The explosion in technological devices within our homes over recent years, along with the recent Covid-19 pandemic has resulted in a marked increase in the use of ‘screen time’ within the home. The Catch 22 of the benefits of remote working, online education resources and mobile entertainment devices (Tablets, Games consoles etc.), with the associated potential issues with vison and sleep, mean the decision over how to manage screen time is a hard one.
This article isn’t about screen time and whether we should engage with it or not. An emotive issue in hard, anxious time times. Simply, the article is intended to provide an explanation of the benefits and disadvantages bright light exposure and why managing exposure to light at certain parts of the day is important in terms of our sleep.
Light wavelengths
It’s probably pertinent to talk a bit about light and wavelengths before we delve into the benefits or disadvantages of light and our sleep health.
Light acts on the body by two pathways. Firstly, what you can see and therefore do as a result (visual perception and responses/reflexes) are governed by the primary optic tract. Secondly, the retino-hypothalamic tract governs our circadian, endocrine (hormones), and neural-behavioural functions (nervous system and behaviour). It is this tract which is most sensitive to light (Holzman, 2010) and can have an impact on our sleep.
Visible light has many wavelengths to it (measured in nanometres) and is comprised of a spectrum of different colours (remember the prism of light from your school physics lesson?). It is our brain that tells us that visible light is white. Although other colours in the white light spectrum (400-700 nm) can be detected by cells in our retina (the light sensitive tissue layer of our eye). One in particular, is blue light wavelengths (450-495 nm) which can play a part in affecting our overall sleep health.
Rhythms and light
I’ve written before on how our bodies rely on routine and the fact that having regular synchronicity to our day is important not only for our physical, but also our mental wellbeing (And the beat goes on). The reason being is in our brain.
All humans have a natural, intrinsic rhythm. A circadian rhythm. Essentially it is a recurring cycle over 24 hours which governs our body’s need to maintain balance (homeostasis). It regulates all our biological and physiological processes such as digestive activity, body temperature, physical activity, alertness, hormone levels, immune function and perhaps most critically, sleep. It also helps our bodies respond and adapt to any environmental changes. It is the sleep rhythm that is so important to consider as it significantly impacts on all areas of our physical and mental health.
Our sleep/wake rhythm that is inextricably linked to the light/dark cycle. Previously it was thought that humans were insensitive to light and that the light dark cycle had little to do with our biological rhythms. However, it became widely accepted that cells in the eye (photoreceptors) were sensitive to light and dark and ultimately communicated with areas in the brain to inform us if it was night or daytime and therefore, time to go to sleep or wake up.
This process of informing the body of a sleep or wake state involves a complex interaction of photic (light) information which passes from the retina, through the aforementioned retino-hypothalamic tract, deep into an area of the brain, called the hypothalamus. This houses the governor of our circadian rhythms, the Suprachiasmic Nucleus (SCN) and it is this which communicates to other areas of the brain to start the process to fall asleep or remain alert and awake.
A fundamental part of this communication is the SCN’s message to the pineal gland to release Melatonin, a sleep inducing hormone, typically referred to as the vampire hormone as it only comes out at night. Melatonin is key to the onset of sleep and the suppression of which, through light, is a contributing factor to poor sleep health.
The complex interaction between our sleep/wake and light/dark cycles means the light/dark cycle entrains our circadian rhythm for sleep and if this is skewed our body homeostasis (balance) is disrupted. This can cause significant issues, particularly in relation to sleep, the impact of which is relative to how desynchronised our light dark cycle has become e.g. time zone shifts, circadian rhythm disorder or shift work.
So we can see how daylight is crucial to our daily rhythmic routine and our night time sleep. Light is effectively the ‘sleep robber’ given its effect on melatonin release. During daylight, bright light helps our alertness as it sends signals to the SCN that daylight is abundant and thus melatonin is suppressed. We remain alert and awake until night time ensues and melatonin is stimulated once more.
Light and health
Stimulation from certain wavelengths of light helps us stay alert, whether this comes from a natural source like the sun, or from electronic devices that emit blue light (e.g. screens). Through the mechanism of suppressing melatonin, bright light can have a therapeutic effect in certain disorders. For example, commonly experienced in the winter months are feelings of low mood and lethargy which is partly related to sleep and the light/dark cycle and the fact that during the winter months, days are shorter and daylight can be rather dull. As melatonin levels remain elevated with the relatively darker days, associated serotonin levels (a mood regulator) are suppressed and we are more susceptible to gloomy feelings. In extreme cases this can be related to Seasonal Affective Disorder (SAD), a pattern of recurrent significant depressive episodes that most commonly occur during the seasons of autumn or winter and reduce as spring arrives. Symptoms vary but usually include a persistent low mood, a loss of pleasure or interest in normal everyday activities, irritability and sleeping for longer than normal and finding it hard to get up in the morning. Feelings are more pronounced than occasional ‘winter blues’ with the prevalence of SAD ranging from 1.5 % to 9 %, depending on latitude (Nussbaumer-Streit et al., 2019).
The good news is, regular exposure of daylight, particularly morning light, even for just 15-30 minutes a day, is enough to lift our mood and help our sleep/wake balance, improve focus and attention and ultimately boost overall health and wellbeing. It is here where light therapy (phototherapy) has come to the forefront.
Light box therapy, or phototherapy, relates to an intervention to help certain sleep disorders through exposure to light of a particular illumination (brightness is measured in ‘Lux’). Light therapy is most effective when you have the proper combination of light intensity, duration and timing, which ultimately are dependent on the disorder being treated, but usually first thing in the morning is best with consistent use until symptoms subside.
How light box therapy works is that light, imitating outdoor light, is delivered through a fixed light box or, more directly, through light glasses. Glasses offer a suitable alternative due to the length of exposure required to reap the benefits of light therapy (typically 30-60 minutes). Due to the direct nature of the light glasses on the eye, the intensity of the light will be slightly less.
Benefits of light therapy may broadly include improved sleepiness, enhanced vigilance and cognition, improved mood and consequently a reduced risk of accidents (Comtet et al, 2019). To be safe and assured that you have the correct protocol for effective treatment (i.e. brightness (intensity), timing, duration, type of light), you should seek medical advice before attempting light therapy and always follow medical recommendations and manufacturers guidelines.
Note that there are some risks associated with light therapy for certain individuals so it can require careful management and therefore medical input. If you suspect you are suffering from SAD, also seek medical advice as medications or other alternative therapies can be prescribed e.g. cognitive behavioural therapy.
Light blocking
While the stimulation from light is helpful during the day, at night it can interfere with sleep through the suppression of melatonin (Corliss, 2021). This is where screen time becomes a problem for sleep health and evening use of items such as televisions, laptops, phones, etc. can be harmful to our sleep.
Emerging studies have investigated the effects of blue light blocking glasses in the hope these will reduce the negative effects of blue light on sleep health. However studies to date lack sufficient detail and are inconclusive. Added to this, is the fact that there is little to no standardisation of the commercially available products to block blue light, so you cannot conclusively know which wavelengths are being blocked, nor whether this affects only visual function, or nonvisual functions, such as alertness and your circadian rhythm (Corliss, 2021).
Current advice to block the stimulating blue light seems to focus on limiting screen time after dusk, particularly in the 2-3 hour window pre-bedtime. Leave your phone in another room, avoid TVs in the bedroom or try certain computer software to reduce the amount of blue light emitted e.g. Apple’s Night Shift function. Not only good for reducing the impact on sleep, but also for potential issues in eye strain. The American Academy of Ophthalmology advise using the ‘20-20-20 rule’, which is every 20 minutes look away from your screen, at an object approximately 20 feet away, for approximately 20 seconds.
Avoiding screens in a technological age is probably futile. However, addressing the amount of exposure to screens that you have, particularly later in the day is worth considering for your sleep health and ultimately your eyesight too. Not to mention the fact that using screens may induce anxiety e.g. hearing/reading bad news, and negate decreasing your brain’s arousal state pre-sleep.
Overall, with regards to light and sleep, in daytime hours try and get as much daylight as possible as this has many health benefits. Also, address any additional issues affecting your sleep e.g. noise, routine etc. More info on good sleep health strategies can be found in another of my articles here.
Happy sleeping!
References
Holman, D. C., (2010), Environmental Health Perspectives , 18(1)
Corliss, J., (2021), Can blue light blocking glasses improve your sleep? Harvard Heart Letter.
Nussbaumer‐Streit B., Forneris C. A., Morgan L. C., Van Noord M. G., Gaynes B. N., Greenblatt A., Wipplinger J., Lux L. J., Winkler D. & Gartlehner G. (2019), Light therapy for preventing seasonal affective disorder. Cochrane Database of Systematic Reviews (3)