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How to Use Light Therapy to Change Your Internal Clock and Sleep Better

Use carefully timed light therapy to optimize your sleep

Do you feel very sleepy at 9 pm but want to stay up until 11?

Are you in bed at 11, yet can’t fall asleep for another hour?

Perhaps you have traveled across several times zones and now, even several days later, you feel sluggish and jet lagged.

All of the above are signs that your habits and desires and your biological clock are out of sync. And for most people the clock can’t be forced into sleep mode like an on-off switch.

Carefully timed light therapy, that is, exposure to blue, blue-green, or blue-enriched white light either in the evening or in the morning can be a fast and elegant way to set your clock to align with your lifestyle, sleep better, and even overcome serious insomnia.

My motivation for exploring light therapy for sleep

I often alternate between living in a small town for a few weeks and staying in a large bustling city. In the country side, folks are usually in bed by 9 pm; there is little else to do in the evening.

Quite quickly, I settle into a routing of having dinner, then watching TV for an hour or so – basically until I feel sleepy, which is usually pretty soon. So by 9 or 10 I am in bed and dozing off. I believe I have always been more of a lark, a morning person who tends to go to bed early and rises early. In fact, as I get older I become even more of an early riser.

This doesn’t suit me well when I am in the city though.

If I were to go to bed too early, noise would likely prevent me from falling asleep, and from hanging out with friends and drinking a few beers at night. Naturally my beer consumption also goes up when I am around town.

While in town, I would much rather go to bed at around 11:30 pm and maybe wake up at 7 or even 8. Being among other people and exposed to lots of light, I usually manage to stay up until 12 am and then go home and fall asleep quickly.

Unfortunately, I wake up at 4:30 or 5 am.

This would be fine when going to bed and 9 or 10, but with my later bed time I only get about 5 hours of sleep: a perfect recipe for feeling low on energy and sleep deprived.

It takes me quite a few days or even weeks to nudge myself into waking up later.

For many years, researchers at the sleep lab of Flinders University in Adelaide, South Australia have been researching the use of bright light therapy and blue-green light to help people optimize their sleep and overcome insomnia.

They were initially focusing on people with delayed sleep phase disorder (DSPD), also known as delayed sleep phase syndrome and advanced sleep phase disorder (ASPD), aka advanced sleep phase syndrome.

Now they are also applying their research to help frequent travelers overcome jet lag and shift workers adjust to a markedly different sleep-wake schedule.

In a way, you could even consider party people as shift workers.

Owls and larks and everyone in between

People with delayed sleep phase disorder (DSPD) are extreme night owls.

They can’t fall asleep before 2 am in the morning, and if they need to get up at a normal time like 7 o’clock to go to work or school, they feel like crap. They are constantly sleep deprived. If they go to bed earlier, they usually lie awake for hours. Their body just won’t listen.

People with DSPD usually sleep in on weekends to pay back some of their sleep debt. If they can go to bed when they feel sleepy and sleep as long as they want, they might sleep from 2 am to 10 am and feel completely rested.

Their problem is that their biological clock and the time demands society puts on them are incompatible.

A lot of teenagers have DSPD, and with schools starting at 8 am or earlier, they are constantly sleep deprived. They are bound to perform worse during class and exams. If only school started an hour or two later.

In fact, in 1910, schools in the US started at 9 am in the morning, and American educational psychologists criticized schools in Europe for starting way too early.

People with advanced sleep phase disorder (ASPD) on the other hand are larks, extreme morning people.

They might feel sleepy at 7 pm and if you let them, they might fall asleep at 8:30 pm. This is just the time when everyone is having fun or a nice dinner in town. In the morning then, they wake up at 4:30 am, when everyone else is asleep. They certainly don’t have a problem going to work or school on time – and perform well during normal office hours.

But being deprived of a normal social life because they would have to go to bed right after dinner, many larks decide to delay bedtime. They try to stay up until 11 pm like everyone else.

Their problem: They still wake up at 4:30 am in the morning, so they too accumulate a substantial sleep debt as they continue to enjoy their social “night” life.

Worse, they can’t even sleep in on the weekends!

We live in subjective time – set by our biological clock

Not everyone is an extreme night owl or lark, but we all have our own biologically programmed daily rhythm, also known as circadian rhythm.

If we don’t follow it, e.g., we go to bed when we are not sleepy, or we don’t go to bed when we feel sleepy, we are going to run into trouble.

Our personal circadian rhythm is run by a biological clock, the suprachiasmatic nucleus (SCN), which is a bundle of neurons located in a brain region called the hypothalamus.

As you probably know, our clock automatically re-adjusts itself as you move from one time zone to another. It just needs a little bit of time:

For example, the time difference between New York and Los Angeles is 3 hours.

Suppose you just moved from New York to LA. Your usual bedtime in New York is 11 pm, which is 8 pm in LA. On your first day in LA, you will likely feel sleepy at around 7 pm and go to bed a bit early, perhaps at 10 pm. You will also wake up a bit earlier. After a couple of days, however, you are back to your usual 11 pm bed time. Your internal biological clock has adjusted itself to Pacific Time. So now you are going to bed at 2 in the morning Eastern Time.

Can’t we just change the time zone without leaving town?

The main cue that resets the clock is light

Every morning, sunlight informs the SCN of “local time,” and the SCN uses this information to readjust itself.

Special photoreceptors at the back of our retina, so-called intrinsically photosensitive retinal ganglion cells (ipRGC) are connected to the SCN and relay light/dark information to the SCN.

These photoreceptors are most sensitive to blue and blue-green light, and almost insensitive to orange and red light.

This is not by accident: the sun’s light spectrum changes throughout the day. In the morning it is rich in blue, while in the evening it shifts to orange and red.

Light spectrum of the morning sun in Los Angeles

But it is not only sunlight that can reset the clock. Modern light sources like cold white LEDs contain large amounts of blue in their spectrum and are also affecting the clock.

So in principle, carefully timed light exposure with blue-rich light should allow us to adjust our clock and thus our sleep- and wakening times.

How light affects your clock depends on its intensity, its wave-length (blue and blue-green light have the strongest effect), and the subjective time your biological clock is currently set to.

Because blue and blue-green light have the strongest effect, they can be used quite effectively to change the timing of our internal clock and adjust it so that we can fall asleep at the time that is most convenient for us.

By the same token, however, if you arbitrarily use blue-rich light, you can disrupt sleep and set your biological clock to the wrong time. In fact, for many people who have trouble falling asleep, it makes sense to block blue light in the evening.

So how can you use light therapy to readjust the biological clock?

Our core body temperature is a good marker of our circadian rhythm. It rises in the morning, hovers around its maximum for a few hours, and then starts declining in the late evening. It reaches its minimum in the early morning, a few hours before awakening.

Body temperature variation over 24 hours in a normal sleeper

Light exposure before the temperature minimum sets our biological clock to a later time (delays it), white light exposure after the minimum sets it to an earlier time (advances it).

If you are too much of a lark, i.e., find yourself falling asleep too early in the evening and waking too early in the morning, you could use an hour of bright white light or blue/blue-green light in the late evening (before the temperature minimum) to delay your clock and thus fall asleep at a later time. In the morning you need to avoid bright light for a few hours to keep the clock from being yet again set to an earlier time.

You can also use this approach in preparation for westward travel (e.g., from London to New York) to set your clock back a few time zones and avoid jet lag.

If you are too much of a night owl, i.e., you tend to fall asleep too late at night, you need to avoid light in the evening and bathe in light early in the morning. Most of us, however, don’t just want to hang out in the dark and not use our TV, phone, and computer.

Orange and red light don’t influence our clock much. Wearing well-designed blue-blocking glasses at night for two to three hours before bedtime allows you to filter out the clock-delaying wavelengths.

In the morning then, you expose yourself to bright sunlight or use bright white light or blue/blue-green light to set your clock to an earlier time (advance it).

The same applies to eastward travel (e.g., from New York to London), where you want to advance your clock a few time zones.

Researchers in Australia have designed a calculator and glasses to apply the correct light dose to change your clock

Flinders University have spun off a company that has come up with a device called Re-timer. Re-timer is essentially a pair of light therapy glasses with built-in glue-green LEDs that can be worn to reset the biological clock.

A Belgian company, also a university spinoff, has also designed a pair of interesting light therapy glasses, Luminette, together with an app to set your schedule. More on these light therapy devices and what I have used below.

Back to the calculator: Flinders have done research into how you can estimate the most effective time for light exposure from your current sleep schedule.

They offer a sleep calculator that takes the current time you fall asleep and your current wake-up time as inputs. These parameters are used to approximate your internal biological clock time. You feed the calculator with your desired sleep or wake-up time, and it returns a 7-day schedule for timed light exposure to readjust the clock to the desired time.

They also offer a jet lag calculator that takes your bed and wake up times, the current date and location and the date and city you are flying to as inputs. It then calculates a light treatment schedule.

How I used the sleep calculator and blue light to set my clock to a later sleep and wake-up time

I mentioned earlier that I often move from the country side to the city.

At the beginning of this month, I again found myself feeling sleepy early in the evening and waking up at 4:30 am to 5 am, not being able to fall back asleep.

Despite the urge to sleep earlier, I followed my desires and went to bed at 11:30 pm or later every night, and after two weeks felt really sleep deprived and tired.

I fed Flinders’ sleep calculator and it came back with a schedule:

Desired wake up time: 6:30 am

Current wake up time: 4:30 am

Fall asleep at: 11:30 pm

“The information you have entered indicates an advanced sleep rhythm.

Advanced sleep rhythms are characterized by early evening sleepiness or an inability to remain awake until bedtime.”

“The objective of wearing Re-Timer in this situation is to move sleep time later into the evening.”

The calculator suggests wearing Re-timer as follows for between 30 and 50 minutes:

Date Time
04 Feb 2018 10:30 pm
05 Feb 2018 11:00 pm
06 Feb 2018 11:30 pm
07 Feb 2018 12:00 am
08 Feb 2018 12:30 am
09 Feb 2018 1:00 am
10 Feb 2018 1:30 am

One week of evening blue-light exposure

I already had the Philips goLITE BLU, a blue light therapy device that offers a similar light intensity with its peak at a slightly lower wave-length (475 – 480 nm, right in the blue light range), so I used this device instead of Re-timer.

GoLite’s light should be as effective, if not more so, as its peak corresponds with the maximum sensitivity of the clock-setting photoreceptors at the back of the retina.

So, every night at the prescribed time, I placed GoLite on my computer desk at about half a meter from my eyes and used it for 40 minutes while browsing the news.

The protocol was easy to follow until the last three days. From 8 Feb to 10 Feb, I felt really sleepy and had to force myself to stay awake. Nevertheless, I pushed through.

Re-timer’s ebook also advises to avoid morning light, e.g., by wearing sun glasses.

Consequently, I started wearing blue-light blocking glasses in the morning from the time I woke up until about 9 am. This is to keep the early morning light from advancing my biological clock again.

Note that I also wore the glasses whenever I had to use light (e.g., for going to the bathroom) or my smartphone after bed time.

As mentioned above, if you are a night owl who wants to be able to fall asleep earlier at night, you need to use light therapy in the morning and wear blue blocking glasses in the evening. Just feed the calculator to get your personal schedule.

So what are the preliminary results of evening light exposure (as of 24 February)?

The first couple of days after the experiment, I felt sleep-deprived and jet-lagged. This jet lag has now subsided.

I start feeling sleepy about 90 minutes later than at the beginning of the experiment. To me, this is an indication that I have indeed been able to set my biological clock to a later time.

I still quite often wake up too early for my taste (e.g., 5 am, 4:30 am, 6 am), but the times have become more variable; what’s more, I am now usually able to fall back asleep faster. I really hope to get more consistency though.

I tracked my sleep parameters with a Fitbit Charge 2, which I recently got while on a trip to Hong Kong. The Fitbit Charge 2 uses an accelerometer and a heart rate sensor (heart rate variability) to determine the sleep times and sleep stages.

According to the Charge 2 my total sleep time increased:

Week of Feb 4th: 6 hrs, 0 mins avg (week of the experiment)

Week of Feb 11th: 6 hrs, 20 mins avg

Week of Feb 18th: 6 hrs, 44 mins avg

I only bought my Fitbit in the beginning of February, so, unfortunately, I don’t have enough data from before the start of the experiment.

Here is my sleep chart for 20 February, one of the above-average days (time asleep was 7 hrs 19 mins):

Sleep diagram and sleep stages for 20 FebruaryThe sleep chart for 22 February, the worst day this week (time asleep: 5 hrs 51 mins):

Sleep diagram for 22 FebruarySummary:

As I mentioned, the best indicator for me that I have indeed been able to set my clock to a later time is that I now feel sleepy about 90 minutes later than before the experiment.

My total sleep time has also improved, but it is too early to see how that will continue in the future. I still wake up quite frequently during the night, but at least I am able to fall back asleep easier.

This wasn’t a strictly controlled experiment. I wanted this to be as realistic as possible, enjoy the city life, and not restrict myself too much to perform a sleep study. I also hit the pubs and had a few beers most evenings, and I didn’t always eat at the same time.

Which light therapy device to use for setting your biological clock and optimizing sleep?

Looking at the specs, I believe Philips’ GoLite (blue light with a peak at 475 – 480 nm) should be as effective as Re-timer.

I simply used what I already had. If you already have a light therapy device, I suggest you try that in conjunction with the calculators described above.

GoLite works great, if you want to use light therapy while sitting, e.g., while working at your computer or reading a book. It has a rechargeable battery which allows for up to 60 minutes of cordless light therapy, but can also be directly powered using the included power supply. Two people could even use it at the same time, provided they sit next to each other.

Still, for mobility reasons, I will likely also get either Flinder’s Re-timer light therapy glasses or Luminette, similar glasses designed by Belgian company Lucimed.

Luminette is the brainchild of researchers from the University of Liège in Belgium.

Re-timer uses blue-green light (at around 500 nm), while Luminette exposes you to white light enhanced with blue light (peak at 468 nm).

All three light therapy device manufacturers state that their device is as effective as a 10000 lux white light lamp.

The idea of using light therapy anytime anywhere, including while doing housework, exercising, or traveling on a plane or a train is very appealing to me, and for this, glasses are just more practical.

I also plan to experiment with bright light during the day to increase my alertness. This might come in handy as a natural stimulant and to cut down on coffee.

Sunshine is the ultimate bright light treatment and “clock re-trainer.” But what does one do in its absence during the dark winter months or when working in an office with sub-optimal lighting in New York or in a tiny apartment in Hong Kong?


Personally, I feel I would serve my health best by going to sleep when I am naturally inclined to and sleep for 7 or 8 hours.

Often, however, I can’t – and sometimes I don’t want to.

I quite frequently travel across time zones, and I also alternate between country side and city.

I want to enjoy the riches each place has to offer without compromising too much on mental performance and health. I am going to continue to explore bright light therapy and see where this takes me. Stay tuned.

I suggest you also read How to Block Blue Light for Better Sleep and Why It Works.

If you are bothered by noise during sleep, you may find Choosing and Using the Ideal White Noise Machine for Sleep and How to Block out Snoring Noise useful.


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