythm?

    i sleep terrible since i got contact lenses every day waking up at 4:30AM, weird times that i’m tired and active and so on..

    1. If they are colored lenses, then yes.. clear shouldn't be an issue.

      1. Michael says:

        thanks for the fast Reply! they aren’t colored but they are UV blocking?

  17. Robert T. says:

    Going to put these to the test as I am leaving from NYC for Tokyo on the 21st.

  18. Sally says:

    Thanks Ben! I saw these on Dave Asprey’s Facebook page last year and bought them. I love my re-timer goggles – great for jet lag and getting through the Seattle winters. Thanks for all the science, I didn’t know all of this info so thank you for sharing!

  19. James O'Brien says:

    Thanks Ben – another great post! I’ve used both Human Charger and Re-timers and I think the Re-timers work the best. A neurologist friend of mine told me about them – and I think that the research about green and blue light entering the photoreceptors in the eyes is very solid.

  20. David Stanford says:

    Very timely article Ben, since I just got home from a 6pm to 6am night shift when I came home and found this article. I really appreciate your superb breakdown of all the science. My question is, on a day like this where I’m coming off three nights how would I use the re-timer to fix myself?

    1. Re-Timer helps with night shift in three ways. 1. Wear it in the evenings before your first night shifts to stay up later and start shifting your circadian rhythm. This will help you prepare for night shift. 2. Wear it during night shift (or on a break during shift) to stay awake and alert, and to shift your most tired period (say 4am) to outside of your shift (to when you get home and want to sleep, say 8am) and 3. Wearing it in the morning when you’re coming off your shifts to get back into normal timing and regulate your sleep-wake cycle on your days off. The company creates schedules for shift workers, so if you email them your shifts they can customize a schedule for you.

  21. Hal Weiss says:


    I’m wearing blue blockers just reading this blogpost on my computer. I think it would be ill-advised to use blue light (or blue-green) in your eyes, since that’s probably one of the major causes of forniculated sleep. I’ve had upteen decades of fluorescent lighting in an office environment, tons of computer time, tablet time and phone time. Ergo, my sleep probs.

    All of these and non-native EMF’s are messing us up big time. I’ll try the human charger, and maybe by the vielight, but I’m not about to go this route. I think there’s a big danger in losing the DHA from your peepers with this devise.

    Just sayin’

    P.S. Love your site, love your book, love the blog.

    1. Dan Waters says:

      Light at the right times is good for you!! :) Light regulates our sleep and circadian rhythms. All white light contains blue and green wavelengths. We need light. If you have trouble falling asleep, you want UV free blue-green light in the mornings but then use your blue blockers at night when you’re on the computer. Light in the evenings is for when you’re flying west. Its all about the timing and the wavelength. Blue-green light is the most effective at stopping the release of the hormone melatonin. Ben’s right, there is a lots of research out there on this.

    2. The light is 100% UV-free and this device has been tested for ocular safety to the international standard CEI IEC 62471 which looks at blue light exposure. Blue-green light is a safe and effective way to adjust your circadian rhythm. If you have trouble falling asleep at night, get green-blue night in the morning and then wear you’re your blue blockers at night. You’d use green-blue light therapy in the evening if you wanted to be able to stay up later (say you’re preparing your body clock for a trip NY to San Fran). Exposing yourself to blue-green light is good if you do it at the right times. This light is important as it regulates your sleep-wake cycle and other biological processes (mentioned above).

  22. Jennifer says:

    Does wearing contacts change the effectiveness of the Re-timer?

    1. Clear contact lenses are fine. Tinted lenses / sunglasses can reduce the effectiveness of light therapy.

  23. Rob says:

    From your personal exp using them both, how would you compare this to the HumanCharger? Thanks Ben!

    1. I like BOTH, frankly. I still use HumanCharger and have even used both simultaneously (along with intranasal Vielight) to enhance effect even more. It's all about better living through science, baby.

      1. David Sanz says:

        I also jave the same question as Drew. If only one was possible, which one would you prefer?

        1. Totally depends. If sun not present …then retimer. If sun present, human charger…

    2. Drew says:

      If you can only afford to buy one, which would be your pick?

  24. Drew says:

    Great information! How does this differ from the human charger or intranasal light therapy? I know you’ve talked about both before.

    1. See my reply to Rob. Simply hitting a different section of your body (rods/cones)…

Leave a Reply

Your email address will not be published. Required fields are marked *