Biomedical research support

Light shift for work shifts

How can biomedical research support retail lighting design?

And yet lighting systems were not applied at night in the history of mankind in the incandescent lamp era. "Arkwright’s Cotton Mills by Night" by Joseph Wright of Derby is one of the first paintings demonstrating light taking over the dark. From 1772 until the mill was closed and used for other purposes, the factory in Cromford, England, was in operation 24 hours a day in 12-hour shifts. At night, it was lit by candles. For some time (before Thomas Edison and James Bowman Lindsay developed their inventions) our nights were required to forfeit darkness for the needs of modern world. Nowadays, the consequences of excessive light at nighttime is regarded as environmental pollution. The night sky as seen by the majority of urban dwellers has an orangeish glow, which is substantially different from the starry dome that our ancestors were used to seeing after sunset. Light pollution is an unnatural scenario, also from the perspective of ecology and health, and medical scientists today can prove that light at night has several behavioural and metabolic effects on animal species, including human beings.

The dialogue between architecture, design and biomedical research is especially important because nowadays we recognize light not only as electromagnetic radiation capable of causing the sensation of brightness or visual stimulus. Light is also the main cue that synchronizes our biological rhythms. For that reason, light is described today as the main biological zeitgeber ("time giver"), and the concept of circadian light is already well established. Through a complex neural network that starts in our retina (which is independent from visual pathways), light stimuli are transmitted in the trigeminal nerve to important cerebral structures, such as the suprachiasmatic nuclei and the pineal gland. The latter is responsible for the production and release of an important hormone: melatonin. These elements function as our main endogenous oscillators, also known as biological clocks, marking our circadian rhythms.

Even though these biological structures are localised in our brain, they have the capacity of transmitting information (nervous electrical outputs and hormonal signals) to several organs and systems in the body, which then respond or react accordingly. The circadian clock works to keep our bodies aligned to the external world. Still, there are a number of circumstances that can interrupt this natural course, leaving us out of sync with the environment. This is referred to as "circadian disruption". Just as the heart needs to beat at a certain rate to maintain its functions, so the luminous inputs translated into cellular activation processes within brain structures need a circadian rhythm as a basis. Through wrongly applied artificial lighting systems, or by subjecting ourselves to artificial light at the wrong times of day/night, we risk losing this rhythm. Reduced time spent under natural light and higher electrical light stimuli during nighttime have been proven to be associated with several adverse outcomes, including sleep disorders, anxiety, depression and a high risk of addiction. Circadian disruption has also been associated with metabolic disturbances, cardiovascular diseases, diabetes, hypertension and breast cancer.

Software exists that aims to quantify how much light can be related to a certain circadian stimulus, the intention being to provide professional lighting designers with more information about how to design considering circadian light. Furthermore, the introduction of lightemitting diode technology is a big challenge for lighting designers. Even though human vision appears to be relatively well adapted to the white light emitted by LEDs, these light sources also show strong peaks in the blue wavelengths ranging from 460 nm to 500 nm. This blueish light is known to give rise to melatonin suppression and support the disruption of human sleep cycles. It has

lso been linked to photochemical retinal injury in animals. Such adverse effects, and even injury, are related to both time of exposure and wavelength, but not total light irradiance. We have to be careful when applying this technology in the architectural spaces we use.

So what does this have to do with retail lighting?
When we think about retail lighting, the first image that comes to our minds is a creative lighting solution that highlights the merchandise, creating a unique consumer experience. Overall, the main goal of the lighting system is to increase brand awareness and enhance sales. However, such architectural spaces are more than simply a place to deposit products to be sold. They also serve as a workspace: in Brazil in 2017 there will be around one million people working in shopping malls alone. That means that health and well-being issues concerning these employees must also be considered when developing lighting strategies for retail spaces.

There is therefore an urgent need to discuss the architectural design of many shopping mall buildings all over the world. Most of them do not allow people to have any visual contact to the outside world. This is a sales strategy aimed towards to keeping consumers totally focused on the interior environment. Any perception of time passing and information about the external environment are impaired. Many scientific studies have demonstrated that when people do not have a view outside during daytime, there is a higher risk of them being more stressed at the end of their working day.

Working shifts is another factor that can cause problems directly related to circadian biology. This relates to the fact that the natural cycle of light and dark is key to keeping our biological clock synchronised. When an employee arrives at a windowless retail space in the morning and leaves at the end

of the day (around 6 pm), his/her body will not receive a sufficient dose of light to guarantee the necessary circadian stimulus. In general, electric lighting systems do not produce a sufficiently high illuminance, or quality of light, to ensure the circadian system remains synchronised. On the other hand, employees who take the afternoon turn, starting at around 4 pm and working until 10 or 11 pm, may experience longer exposure to natural light and, in contrast, a shorter period of darkness. What are the consequences of such light and dark patterns for employees in retail spaces?

There is growing body of research into what has been termed social jet lag, which is described as a biological misalignment that results from alternated work/activity and free days. This phenomenon relates to the incompatibility between the social and the biological clock. Social jetlag has been associated with a number of neuropsychiatric disorders, such as aggression and behavioural problems, mood disorders, cognitive impairment (e.g. work and academic performance), and substance use. In addition, it has been associated with cardio- metabolic risks.

Finally, it is important to consider different human chronotypes – that is to say how individual physiological adaptations to the 24-hour light/ dark cycle reflect on different responses to health and disease states. Chronotypes relate to individual preferences when allocating day-to- day tasks, including sleep and wake times. They influence not only physiology and metabolism, but also aspects such as cognitive performance, and psychiatric symptoms and disorders.

Individuals who work in retail spaces frequently need to get up early in the morning to start their daily routines, and are less exposed to outdoor light (and darkness) during working hours. Exposure to unnatural patterns of light-dark cycles and the inadequacy of certain chronotypes to align to activities assigned within a given period are key factors in the disruption of normal physiology and the emergence of social jetlag.

Research 1: Light patterns in retail spaces and the consequences for employees’ health and well-being
For two years (2008 to 2009), we developed an exploratory study that focused on retail lighting systems and their impact on employees. We assessed visual, biological and emotional aspects of lighting considering the individuals who worked in the lit environment. In this study, our group recorded a high degree of dissatisfaction with the lighting system in the three groups of subjects, all females aged from 18 to 65 years old. One group working in street retail stores with visual contact to the exterior, and two other groups in shopping malls without visual contact to the exterior and with different working schedules. Moreover, satisfaction with the lighting design was associated to emotional and biological factors. To sum up, the results demonstrated that:
1. The more dissatisfied the employees were with the assessed aspects, the more depressed they were.
2. Displeasure was expressed through complaints of having to work in environments without windows, and therefore being exposed to electric lighting most of the day or into the night, depending on their shift. The main problems identified were: difficulty regarding time orientation, lack of visual contact with the outdoors, excess or lack of lighting to carry out their tasks, and problems related to non-visual issues, such as excess heat or noise produced by the artificial light sources.
3. Shopping mall workers claimed that having no visual contact with the outside world led to the worst possible levels of assessed anxiety and stress.
4. Evidence of an inverse correlation was found between the average general illuminance of a store and satisfaction with the lighting. In addition, there was a positive correlation of this variable with scores in a screening questionnaire for mental disorder and depression when shopping mall employees’ working hours were from 10 am to 4 pm. Changes in cortisol levels in this group may be related to high stress and the lack of contact with natural light.
5. Since circadian rhythm regulation depends on the time and duration of exposure to light, employees working from 2 pm to 10 pm in windowless spaces seemed to be more influenced by light in the workplace, perhaps because they were subjected to light for a prolonged period. In this group we recorded the highest average general illuminances (up to 700 lux). This was accompanied by physiological alterations in melatonin production and highly negative feedback in the assessment of depression.

This research suggests that the lighting systems installed in the retail spaces did not consider the human factors.

Research 2: Hospital lighting and the difference between working in spaces with and without windows

After focusing on the lighting systems in stores, we wanted to discover if the type of work activity could be a variable to confound the relation of lighting systems and employees’ circadian rhythms. Therefore, we performed another crosssectional study using the same methodology but in a building with a different use: the hospital. Individuals were allocated into two groups according to their workplace. We recruited some employees working in rooms with windows and others without windows. As in the first study, all participants were women.

Our results showed a high degree of dissatisfaction with the lighting system in the group without any visual contact to the outside world. Moreover, the level of satisfaction with the lighting design was shown to be associated with emotional and biological factors. In addition, subjects who worked in windowless spaces showed higher levels of melatonin at 8 pm and lower levels of melatonin at 10 pm. Night-time melatonin was found to be negatively correlated to depressive symptoms and scores for sleep quality. This indicates that people would more likely suffer from depressive symptoms and report poor sleep quality, the lower their night-time melatonin levels.

Individuals working most of the time only under electric lighting also show higher cortisol levels at 10 pm.

This night-time cortisol positively correlates with scores gained from questionnaires for psychiatric screening and depressive symptoms, suggesting higher chances of psychiatric illnesses in this group of people. These results may reflect signs of chronodisruption, because metabolism disorders associated with cortisol and melatonin are also related to several diseases.

This second study confirmed many findings from the first one. It is not only the functional aspects of light that must be considered when developing a lighting (or architectural) concept, but also the human needs. The regulation of circadian and related cycles must be considered as a lighting requirement in any workspace.

Human Centric Lighting: a new buzzword for the retail market Due to the research on the biological influence of lighting in the last couple of decades Human Centric

Lighting (HCL) has become an established concept – or term – in the lighting industry. Considering not just the visual aspects, but also the non-visual effects of light, it is focused on how to help people feel better and live healthier in architectural spaces. This naturally also applies to retail lighting. Nevertheless, we need to do more research on how to deal with different chronotypes (night owls or morning larks) in the same space. For example, the quality of the light the different chronotypes are exposed to (luminous intensity and colour temperature) needs to be different. Furthermore, the optimisation of lighting regimes, including the further development of LED as light sources suitable for work spaces, is necessary. Not only to save energy but also to improve performance. Although it is difficult to quantify the direct benefits of the so-called HCL approach in retail spaces, there are two reports that claim significant growth in the wholesale and retail market.

Biomedical research is actually what human-centric lighting is truly about. It reveals that people are more likely to complain about insufficient sleep and depressive symptoms if they are exposed to less sunlight during daytime and if they work in windowless spaces. Individuals who work in spaces with windows have more exposure to light during working hours and about 45 minutes more sleep per night compared to those working in windowless spaces. Moreover, some studies suggest that an exposure to sunlight of at least three hours per day can lead to lower levels of stress and higher satisfaction at the workplace.

From our experience, we recommend as best practice in the human-centric sense in retail spaces:
-->Allow as much visual contact to the outside world as possible
--> Create the possibility for employees to control the lighting conditions over the course of the day
--> Be careful when using light sources that suppress melatonin production at night-time and remain cautious when using new technologies until their influence on health is confirmed
--> Avoid use light sources with pre- dominantly blue waves on the spectrum after dark, thus reducing the risk of causing harm to the circadian system 
--> Adopt lighting techniques that incorporate highlighting merchandise – which is the key to attracting customers to buy – and using lower light levels for the general lighting for employees

-->  Explore the potential of reflected or indirect light sources that could best suit employees ́ health and well-being at night-time.


There is a need to engage chrono- biologists, architects, designers and the lighting industry in discussion in order to think about strategies for health promotion. Both studies mentioned in this article highlight how important the lighting systems are for human health and well-being in retail stores and hospitals.

The steadily growing amount of evidence contained in scientific literature reinforces this assertion. By speaking openly about the correlation between light and health, company owners can be encouraged to invest in employees’ satisfaction and feeling of well- being and, indirectly, in their productivity on the job.


1 – For more information on social jetlag, see: Beauvalet, J.C., Oliveira, M.A.B., Quiles, C.L., Ilgenfritz, C.A., Hidalgo, M.P., Tonon, A.C. (2017). Social jetlag in health and behavioral research: a systematic review. Chronophysiology and Therapy. [Article in press]

2 – Martau, B. T. (2009). The light beyond vision: lighting and its relation- ship with health and wellbeing of employees at street and shopping mall retail stores in Porto Alegre. Doctoral’s Thesis. University of Campinas, Brazil.

3 – This study had a collaboration with Maria Paz Hidalgo, Paulo Sérgio Scarazzato e Clarice Luz.
4 – Harb, F., Hidalgo, M. P., Martau, B. (2014). Lack of exposure to natural light in the workspace is associated with physiological, sleep and depressive symptoms. Chronobiology International. 32(3):1-8
5 – For more information on chronotypes, see: Adan, A., Archer, S.N., Hidalgo, M.P., Di Milia, L., Natale, V., Randler, C. (2012). Circadian typology: a comprehensive review. Chronobiology International, 29(9):1153-75. 6 – For further information, see: "Human Centric Lighting: Going beyond energy efficiency", a Report from 2013; and "Quantified benefits of Human Centric Lighting; Final Results" from April 2015 by ZVEI, Lighting Europe and A.T. Kearney.