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The effect of light on performance The parallels between astronauts and office workers
Introduction It is widely known that light has an effect on our wellbeing. In general, north Europeans suffer more from afflictions such as winter depression than central Europeans do. This disparity is explained by the number of daylight hours; in winter, a city such as Reykjavik sometimes has fewer than five hours of daylight. Light therapy is now a widely accepted intervention for promoting a positive state of mind in these northern regions. But in addition to mood, the fact that light also has an effect on our performance, is still uncharted territory for many people, let alone that employers provide an effective response.
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Astronauts, light and performance Research conducted on NASA astronauts (Flynn-Evans et al. 2016) showed that astronauts who spend any length of time in space sleep six hours a night on average (as opposed to the recommended standard minimum of seven hours). Absence of the “earthly” cycle of daylight contributes to disruption of the human biorhythm. In addition, a previous study of space shuttle astronauts showed that a change in the Circadian rhythm was accompanied by a deterioration in cognitive function. Van Dijk et al. (2001) compared cognitive performance before, during and after space travel and demonstrated that astronauts scored worse on psychomotor, memory and mathematical tasks during space travel. Researchers compared this to measurements of the Circadian rhythm and related hormone levels. They concluded that because of changes to the Circadian rhythm caused by complex lightdark cycles in space, quality of sleep was affected and cognitive performance deteriorated.
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The dynamic nature of natural light Earthly light changes in intensity and wavelength during the day in a dynamic way. This is reflected in a change in the colour of the light; whereas morning light has a bluish tone (short wavelength, high intensity), this turns red as evening approaches (longer wavelength, moderate intensity). Figure 1 The blue light of a sunrise versus the more red light of a sunset stimulates the pineal gland (epiphysis) to produce more cortisol and stimulate the production of melatonin respectively.
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This dynamic light enters through our eyes and is sent via the optic nerve to the regions of the brain responsible for hormone production. The presence of blue light (from sunlight or artificial light, televisions or monitors) stimulates the production of cortisol and inhibits the production of melatonin, the ‘sleep hormone’. Conversely, if exposure to blue light decreases, it stimulates the natural production of melatonin. This is the signal for the body to gradually relax.
Cortisol Cortisol is also known as the stress hormone. Cortisol causes protein in muscle to break down, thus releasing amino acids, which deliver energy (glucose). The production of cortisol in the body follows the Circadian rhythm– the level of production varies throughout the day. More cortisol is released in the morning than the evening
Melatonin Melatonin is also known as the sleep hormone. The production of this hormone in the pineal gland is directly linked to exposure to light. Production of melatonin decreases due to exposure to blue light from artificial light, light from monitors, or sunlight. When light decreases in intensity and it gets dark, production of melatonin resumes.
Balanced hormone levels are crucial to performance. An earlier study (Kleitman, 1933) showed that variations in performance throughout the day followed the same cycle as the cortisol curve in normal Circadian rhythm (see figure 2). Cortisol rises rapidly in the morning and peaks around noon. It gradually reduces throughout the rest of the day. Researchers studied cognitive skills such as speed and accuracy of performance of a number of tasks, amongst others. For example, the speed with which one is able to deal and sort cards, and multiply and decipher codes. What did they find? Cognitive performance was almost completely in keeping with physiological factors such as body temperature and heart rate, the same applied when they looked at averages over twenty days.
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SUBJECT H.K.
Average over 20 days 98.1
112
97,9
108
Dealing cards speed
104 100 108
Oral temperature
97,7 97,5 62
104
Sorting cards speed
100 112
60
Heart rate
58 56
108 Mirror drawing speed
104 100
140
Mirror drawing accuracy
120 100
96
180 112
160
108 104
Code transcription 140 speed 120
100
100
118
220 Multiplication speed
112 106
Code transcription accuracy
180
Multiplication accuracy
140 100
100 7
8 10 12 14 16 18 20 22 23 Time of day
7
8 10 12 14 16 18 20 22 23 Time of day
Figure 2 Body temperature and heart rate show increase and decrease curves equivalent to the speed with which one can deal and sort cards, decipher codes and carry out multiplication. The same tendency was observed over a 20day average. These curves thus correlate with cortisol production throughout the day. It can be concluded that biorhythm and performance are closely linked and are relatively stable.
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Cognitive performance
Mood
Pupillary constriction Thalamus
Sleep/Wake state
Locomotor activity
Cortex
Memory Figure 3 Light enters via the retina and sends signals to the pineal gland. Different wavelengths produce differences in hormone production. These differences in hormone production have an effect on, amongst others, cognitive performance, mood, memory and Circadian rhythm.
Pineal Gland (Pijnappelklier)
Hypothalamus
Circadian rhythms
Office workers are just like astronauts Office workers function almost just as unnaturally as astronauts do. After all, office workers’ bodies are confused by all kinds of artificial signals for many hours of the day. The light absorbed via the eyes rarely comes from the sun anymore. Bulbs, computer monitors and TV screens are the primary source. When we absorb excessive light from computer screens, it is harder to fall asleep. The cause? These screens primarily radiate wavelengths that belong to the blue spectrum and long-term exposure disrupts hormone balance; that leads to an excess of cortisol in the blood and inhibits the production of melatonin. Although employers are increasingly investing in interventions to optimise performance on the shop floor, good lighting remains uncharted territory for many organisations. Fluorescent tube lighting with static blue-white light is generally the rule rather than the exception on the shop floor.
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Dynamic light enhances performance Astronauts experience a deterioration in cognitive performance and mood due to changes in light exposure. The same applies to office workers; they can suffer from the same symptoms in the long term. Many hours of exposure to blue light and a lack of natural daylight can upset biorhythm, which can result in disturbances in cognitive performance and mood in the long term. Exposure to dynamic light during office hours is essential for sustainable employability. What can we do to counteract the negative effects of artificial light, light from computer monitors, and the lack of natural daylight on biorhythm? Outdoor breaks have a positive effect on biorhythm and should be promoted more on the shop floor. No artificial light is as powerful as natural light; the intensity of office lighting is between 300-500 lux on average, while natural daylight on a clear day can reach an intensity of 125,000. Increasing your daily exposure to natural light gives your biorhythm an indication of the time of day, which promotes balanced hormone levels. There are also various kinds of software tools, such as Work & Move, which encourage employees to take breaks from work and actively engage in breaks for exercise and recovery. These are useful tools that provide the necessary mental and physical relaxation.
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No time for a break? Naturally, light also reaches the retina via windows. It is therefore advisable to place workstations close to windows and to always favour such workstations over those that only have artificial lighting. In addition, there are now all kinds of solutions for preventing disruptions to biorhythm caused by light from monitors. For example, the F.lux application has been in existence for some time. The F.lux application can be downloaded for free. The app asks you to enter your location and then adjusts the light from your computer screen to the time of day at your latitude and longitude. The natural variation of blue light to red light is adjusted gradually on the monitor.
In summary Exposure to dynamic light during office hours is essential for sustainable employability. To enable office workers to perform better, it is important creating more natural daylight in the workplace. Would you like to know more about this subject or about BakkerElkhuizen? Then contact us. Myrthe van Stralen Senior Consultant | Research and Development BakkerElkhuizen (part of Office Athletes)
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Sources •
Derk-Jan Dijk, David F. Neri, James K. Wyatt, Joseph M. Ronda, Eymard Riel, Angela Ritz-De Cecco, Rod J. Hughes, Ann R. Elliott, G. Kim Prisk, John B. West, Charles A. Czeisler(2001). Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. American Journal of Physiology - Regulatory, Integrative and Comparative Physiology. Published 1 November 2001 Vol. 281 no. 5, R1647-R1664 DOI
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Flynn-Evans, E., Barger, L.k., Kubey, A.A., Sullivan, J. P., Czeisler, C.A. et al. (2016) Circadian misalignment affects sleep and medication use before and during spaceflight. Published Online www.NASA.gov.
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Kleitman N. (1933) Studies on the physiology of sleep: VIII Diurnal variation in performance. Am J Physiol 1933; 104: 449-56.
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Lockley, Steven W., George C. Brainard, and Charles A. Czeisler. “High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light.” J Clin Endocrinol Metab 88.9 (2003): 4502- 4505.
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Lockley, Steven W., et al. “Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans.” SLEEP 29.2 (2006): 161
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