This post was written by Keith Dawson for UBM Tech’s community Web site All LED Lighting, sponsored by Philips Lumileds. It is archived here for informational purposes only because the All LED Lighting site may go dark at any time. This material is Copyright 2013-2015 by UBM Americas.


LEDs & Sleep

The effects of artificial light, and LED light in particular, on our sleep patterns are being more widely discussed, thanks to Harvard Medical School researcher Dr. Charles Czeisler.

"The Nightmare" by John Henry Fuseli, 1782 (public domain)

Late in May there was a flurry of stories in the media about what the widespread use of artificial light is doing to our health. I believe I have run down the original impetus for this outbreak of coverage of what is, after all, 30-year-old news: Harvard Medical School's Dr. Charles Czeisler presented a talk at TEDx in Cambridge on May 18. This is the man who demonstrated, in 1981, that daylight keeps a person's internal clock aligned with the environment. wrote up Dr. Czeisler's warnings; Harvard Medical School published "Blue light has a dark side"; the Boston Globe did a profile; and the Huffington Post picked up the story.

Now, we have written about and chatted about and discussed these issues here over the last number of weeks. However, the recent upsurge of media interest in light, darkness, LEDs, and sleep has brought out a few new aspects of the subject.

The economics of it
One correlation that was new to me: the cost per lumen to produce artificial light has fallen through about two orders of magnitude over the last century, and as light costs less we consume more of it. "Between 1950 and 2000, for example, as the cost of light production fell sixfold, UK per capita light consumption rose fourfold," according to (High-efficacy LEDs, of course, continue and accelerate the trend towards falling cost per lumen.)

We are sleeping less. Today 30 percent of employed adults in the US say they sleep less than 6 hours in 24; among night workers, the figure tops 44 percent. Fifty years ago, only 3 percent of the population in the US slept so little.

While correlation is not causation, these trends coincide with the dramatic increases in obesity, depression, diabetes, cancer, and heart disease over the same period. These are all ills that have been associated, more or less directly, with the disruption of circadian rhythms and sleep patterns.

"We never wake up"
One fascinating sidelight in the video of Dr. Czeisler's TEDx talk is his account of visiting a remote Brazilian village that had limited access to electricity; artificial light was a luxury there. He found one dwelling that had never had artificial light. He talked with the parents of a family of 9, who all lived in the dirt-floored, one-room hut. When darkness fell they all went to sleep in that room, rising with the dawn. Dr. Czeisler asked, through a translator, what happened when one or more of the children became restless and woke in the night. It took a few tries for the parents to comprehend the question. "We never wake up during the night," was the reply. Not ever. When was the last time you or your kids slept all through a long night?

The blues
Both compact fluorescents and LED bulbs for residential use produce more blue light than the incandescents that they are displacing. Blue light is the most potent frequency for suppressing melatonin production and for shifting the body's clock forward.'s writeup notes that some commercial users of LED lighting must not have heard this news. Armed with the new ability to change the color of ambient light, "some airlines... suffuse aircraft cabins with monochromatic blue light at night, the optimal color for suppressing melatonin and disrupting sleep."

Most of us have heard the advice not to use computers or other blue-light producing electronics within a couple of hours of bedtime, so as not to affect out sleep adversely. This advice may have to be extended to lighting in general as LEDs proliferate within our homes.

Even though we can make LED lights that do not lean so heavily on the blue end of the spectrum, and in some cases can set the color of their light output, there is a lot of industry momentum to overcome and human habit to reform if we are regain the synchrony with the daily rhythms of nature that is our birthright.

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