UNDERSTANDING NON VISUAL NEEDS
Good daylighting influences our health and wellbeing, ensuring we are alert and productive when we need to be, and able to sleep and recover when we need to.1 While it may not be possible or desirable to design out artificial light from our buildings entirely, we can be more aware of the benefits of maximising daylight.
UNDERSTANDING NON VISUAL NEEDS
KEY LEARNINGS
- Understand how the non-visual aspect of light differs from the visual aspect.
- Be aware of how daylight dictates circadian rhythms.
- Give examples of how exposure to daylight has a positive influence in different environments.
As good as some artificial lighting is, no electric light source has yet been created that can match the quality of natural light. Artificial lighting cannot mimic the variation in daylight’s spectrum throughout the course of a day, a season, or a year. As part of human chronobiology, we have evolved circadian rhythms – and daylighting as part of building design should reflect the importance of those rhythms.2
NATURAL
Daylight
ARTIFICIAL
LED
Fluorescent
Halogen
ARTIFICIAL
LED
Fluorescent
Halogen
Daylighting is more than the visual aspect of light It’s easy to think of light as being required only for vision. After all, light levels are typically specified in terms of visual needs like the level of illumination needed at a surface to allow safe working. In that context, we are thinking about the ‘image forming pathways’ - the image processing in the eyes and the brain that creates what we see2.
However, the non-visual aspect of light, or the non-image forming pathway, is every bit as critical to how the body functions.
Disruption to circadian rhythms can cause ‘social jet lag’, while more severe seasonal affective disorders can occur due to the limited availability of daylight in winter. In short, our health (the circadian system) and wellbeing (the perceptual system) are both highly dependent on daylight3.
How daylight stimulates major control centres of the body How our biology responds to light intensity, duration, timing, and spectrum is highly complex and varies greatly between our visual and circadian systems. In the human body, the nervous system and the endocrine system are significant health keepers4.
When we speak about health, balance and physiological regulation, we are referring to the functions of these two systems. They are directly stimulated and regulated by light, through photosensitive ganglion cells in the retina of the eye. We therefore need daily daylight exposure, because daylight is rich in the spectrum to which the non-visual system is most sensitive5.
Catching the blue wave Most of us have become aware of the power of blue light, especially when emitted by electronic devices that we use just before sleeping. Different wavelengths of light have different energy, which the human eye interprets as different colours. In the visible light spectrum, blue light has a particularly strong impact on alertness and hormone production (think of the way daylight changes colour from sunrise to sunset – across time, the hours of bluest light have corresponded with when humans have been most active). We therefore naturally need less blue light later in the day, in order to promote sleep – which is why blue light-emitting devices are bad for us at bedtime6.
Circadian rhythms – the daily cycle that influences health and wellbeing Circadian rhythms are the daily rhythms that dominate many aspects of human physiology and behaviour. The dynamic variation of light, both daily and seasonally, is a critical factor in setting and maintaining our circadian rhythms. They control sleep/wake cycles, alertness and performance patterns, core body temperature rhythms, and the production of the hormones melatonin and cortisol7.
We know that outdoor daily light exposure allows us to regulate our sleep/wake timing and levels of alertness. But the reality is that we spend 90% of our time indoors, where we are exposed to relatively low light levels of a limited spectral range, and where the patterns of light and darkness occur at irregular intervals. Inadequate light exposure can disrupt normal circadian rhythms8.
An appropriate light signal during the day, and darkness at night, are critical in maintaining our overall health. Sleep disruption alone has been linked to poor cognitive function, stress, depression, poor social interaction, metabolic and cardiovascular disease, increased susceptibility to infection, and even cancer9.
Exposure to daylight throughout the day
Morning light is the most important signal to align our body clock. It increases our levels of alertness, allowing increased performance at the beginning of the day.
From mid-morning to early evening, high levels of daylight, allow the body to regulate its sleep/wake timing and levels of alertness.
Reduced light levels in the evening, and a dark room with blackout, promotes sleep at night.
There are other external time markers, but daylight’s characteristic light/dark variation, continuity and spectral composition are excellent synchronisers of our circadian rhythm. The inability to provide building occupants with a good overall lighting environment can have subsequent impact on health and place a substantial burden on the individual, society, and the broader economy.
How much light do we need to synchronise our body clocks? Research on the nonvisual effects of light on humans is still in its relatively early days – it was only in 1998 that Russell Foster and his team of researchers discovered that the human eye contains a third light sensor! They uncovered that whilst the rods and cones of the retina provide us with our sense of space or vision, a small number of photosensitive retinal ganglion cells detect the overall amount of light in the environment and then align the body clock – providing us with our sense of time10.
This discovery indicated that people without the ability to see, are still able to regulate their internal clock.
It is yet to be concretely determined just how much, and what kind of light exposure we need to trigger healthy circadian responses, but current research does suggest that ‘doses’ of light above 1000 lux trigger melatonin suppression and further research to support 2500 lux full spectrum light for therapy. There is also evidence that high lighting levels do not need to be constant throughout the day – 30 minutes outdoors during daylight hours has a light entrainment effect that can last several hours11.
Given that we spend up to 90% of our time indoors and that for many people it can be difficult to even get 30 minutes outdoors during good daylight hours, the evidence we have so far can help us to design for healthy daylight in buildings. Whilst it may not be appropriate to aim for levels above 1000 lux in all areas of a building (for glare and thermal considerations), ensuring there are specific areas bathed in higher levels of daylight can have a significant impact on a user’s circadian rhythm and their subsequent health and productivity. Spaces such as lunch areas, social meeting spaces and breakout flexible working areas in office buildings and schools, where occupants spend time in shorter intervals (and perform tasks that also benefit from particularly high light levels), would be perfect for consideration of extra daylight attention.
Using daylight to enhance performance and productivity Many studies show that the performance and productivity of workers in office, industrial, and retail environments can increase with improved quality of light. Companies have recorded an increase in productivity of their employees of about 15% after moving to a new building with better daylight conditions12.
Another study, meanwhile, demonstrated that greater satisfaction with lighting conditions contributed to environmental satisfaction, which, in turn, led to greater job satisfaction13.
Studies also show that daylit environments lead to more effective learning. It was found that students in classrooms with the most window area or daylighting produced 7% to 18% higher scores on standardised tests than those with the least window area or daylight14.
Using daylight to combat depression-related illnesses Seasonal affective disorder (SAD) is a depression-related illness linked to the availability and change of outdoor light in the winter. Reports suggest that 0.4% to 9.7% of the world's population may suffer from SAD. Up to three times that number – primarily in Northern America and Northern Europe – have signs of the affliction (called sub-syndromal SAD, or S-SAD) without it being classified as a major depression.
Light therapy with exposure levels at the eye of between 2500 lux (for 2 hours) or 10,000 lux (for 30 minutes) has shown to be an effective cure against SAD. Exposure to daylight outdoors (~ 1000 lux) can also reduce SAD symptoms15.
Light therapy can also be used to treat other depression-related symptoms (e.g., non-seasonal depression, premenstrual, bulimia).
Impact of daylight in hospital rooms There is evidence that daylight exposure can affect postoperative outcomes in patients and, consequently, that daylight should be a consideration in hospital design.
Ulrich (1984) reported that hospital patients with a view of green spaces, as opposed to those with a view of a blank brick wall, recovered more quickly from surgery and required less post-operative pain medication16. Beauchemin and Hays (1998) found that patients on the sunnier side of a cardiac intensive care ward showed lower mortality rates than those on the less-sunny side17.
Seeing the complete picture on good daylighting Good daylighting design finds a balance of the visual and non-visual aspects of daylight, improving quality of life for occupants in a holistic way. Since the optimal balance is unique for every building, it’s important to understand from the outset what outcomes are most desirable. Occupancy times, and needs and behaviours in a space, will all affect this. Without a goal in mind, a building might fail to deliver the good daylighting that is so important.
» Read on: Using EN17037 to achieve to good daylighting
1 Boyce, P., Hunter, C. and Howlett, O. (2003) The Benefits of Daylight through Windows, Lighting Research Center, Rensselaer Polytechnic Institute. · 2 Houser, K. (2019) The Rise of Human Centric Lighting. Daylight Symposium 2019, Paris. https://www.youtube.com/watch?v=OWZJ-Xjpg6g · 3 Roenneberg, T. (2019) Buildings of the future need light and chronobiology. Daylight Symposium 2019, Paris. https://www.youtube.com/watch?time_continue=12&v=eifINWO1ZRk&feature=emb_title · 4 Edwards, L., Torcellini, P. (2002) A Literature Review of the Effects of Natural Light on Building Occupants, National Renewable Energy Laboratory, U.S. Department of Energy. · 5 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, Daylighting Quality. https://www.velux.com/what-we-do/research-and-knowledge/deic-basic-book/daylight/daylighting-quality · 6 Christoffersen, Jens. (2011). The importance of light to health and well-being. · 7 Pechacek, C. S., Andersen, M., Lockley, S. W. (2008) Preliminary method for prospective analysis of the circadian efficacy of (day)light with applications to healthcare architecture. Leukos, 5(1), 1-26). · 8 VELUX (2014). Daylight Energy and Indoor Climate Basic Book, Daylighting Quality. https://www.velux.com/what-we-do/research-and-knowledge/deic-basic-book/daylight/daylighting-quality · 9 Circadian House report (2013) Circadian House - Principles and Guidelines for Healthy Homes. VELUX report http://thedaylightsite.com/library-3/research-publications/papers/ (accessed: 2022-09-19). · 10 Daylight and Architecture (2022). The Vital Daylight: Russell Foster. https://www.daylightandarchitecture.com/the-vital-daylight/ · 11 Reinhart, C. (2014) Daylighting Handbook I. p. 85 · 12 Edwards, L., Torcellini, P. (2002) A Literature Review of the Effects of Natural Light on Building Occupants, National Renewable Energy Laboratory,U.S. Department of Energy. · 13 Veitch, J. A., Charles, K. E., Newsham, G. R., Marquardt, C. J. G. and Geerts, J. (2003) Environmental Satisfaction in Open-Plan Environments: 5. Workstation and Physical Condition Effects. IRC Research Report RR-154. Institute for Research in Construction.National Research Council Canada, Ottawa, ONT, K1A 0R6, Canada · 14 Heschong, L. (2002) Daylighting and Human Performance, ASHRAE Journal,vol. 44, no. 6, pp. 65-67. · 15 Wirz-Justice, A., Fournier, C. (2010) Light , Health and Wellbeing : Implications from chronobiology for architectural design, World Health Design, vol. 3. Sloane, P. D., Figueiro, M., & Cohen, L. (2008). Light as Therapy for Sleep Disorders and Depression in Older Adults. Clinical geriatrics, 16(3), 25–31. Reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3839957/ · 16 Ulrich, R. S. (1984) View through a window may influence recovery from surgery. Science, 224(4647), 420-421. · 17 Walch, J. M., Rabin, B. S., Day, R., Williams, J. N., Choi, K., Kang, J. D. (2005) The effect of sunlight on postoperative analgesic medication use: A prospective study of patients undergoing spinal surgery. Psychosomatic Medicine, 67(1):156-163