Few people understand the profound effect light has on our health.
I’ve worked a rotating shift schedule for over ten years. And sure, I’ve always known that night shifts and the flip flopping schedule aren’t good for my health, but, until recently, I hadn’t given much thought as to the underlying cause.
As I’m always looking for ways to lead a healthier life – despite my shift schedule – I spend an enormous amount of time reading scientific papers. Anything related to shift work and circadian biology gets the bulk of my attention.
If there’s a common thread among the papers I’ve read, it is this: artificial light at night is bad.
In this article, we’ll explore what light is, how it affects our health and circadian rhythms, and strategies for limiting exposure to artificial light at night (ALAN).
What is light?
- Light is actually electromagnetic radiation of varying wavelengths.
- The shorter the wavelength, the more energy it contains and vice versa.
- Only wavelengths from about 380 to 740 nanometers (nm) are visible to the human eye.
- We see this light as different colours depending on the wavelength (remember ROY G BIV from school). When seen all together, these wavelengths produce “white light”.
What is blue light? And what is all the fuss about?
Until fairly recently, blue light hasn’t posed much of a problem. Humans have evolved over thousands of years under the lighting conditions imposed by the rise and fall of the sun. Any light required after nightfall was provided by fire or candlelight; which emit very little in the way of blue light. But thanks to modern technology and a twenty-four hour society, our exposure to blue light has increased dramatically.
Most newer lighting technologies emit far more blue light, not only compared to candlelight, but also to older tech like incandescent lighting.
The problem is that our eyes, and, as you’ll see in this post, our circadian rhythms, are most sensitive to wavelengths in the blue spectrum: generally considered as the 400 to 495 nm range.
Sources of blue light
The sun is the main source of blue light, but there are many man-made sources, including: light-emitting diode (LED), fluorescent, compact-fluorescent light (CFL), incandescent and halogen. These artificial light sources emit varying amounts of blue light.
Unfortunately, the lights that are most energy efficient also tend to be the most disruptive.
Aside from lights, the displays on our digital devices are typically LED and are also significant sources of blue light.
Not only has our artificial light become much more blue dominant, but the amount of people working outside normal daylight hours is on the rise. Twenty-four-hour access to goods and services has become the norm.
Shift workers aside, many others are following similarly abnormal schedules. Fuelled by the internet, round-the-clock information and entertainment is a temptation that was absent only a couple decades ago.
How blue light affects the eye and our circadian rhythms
You may remember rod and cone cells from highschool, but there is a third category of cells that plays a largely non-image-forming role; intrinsically photosensitive retinal ganglion cells (ipRGCs). One of these roles is circadian entrainment.1
Lighting changes are detected by a light-sensing protein, in the ipRGCs, called melanopsin, and this information is relayed directly to the suprachiasmatic nucleus (SCN) via optic fibres.
Click here for more information on the SCN and circadian rhythms.
Because of the SCN’s central role in circadian biology, it is often referred to as the master clock. Virtually every cell in the human body follows a circadian rhythm, and the SCN plays a role in synchronizing and coordinating these rhythms.
As light is the primary cue for synchronizing the SCN with the external environment, maintaining light exposure in accordance with the natural light-dark cycle is priority number one for healthy rhythms.
The impact light has on our rhythms is a function of intensity (lux), spectrum (nm), the angle at which it hits the eye, the duration and pattern of exposure, previous lighting history, and the timing of light exposure.
Below, we will explore how each of these qualities affects our circadian rhythms through their impact on melatonin. The measurement of melatonin, a hormone that signals to the body that it’s time for sleep, is a well-established proxy of circadian timing.
Brightness, or light intensity (lux)
Melatonin suppression occurs even with light levels as low as thirty lux, delaying its release by 77 minutes on average.2 For comparison, a bedside lamp typically produces between twenty and eighty lux.
Children appear to be even more susceptible. One study showed that one hour of 1000 lux (typical in fast food restaurants, grocery/drug stores) causes about 90% melatonin suppression in young children.3
Notice that daylight has a greater effect than incandescent light for a given lux rating. This is because sunlight contains more of the blue wavelengths than incandescent lighting. Which brings us to the next variable:
Color, or wavelength (nm)
Peak melatonin suppression occurs at wavelengths of about 480 nm, which, as you may have guessed, lies in the blue portion of the spectrum. The melanopsin receptors become increasingly less sensitive the farther you move away from the peak. For example, wavelengths around 450 nm suppress melatonin about half as much as the 480 nm wavelengths.
This is why, when looking for blue-light-blocking glasses, you should look for lenses that block not only the peak, but also a significant portion beyond it. As you can see from the image above, wavelengths in the green portion of the spectrum also have a significant impact on melatonin.
Researchers investigating protection from artificial light at night typically have participants wear glasses that block everything below 530 to 540 nm.
I like BON CHARGE (Formerly BLUblox). They are proven to block 100% of wavelengths below 550 nm. But I’ll cover protective measures in more detail later in the post.
Although light intensity is an important factor, the amount of blue light appears to account for the majority of the response. A 2013 study compared a 6.7 hour exposure of white light at 10,000 lux with a 6.5 hour exposure of 480 nm light at 11.2 lux. Even though the 480 nm light was just a small fraction of the light intensity, it induced about 75% of the response of the white light.4
Duration, and pattern of light exposure
The longer you are exposed to light, the greater the melatonin suppression, and the greater the circadian phase delay. At less than two hours, you’re already half-way to maximum melatonin suppression.
But the relationship between the duration of light exposure and melatonin suppression is more complex than this. Sequences of very short light flashes can also induce large phase shifts.
For example, one study showed that six 15-minute pulses of 9500 lux white light, separated by 60 minutes of dim light, produced a similar phase-shift as a continuous 6.5 hour exposure (with only 23% of the duration).5
Even more astounding, a 45 min phase delay was obtained using sixty 2-millisecond pulses (for just 0.12 seconds total duration) of 473 lux of white light separated by 60 seconds of darkness from 02:00 to 03:00.6
The angle at which light hits the eye
Interestingly, the angle of the incoming light also plays a role.
A 2003 study determined that light hitting the eye from above (light falls on inferior retinal field) is more effective in suppressing melatonin than light coming from below eye level (light falling on superior retinal field). In fact, the effect of superior retinal exposure was not significantly different from that of the dark control condition.7
Prior light exposure
Not only does light intensity matter, but the difference between light intensities also plays a role.
Exposure to bright light in the morning reduces circadian phase shifts in response to evening light.8 If you spend all day indoors, you will be more sensitive to ALAN, and will experience greater melatonin suppression.
Time of exposure
Timing is everything when it comes to the effect light has on us.
Bright, blue light, is beneficial to us during the day. It helps synchronize our clocks to the natural light-dark cycle, which is important for circadian health. Sunlight exposure also improves energy and mood, and is our primary source of vitamin D.
In fact, light therapy is used as a treatment for many conditions: seasonal affective disorder (SAD) and other types of depression, jet lag, sleep disorders, dementia, and adaptation to shift work.
But when exposed to light after nightfall, melatonin is suppressed, disrupting our sleep and shifting our circadian rhythms.
Even within the night, timing plays a key role. Light exposure during the first half of the night causes phase delays, whereas light during the latter half causes a phase advance.
Nighttime light has also been shown to increase, cortisol, heart rate and body temperature; all of which are detrimental to sleep.9
Downstream effect on health
So what does all this mean? How important is it to have healthy circadian rhythms?
Melatonin is often referred to as the sleep hormone, as it helps regulate our sleep-wake cycles. But it is not only our sleep that is impacted by ALAN.
Melatonin also plays an important role in our metabolism and our immune system. Circadian disruption and the suppression of melatonin increases your risk of many negative health conditions.
Cancer tumors grow faster when melatonin is suppressed.10 This may explain the up to 200% increase in prostate cancer and 50% increase in breast cancer for shift-working men and women respectively.11
ALAN also increases your risk of cardiovascular disease (CVD), with the greatest increases, once again, seen in shift workers (20-40%).12
Taking a step away from shift work for a moment, obesity almost doubles for people who sleep with the lights on.13
Exposure to ALAN is also associated with, aging, depression, diabetes, dementia and hypertension.
There is a lot to be concerned about, but also much we can do to reduce our risk.
How to protect yourself from artificial / blue light at night
One of the most effective ways to avoid the harmful effects of ALAN is simply to remove yourself from modern society. Camping has been shown very effective in normalizing circadian rhythms, causing people to fall asleep earlier, wake up earlier, and feel better.
In a couple of studies on this, people who camped for a week saw melatonin levels rise much earlier than non-campers. But even more notable, melatonin secretion stopped before the campers woke up. This occurred after wake-up time for the non-campers, which may explain the morning grogginess that is so rampant in our society – and our reliance on that morning cup of coffee.
I can see it now, the thousands tens of you reading this will all hurriedly gather your camping equipment and prepare for weeks of social isolation in the wilderness.
Obviously camping is not a reasonable long-term solution. Instead, we must learn to be more conscious of our environmental light – which means maximizing light exposure during the day, and limiting exposure at night.
Here are some tactics to help you do just that. Although technology has created the problem, it can also play a key role in protecting us.
Best practices for optimizing your light exposure
Expose yourself to natural sunlight during the day – the earlier the better. Aside from improving mood and wakefulness,14 significant sunlight exposure can also reduce blue light’s impact on melatonin after nightfall.15 I’m not sure what the minimum effective dose is, but ninety minutes of morning sunlight has been proven effective.16
To achieve this effect, and optimize circadian rhythms, forgo wearing sunglasses in the morning.
When required to spend time indoors, gravitate towards large windows. Sunlight coming in through the windows is brighter than typical office lighting.
Avoid bright lights and screens for two to three hours before going to bed. If running errands after nightfall, be aware that grocery stores and pharmacies can have more than 500 lux of light.
Using technology to protect yourself
Let’s face it. Most of us aren’t going to stop doing activities that require lighting after nightfall. That would leave us with significantly less time for both productivity and leisure. This is especially true during the winter months for anyone not living along the equator.
Fortunately, there are many tools we can use to regain this time, while minimizing the impact to our sleep and health. Here are some of the tools that can help:
Install apps on your devices that shift the colours of your display to the warmer end of the spectrum. Recent Mac models and iPhones have a Night Shift feature built in which can automatically alter your display from sunset to sunrise. Android has a similar feature in Night Light, and you can download f.lux for computers or devices that don’t come with preinstalled software.
Many devices in the typical bedroom emit light even when powered off. These devices should be removed from the bedroom if possible, or the offending light taped over with electrical tape or LightDims.
A light box may be a worthwhile investment for those with limited access to outdoor light. They are also beneficial at extreme latitudes that have little to no sunlight during the winter months.
If using night lights, use dim red or amber lights. Red light has the least power to shift circadian rhythms and suppress melatonin. These are also best plugged into lower outlets since light from below is significantly less effective at suppressing melatonin.
You can also purchase smart lights that can be programmed to emit the most appropriate spectrum of light according to time of day. While relatively expensive, Philips Hue is an excellent option if you decide to go this route. It’s great for those who want the whole family protected from inappropriately timed blue light, without requiring everyone to wear blue-light-blocking glasses.
Dimmable lights provide another way to lower your evening light exposure.
When working in the evening, use task lighting, such as a table lamp, so that most of the light is hitting the work surface and not your eyes. Depending on what you’re doing, a flashlight or headlamp could help as well.
Blue-light-blocking glasses
This is probably the single most effective means of protection, since proper blue-light-blocking glasses will protect you no matter what type of lighting you encounter.
As a shift worker, my lighting environment is often at odds with my internal clock. I have little control over workplace lighting and no control over the rise and fall of the sun.
Blue-light-blocking glasses help me regain some control over my light exposure. They are similarly useful for frequent fliers as a way to minimize jet-lag.
They work by filtering out the most disruptive wavelengths so our melatonin profile and circadian rhythms are preserved.
Since 480 nm wavelengths are the most disruptive, you want a lens that blocks this peak, as well as a significant portion of the wavelengths on either side of it.
Because of this, I use glasses from BON CHARGE. They have been tested to block 100% of wavelengths below 550 nm. I chose them, not only because they block more harmful light than most brands, but also because they offer a great selection of frames and are available with prescription lenses.
If you are a shift worker and want more information specific to your needs, check out Why Every Shift Worker Needs Blue-Light-Blocking Glasses
Conclusion
Exposure to artificial light at night, especially blue light, is an extremely recent problem in terms of human history. Evolution hasn’t had time to provide a solution.
But once you are aware of the dangers, it is relatively easy to protect yourself.
Featured photo by Alexander London on Unsplash
- https://www.ncbi.nlm.nih.gov/pubmed/12481141[↩]
- https://doi.org/10.1037/pnas.1901824116[↩]
- https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.13617[↩]
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3630790/[↩]
- https://www.ncbi.nlm.nih.gov/pubmed/15039146[↩]
- https://doi.org/10.1371/journal.pone.0022078[↩]
- https://doi.org/10.1177/0748730402239678[↩]
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6212492/[↩]
- https://doi.org/10.1152/ajpregu.00121.2005[↩]
- https://www.ncbi.nlm.nih.gov/pubmed/16217131[↩]
- https://circadianlight.com/images/pdfs/White%20Paper/CL_Breast_ProstateCancer_Mini.pdf[↩]
- https://circadianlight.com/images/pdfs/White%20Paper/CL_MiniWhiteCard.pdf[↩]
- https://circadianlight.com/about-us/blog/item/112-whitepaper[↩]
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3630978/[↩]
- https://www.ncbi.nlm.nih.gov/pubmed/27539026[↩]
- https://www.ncbi.nlm.nih.gov/pubmed/26777427
[↩]