"I believe that light is medicine," says clinical psychologist Dr Michael Breus, a Fellow of The American Academy of Sleep Medicine.
“Light affects our bodies in very unique and interesting ways. There is research to support how light affects disease processes, like Alzheimer’s or Parkinson’s, and mental processes like depression and anxiety, and even sexual processes like libido. You would be shocked at how many different processes light actually affects.”
So why would sleep be any different? Up until at least a decade ago, the principle source of blue light in our lives was TV screens, but now the light is near-omnipresent, from what Breus calls “close screens” – typically within about two feet of your eye.
These include tablets (but not dedicated e-readers or kindles: e-ink devices without a backlit screen), smartphones and laptops, many of which we take to bed with us each night, and which should be put away at least one hour before bedtime.
Blue light specifically activates a pigment called melanopsin in the retina, which has a major influence on the clock mechanism and melatonin secretion: too much blue light in the evening tricks the circadian clock into believing it is daytime outside.
"When it's dark, melatonin is secreted from a gland in the body with the aim of regulating our body's natural 24-hour cycle, including our sleep pattern," says dietician Orla Walsh.
“This is why it’s important to stay away from your laptop or phone before bed, as blue light for two hours before bed can reduce melatonin by 22 per cent.”
Prof Christian Cajochen agrees with the two-hour turn-off before bedtime. Head of the Centre for Chronobiology at the University of Basel, he says 12 years ago new sensors in the eye ("intrinsic photosensitive ganglion cells") were discovered, which transmit light information from the outside world directly to the brain's circadian clock.
“Interestingly, these receptors absorb light in the blue range. That’s why our circadian sleep-wake pattern responds very sensitively to blue light. In other words, when we ‘see’ the light, it not only affects our vision but also our non-visual body clock.”
Various sleep apps, which use a motion-tracker and/or a sound-recorder, claim to tap into those circadian rhythms, by apparently monitoring sleep patterns. A “smart alarm” will then wake you in a light sleep cycle that is nearest your ideal wake time.
These apps generally fall into two standard forms: fitness trackers that have sleep-tracking capabilities (typically involving a wearable sensor or wristband that tracks your body movements as you sleep) or smartphone apps that use an accelerometer built to record your movements.
But your body movements do not necessarily reflect sleep stages, while a phone next to or beneath your bed can be even less accurate – especially if you don’t sleep alone. So, does Cajochen consider them as a gimmick or genuine aid?
“I would say a gimmick which works amazingly well. Some people like it while some people complain of not getting enough sleep, because they are awoken by the device too early. At least they raise awareness of how important sleep is and that sleep is composed of different cycles.”
But it’s in reducing blue light exposure that apps appear to be more effective in producing better sleep, though there is still room for improvement in eliminating blue light without compromising the light colour temperature of the screen.
Many experts suggest downloading the f.lux app (https://justgetflux.com/- it works on windows and macs alike) for computers and mobile devices, or switching to nightshift mode in iPhone since the release of iOS 9.3 earlier this year.
Research suggests that teenagers may be getting the brunt of blue light, since their optic lenses (and therefore light perception) are clearer than in adults.
"What I'm really concerned about are adolescents," says Sigird Veasey, professor of medicine at the Centre for Sleep and Circadian Neurobiology at the Perelman School of Medicine at the University of Pennsylvania.
“It really is unchartered waters, from a research perspective, to have all these adolescents going to bed with tablets and smart phones . . . I think we are heading towards some serious problems with not only neural injury but with chronic mood disturbances as well. All of these wake-active neurons play a really vital role in mood and, if injured, will likely predispose them to depression.”
“What we really need to do is set-up 15- or 20-year studies . . . You’d really have to look at it long-term to see how it’s affecting their sleep and brain functions down the road. Right now, nobody is doing these studies.”
Cajochen says the impact of sleep deprivation on human health is “scarcely investigated”.
“However, short or mid-term effects of chronic sleep loss are manifold and affect the emotional level, such as stress or depression; the cognitive level, such as impaired attention and memory, as well as the somatic level, with a higher risk for diabetes and cardiovascular problems.”
According to Prof Paul Reading, a neurology consultant at the Sleep Clinic at James Cook University Hospital in Middlesbrough, chronic sleep deprivation may well predispose you to cardiovascular disease, diabetes, cancer and even early death.
Sleep quality and dreaming
“A dream is a mental manifestation of some type of information processing,” says Breus.
“Eighty percent of the time when you wake someone up from REM sleep they say they are dreaming.”
Breus says REM sleep is when you move information from your short-term memory to your long-term memory, where you are able to recall that information whenever you are looking for it, which, he says, is what dreaming most likely represents.
“I don’t think dreams are a good metric for the depth or quality of our sleep: some people say when they dream a lot they don’t feel well-rested, while others say ‘I’m sleeping better now and I’m dreaming.’ I think that is more of a perception than a reality.”
“We actually dream in any sleep state including deep slow-wave sleep,” says Cajochen.
“However, the chance to dream is much higher during REM sleep. How dreaming affects our sleep quality is still a mystery. Bad dreams of course can be very disturbing. Luckily we do not remember most of our dreams consciously.”