How many times have you heard this refrain: “I feel groggy, I didn’t get enough sleep.”  I’ve experienced this feeling more times than I care to remember. Nowadays, it seems like life itself is incompatible with a good night’s sleep.

Sometimes it’s because of work. There was too much work taken home, you had a deadline to meet, or you had a stressful day. Sometimes it’s for fun. You couldn’t put down that riveting novel or you watched TV too late (and was mad at yourself for this total waste of time). And then there are our devices: catching up on email or Facebook. Or, reading the news or nonsense on your smartphone. All these activities (and more) seem to conspire to deprive us of sleep.

Have you ever wished that you could resign from all this modernity and lead a stress-free “natural life?” I know I have. So it made me wonder what would it be like to “go back to nature”. Would we finally be able to get a good night’s sleep?


Before candles, gaslight, and electricity

Of course, we can’t go back in time to find out how much our ancestors used to sleep. But investigators from UCLA hit on an ingenious approach. They studied three hunter-gatherer and hunter-horticulturist groups that had no access to electricity—the only source of light was the sun, the moon, and small fires.

They found these “primitive” communities in Tanzania (the Hadza group), Namibia (the Ju/’hoansi group of the San people) and Bolivia (the Tsimane’ tribe). The researchers monitored the participants’ sleep over several days or weeks using activity and light recorders.

What they found was that the average sleep duration across the three groups—the interval between sleep onset and sleep end—was 7.7 hours (see figure).

Daily patterns of sleep

Daily patterns
With permission. Dijk and Skeldon, Nature, 527, 176, 2015

The data on contemporary people’s sleep duration are obtained through self-reporting, which is a bit less reliable than the direct observations used in this study. Be that as it may, today 30% of all employed U.S. adults and 44% of night workers report averaging less than 6 hours sleep per night, whereas 50 years ago less than 3% of the U.S. adult population slept so little. Worldwide, children are sleeping about 1.2 hours less on school nights than a century ago. Most of us also sleep at different times during the week than at weekends and holidays, inducing “social jet lag”, which further disrupts circadian rhythms.


What changed?

The obvious answer is our exposure to artificial light. Hunter-gatherers were exposed only to the dim light of small fires. Ancient oil lamps and candles didn’t increase it by much if any. But then, courtesy of Mr. Thomas Edison, the invention of the incandescent bulb increased our exposure to artificial light by orders of magnitude.

It wasn’t all bad, of course. Economic activity increased by leaps and bounds, workers could spend their evenings reading newspapers, magazines, and books (imagine!) with untold benefits of creating an educated and socially aware citizenry.


The dark side of light

Because the use of traditional incandescent light bulbs to produce light accounts for 19% of electricity consumption worldwide, many governments are them phasing out. Is this another governmental intrusion in our lives? In a way, it is. But in the laudable cause of energy conservation, we are encouraged to switch our lighting to the more energy-efficient solid-state light-emitting diodes (LEDs). This trend is not limited to lighting our homes only. LED is used in televisions and computer screens, laptops, tablets and hand-held devices.


LEDs and sleep

Our eyes can perceive images, and they also sense light and dark. Surprisingly, these two seemingly related functions are totally independent of each other.

Images are perceived by two cell types in the retina—the rods and cones. There is also a lesser-known set of cells whose only function is sensitivity to light. These cells, called intrinsically photosensitive Retinal Ganglion Cells (ipRGCs).

The ipRGCs contain the photopigment melanopsin. When light strikes this pigment, it causes our pupils to involuntarily constrict. This reflex even occurs in blind people. But wait, there is more. The sensitivity to dark/light suggests that these cells might have something to do with our circadian cycle. And, indeed, they do. These cells send axons to the suprachiasmatic nucleus (SCN), which is the seat of the biological clock that orchestrates our circadian rhythm.

How is this orchestration accomplished? Like everything in our physiology, it’s through a yin/yang mechanism. Light inhibits the SCN neurons that send the pineal gland orders to secrete melatonin, the sleep-inducing hormone. But it also activates neurons that release orexin, an arousal-promoting hormone.

Now we come to the crux of the matter when it comes to our discussion of modern day life and sleep. LED light is richer in blue light than is natural light, or even incandescent lighting. And ipRGC, those light-sensitive cells, are most sensitive to blue light. Therefore, nighttime exposure to blue light results in the same neuronal reaction that occurs in daylight; melatonin release is suppressed and orexin activity is increased. On the behavioral level, this translates to interference with sleep and increase in alertness.

There is another, more sinister aspect to blue light. Together with its neighbor on the light spectrum, ultraviolet light, they can damage the retina and promote age-related macular degeneration (AMD), the leading cause of blindness in the U.S. and the rest of the industrial world. But that’s a different story (one that I may write sometime soon).


What’s to be done?

As we say in medicine, first of all, do no harm. Don’t watch TV or read your smartphone or tablet at night. Unlike book reading via an incandescent bulb that may put you to sleep (like it does to me), LED-lighted devices will keep you awake—remember it’s activating the production of orexin, the alertness hormone. So, if you want to sleep, stay away from LED light at night.

Second, get yourself a low-blue nightlight. You can find a good discussion of what’s available in this article.

And finally, a plea to our wiz technologists: You sent a man to the moon, so can’t you please insert a blue filter in our LED devices? Our well-rested brains would be ever so grateful.

Dov Michaeli, MD, PhD


  1. Very informative article. I oftentimes find that when I look at my phone for too long before bed, it is very hard to get a good nights sleep. The artificial light tricks our bodies into thinking that we should be awake. Once I started putting my phone on my desk rather than my pillow, my quality of sleep improved drastically.


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