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I've heard claimed many times that reading an iPad in bed makes for worse sleep quality than reading a book or a Kindle with a bedside lamp,

Possible explanations I've heard are because of the brightness level, the blue-rich light or the angle of lighting.

Looking on wikipedia probably raised more questions than settled:

A 2012 study [...] showed that melatonin levels are suppressed by roughly 22% when someone is exposed to backlit screens for two hours.

However there is no effect for less than two hours at full brightness, which is clearly not how I would typically use an iPad before falling asleep:

The tablets were then turned on, with their displays at full brightness. The conclusions from the study were that with only one hour of use, there was no significant melatonin suppression. However, two hours of use did lead to significant melatonin suppression.

--http://en.wikipedia.org/wiki/Electronic_media_and_sleep#Self-luminous_tablets

The study had only 13 test subjects and no double blind, so I'm quite doubtful it can give a reliable answer anyways.

What does the science say? Should I go back and read my Kindle or can I enjoy my iPad without fear of screwing up my sleep patterns?

  • related: skeptics.stackexchange.com/questions/9024/… – Sklivvz Jan 7 '14 at 20:45
  • These findings mey be somewhat biased, unless they explicitly compared Kindles with iPad when the latter was using night-mode readers (turning text into white-on-black-background). – user5341 Jan 10 '14 at 17:33
  • Also, this can probably be migrated to new ebooks SE (not that it's offtopic here, but there may be better expertise there). – user5341 Jan 10 '14 at 17:34
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That Wikipedia article and several visible results from Google searches on this topic appear to draw their information from a Rensselaer Polytechnic Institute press release, http://news.rpi.edu/luwakkey/3074.

Going back to the source, it does indeed indicate that exposure to self-luminous displays for less than two hours still has an effect.

The actual melatonin suppression values after 60 minutes were very similar to those estimated using a predictive model of human circadian phototransduction for one-hour light exposures.

The reason the author provided for why this is problematic for sleep:

Melatonin is a hormone produced by the pineal gland at night and under conditions of darkness in both diurnal and nocturnal species. It is a “timing messenger,” signaling nighttime information throughout the body. Exposure to light at night, especially short-wavelength light, can slow or even cease nocturnal melatonin production. Suppression of melatonin by light at night resulting in circadian disruption has been implicated in sleep disturbances...

You rightly point out that the referenced study from RPI is quite small (limiting the statistical significance that can be inferred), however there have been many studies on the effects of artificial light over the years.

For example, an earlier report with contributions from people at the University of Connecticut, Bassett Research Institute, Jefferson Medical College, Thomas Jefferson University, the Danish Cancer Society, Harvard Medical School, the University of Virginia, the US National Institute of Environmental Health Sciences, and others in addition to Rensselaer had this to say:

Humans have evolved over millions of years and adapted to a solar day of approximately 12 hr of light and 12 hr of dark, latitude and season permitting. Our ability to artificially light the night began about 250,000 years ... However, only in the last 120 years has environmental illumination begun to change on a pervasive scale for the masses of people through the introduction of electric lighting. ... It has become apparent, however, that although of obvious benefit, it may not be completely innocuous. Light, including artificial light, can be potent in regulating human physiology and behavior and can therefore alter human physiology when inappropriately timed. One example of potential light-induced disruption is the effect of light on circadian organization, including the production of several hormone rhythms. Changes in light–dark exposure shift the timing of the circadian system such that internal rhythms can become desynchronized from both the external environment and internally with each other, impairing our ability to sleep and wake at the appropriate times and compromising metabolic processes. Light can also have direct acute effects on neuroendocrine systems, for example, in suppressing melatonin synthesis or elevating cortisol production that may have untoward long-term consequences.

In short, the accuracy of the claimed 0.18% per minute suppression of melatonin does not appear to be independently verified. Notwithstanding, the vast majority of scientific literature on this does agree that artificial light at night can adversely affect sleep.

  • 1
    Thanks, but I did not ask if light keeps you awake. I am asking if normal usage of self-lighting tablets keeps you awake more than passively lit ones (or a book, for that matter). Comparing light and darkness is not an answer :-) – Sklivvz Jan 10 '14 at 10:36
  • You asked if "reading off a self-luminous tablet impact the quality of sleep." That's what I answered. ;) Perhaps you misunderstood the sources' discussion of natural light, which only serves to explanation why self-lighting tablets can effect our sleep. – CircleSquared Jan 10 '14 at 11:00
  • The question is quite specific on the matter, though. – Sklivvz Jan 10 '14 at 11:02
  • You asked if lit devices can affect your sleep. I said yes. You expressed confusion over the explanations given on why it happens, so I elaborated. You pointed out that Wikipedia didn't clarify maters, so I went to the article's source to show that it contradicted the WP statement "that with only one hour of use, there was no significant melatonin suppression." You expressed doubt over the mentioned study's methodology and asked "what the science say[s]." I confirmed the science generally agrees that lit devices can affect your sleep. I'm not sure what I left out. :/ – CircleSquared Jan 10 '14 at 11:14
  • I am grateful of your answer, don't get me wrong. The point I am trying to convey here is that showing that light can mess up my sleep pattern is futile: whether I read a kindle, or an iPad, or a book, I am exposed to light. That part of the answer is absolutely non-specific and thus not useful in showing any difference. The first part attempts to answer my question with the wrong source: we both agree that that article is unreliable, so it doesn't really matter what it claims. I am looking for further evidence. – Sklivvz Jan 10 '14 at 11:27
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Guessing it does not count as science-related: iPads are so bad for your healthy sleep that even Apple offers now a redshifting feature in newer devices. But that is partially because: Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness:

Moreover, the observation that the endogenous circadian melatonin phase was 1.5 h later when reading an LE-eBook compared with reading from a printed book suggests that using a light-emitting device in the hours before bedtime is likely to increase the risk of delayed sleep-phase disorder and sleep onset insomnia, especially among individuals living in society who self-select their bedtimes and wake times. Induction of such misalignment of circadian phase is likely to lead to chronic sleep deficiency.

Although it also was quite a small sample: Light at night is bad, but iPads make it worse. At least as long as they emit too much blue.

The American Medical Association's Council on Science and Public Health: "recognizes that exposure to excessive light at night, including extended use of various electronic media, can disrupt sleep or exacerbate sleep disorders, especially in children and adolescents. This effect can be minimized by using dim red lighting in the nighttime bedroom environment."

Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans Joshua J. Gooley, Kyle Chamberlain, Kurt A. Smith, Sat Bir S. Khalsa, Shantha M. W. Rajaratnam, Eliza Van Reen, Jamie M. Zeitzer, Charles A. Czeisler, Steven W. Lockley J Clin Endocrinol Metab. 2011 March; 96(3): E463–E472. Published online 2010 December 30. doi: 10.1210/jc.2010-2098

Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression Jamie M Zeitzer, Derk-Jan Dijk, Richard E Kronauer, Emery N Brown, Charles A Czeisler J Physiol. 2000 August 1; 526(Pt 3): 695–702. doi: 10.1111/j.1469-7793.2000.00695.x PMCID: PMC2270041

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