Community//

Sleep Lightly

How Light Helps — and Hurts — Our Essential Need to Sleep

Image by Gerhard Schmolke

Can something as simple as sleep be worth millions of dollars?

Ask coaches in the National Basketball Association, whose players (all of whom — with the exception of some rookies — have million-dollar contracts) need to be at peak physical readiness while playing as many as four games in five nights and zipping in and out of multiple time zones on wearying flights. One much-buzzed-about study by Stanford University found that increased sleep can lead to increased statistical production, which translates into wins, success and revenue.

Can insufficient sleep lead to poor decision making?

Ask researchers Down Under, who conducted a study that found that lack of sleep can create impairments similar to those brought on by alcohol intoxication. In fact, subjects in the study who went 17–19 hours without sleep were as impaired as a person who had a blood-alcohol concentration (BAC) level of 0.05 percent.

Can lack of sleep put you and others in peril?

Ask the US Navy. After an alarming number of accidents — including some fatalities — the Navy noticed that some of these incidents could have been prevented if the crew involved had simply had more sleep. This past September, the US Navy issued a proclamation that fleet officers “will be required to implement watch schedules and shipboard routines that better sync with Circadian rhythms and natural sleep cycles.”

Circadian rhythms? What are those?

According to the USA’s National Institute of Health, Circadian rhythms are “physical, mental, and behavioral changes that follow a daily cycle. They respond primarily to light and darkness in an organism’s environment. Sleeping at night and being awake during the day is an example of a light-related Circadian rhythm.”

Now we’re getting somewhere: Light

It all seems so obvious: Humans need plenty of light during the daytime, and darkness at night.

Research has shown that the variation of light is by far the most important factor in setting and maintaining our natural daily rhythm — yes, that Circadian rhythm. We should be exposed to intense light in the daytime and preferably sleep in complete darkness at night. Outdoor daily light exposure will have a significant effect on maintaining our Circadian rhythms, but the reality is that we spend about 90% of our time indoors; in our homes (2/3 of this time), workplaces, schools, and public spaces. A consequence of this is that many people are exposed to very low light doses for long periods of the year — particularly now in winter, when the days are significantly shorter. Preliminary evidence suggests that low light exposure is associated with diminished health and well-being and can lead to reduced sleep quality, depressed mood, lack of energy and reduced social relations.

Or, to “quote” the International Commission on Illumination (usually abbreviated CIE for its French name, Commission internationale de l’éclairage) position statement: we need proper light at the proper time in the proper context.

Circadian Rhythms and Habits

When we sleep well — and in complete darkness — we produce the hormone melatonin; but if we are exposed to light at night, the production of melatonin is suppressed. Research has shown that exposure to even short-wave-length light — at the blue end of the spectrum — suppresses our production of melatonin.

As obvious as it seems that bedrooms should be dark at night, not everyone has curtains in their sleep chamber. These people can be affected by light coming into the room. When your bedroom is lighter than complete darkness, light is transmitted through your eyelids. (Don’t believe it? You will notice this if you close your eyes in the sunlight at the beach, for example. Or if you’re on an overnight flight and trying to sleep without an eye mask.)

Night-time outdoor lighting and indoor light sources, especially light sources with high-color temperature (“cool-white” light sources) may also have an impact on our sleep quality and natural melatonin secretion. The long-term effect of light exposure at night is not fully understood, but a number of studies indicate links to not only declines in cognitive function and work performance, but also unhealthy increases in body mass and a variety of maladies, including a possible connection between the interruption of the production of melatonin and a greater incidence of breast cancer among female workers who do shift work.

Human beings have an internal biological clock that is actually longer than 24 hours. We need adjustment every morning — a “re-set” — to “entrain” our bodies. Germans call this a zeitgeber, giving the body a re-set signal.

Sure, there are differences between so-called “morning persons” and “night persons”: morning people may have a shorter time “cycle” than 24 hours, and an extreme night person has a longer-than-average cycle. But, importantly, members of both groups still need to “re-set” in the morning by getting exposure to light, to synchronize their biological clocks to a 24-hour cycle.

Thus, it is part of a global morning ritual that, upon waking, most people open their curtains or walk into a brightly-lit room.

Seasonal Affective Disorder (SAD)

The challenges posed by light (and lack of it) pose even greater challenges as the weather gets colder and the number of daylight hours. Seasonal affective disorder (SAD), also known as winter depression or winter blues, is a form of depression that occurs more frequently in the winter months, typically arising in the autumn and disappearing in the spring. SAD will increase in incidence with increasing latitude. A milder form of seasonal mood disturbance is called sub-syndromal SAD (or S-SAD).

Typical SAD symptoms are emotional depression, lack of energy, increased need for sleep, increased irritability, increased appetite and weight gain, reduced immune-system activity and often also periodic reduced performance and productivity.

The incidence of sub-SAD is estimated to be two to three times higher than SAD. The primary treatment of winter depression is light therapy — there are special lamps on the market for the purpose. Research has also shown that exposure to daylight outdoors (~ 1000 lux) can reduce SAD symptoms; and as sub-SAD is relatively common, the amount of daylight in our homes or workplaces can be of considerable significance.

But even for those who do not suffer from SAD, it is important to regulate light intake. Here are some tips on how to best gain control of your Circadian rhythm:

  • No matter the weather, make sure to get outside and walk — even for just 30 minutes.
  • Try a digital detox at night: unplug your phone and keep it away from your bedroom. (Which in addition to removing unhealthy blue light also eliminates Pavlovian buzzes and beeps.)
  • Take necessary steps to eliminate light sources from your bedroom at night — whether with curtains over windows or by unplugging or removing other electronic devices that emit strong light.
  • Conversely, upon waking, allow plenty of light into your bedroom or dayroom, and soak it in to re-set your Circadian body clock.

As a general rule, remember to let there be light — just not too much, and at the right time.

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