Light and Health

Applications of light in the non-clinical environment


Adolescents are generally characterized as late chronotypes. Late chronotypes go to bed late and wake up late. It is not only their sleep timing that is shifted to a later time (as compared to early or intermediate chronotypes) but also their whole rhythms in physiology and cognitive performance are shifted. This change in the sleep-wake cycle is not only observed in humans, but is also observed in many animal species (Hagenauer & Lee 2013). So, although partly the consequence of life style, the change in sleep timing in adolescents is most likely also the result of biological changes in sleep regulation.

Nonetheless, adolescents are asked to be awake early to go to school and to be able to perform at, considering their own internal time, a non-optimal time. A study comparing grades of different chronotypes in high school students showed that late chronotypes have on average lower grades. During the early morning hours grades of early types are better than grades of late types, while this difference is not observed with exams in the late morning/early afternoon (Haraszti et al 2014, Van der Vinne et al 2014).

Light in the morning at the appropriate time can be used to shift late chronotypes to an earlier phase allowing them to a certain extent to perform better under standard social constraints (Geerdink et al, 2016). Light levels in the evening should be as low as possible to prevent a counteracting effect. In addition, a special warning is to prevent exposure to brightly lit LED screens of computer, tablet and smartphone. These devices emit a relatively large amount of blue light for that time of day and exposure to these levels results in a higher alertness, a suppression of melatonin and a delay in sleep (Cajochen et al 2011, Lemola et al 2015). Moreover, higher, probably more bluish, light levels during the day could be used to acutely enhance alertness and performance (Rüger et al 2006). Another solution is to adapt the timing of the environment; for instance in adolescents to shift school times or at least the timing of exams. Recent experiments have reported positive results of shifting school times (Boergers et al 2014, Kelley et al 2015).




Ageing is associated with wisdom but unfortunately also accompanied by physical and mental decline.  In relation to light, the decay of the ocular system like the yellowing and decreased rigidity of the lens, the increased opacity of lens (also known as cataract) negatively influences the visual performance; it becomes more difficult to focus on close distances, the distinction of colors becomes more problematic; more light is needed to perform the same visual tasks as younger people. Due to the opacity of the lens, more light is being absorbed and scattered causing a greater sensitivity to glare (the contrast between a very bright light source and its environment).  Good lighting can help elderly people to perform daily tasks (Aarts and Westerlaken, 2005;De Lepeleire et al., 2007), enhancing their independence. Sufficient light in the living area can prevent elderly people from stumbling over for example an electricity wire or a carpet.

Next to the decline of the optical system also the neurological system is subject to change in the form of less photosensitive (ganglion) cells and a degeneration of the SCN. These changes affect the non-image-forming systems resulting in a disturbed circadian rhythm which relates to sleep ((Someren E.J.W.van, 2000). When in a cataract surgeon, the yellowed lens is being replaced by a transparent one the timing of sleep is being influenced (Giménez et al 2016). Surprisingly enough the effect is not as big as expected probably due to the adaptation of the system (Giménez et al., 2014). Good lighting to support normal visual tasks and keeping the circadian system entrained by light exposure for example by going outdoors on a daily basis is currently the best advice to be given to enhance the independency.



School performance depends on various aspects such as the children- and teacher characteristics as well as the school environment. In a meta-analysis, a clear association has been found between sleep duration and cognitive performance in school-age children (8-12 years): insufficient sleep in children is associated with deficits in higher-order and complex cognitive functions and an increase in behavioral problems (Astill et al 2012). Considering the environment, school lighting is a major environmental aspect. Appropriate school lighting is critical for supporting children’s’ visual skills as well as cognitive functioning and new attempts to improve light seem to be successful (Mott et al 2012).

Environmental light levels in schools become even more important in high schools, since adolescents tend to become more late chronotypes. By applying the appropriate light at the appropriate time, both acute effects promoting alertness and entrainment of the sleep-wake rhythm will improve daytime performance.


Office buildings

Since the introduction of electric lighting, a large part of the population is spending time inside buildings during daytime. Office employees spend most of their waking time inside the buildings in which they work (i.e., Schweizer et al., 2007). To the extent that environmental conditions influence health and well-being, workplace conditions are important contributors.  While the results of nighttime studies may be relevant to night-shift work situations, the potential for dynamic blue-enriched lighting with high illuminance levels to be used to improve alertness and performance levels during daytime is also studied. Studies investigating acute alerting effects of light on human behavior and physiology during daytime have demonstrated beneficial effects of high illuminance levels or monochromatic blue light exposure  (i.e., Smolders et al., 2013; Phipps-Nelson et al 2003, Rüger et al 2006). A study by Cheung et al., (2013) and Boubekri et al., (2014) demonstrated a strong relationship between workplace (dynamic) daylight exposure and office workers' (self-reported) sleep, activity, and quality of life. Compared to workers in offices without windows, those with windows in the workplace received a much higher white light exposure during work hours.  Not only the quality of (day)light, but also the view from a window can affect an employee’s well-being. Results by Aries et al (2013) show that window views, which that are rated as being more attractive, are beneficial to building occupants by reducing discomfort. Additionally, the results showed that reduced discomfort at work can improve sleep quality, indicating that physical conditions at work influence home life.

Travelling – jet lag

Rapid transmeridian traveling leads to misalignment between the individual’s internal timing and the new destination’s external timing. This may lead to discomfort commonly known as jet lag. Examples of such discomfort are sleepiness, irritability and impaired performance (Boulos et al., 1995). The long term effects of frequent rapid transmeridian traveling have not yet been fully described, but they seem to range from cognitive defects (Cho, 2001), to metabolic disturbances (Rüger & Scheer 2009). The severity of the jet lag symptoms depends on the number of time zone crossed and on –so far unknown- individual differences. The larger the number of time zones that are crossed, the more severe de misalignment is. Given the nature of human’s circadian system (on average a period of the biological clock that is longer than 24 hours), delays are more easily achieved (faster) than advances in most individuals. Hence, flying west leads to less bad jet lag symptoms than flying east in most cases.

Light could be used to realign the individual’s internal timing with the new light/dark cycle of the destination. Light in the early biological morning can advance the internal timing, while light in the late evening will lead to a delay (Khalsa et al., 2003). Appropriate timing of light and dark (!) exposure is critical to achieve the desired results. Lighting protocols should consider the destination (time zones travelled), length of staying and whether adjusting to the destination’s time zone should occur before traveling already (Revell & Eastman, 2005). Although the hypotheses of the effects of light therapy to prevent or to cure jet lag are clear and laboratory experiments and anecdotic information support the effectiveness, large-scale well controlled experimental field studies of light therapy on jet lag symptoms are lacking (Atkinson et al 2014).

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