Biological Darkness: The Forgotten Nutrient of Human Health and the Built Environment

Written By UTA Architects Ltd

Why the absence of light is as biologically essential as daylight and how modern buildings deprive us of both

Light has dominated architectural thinking for over a century. Daylight factors, lux levels, glare indices and luminous efficacy are embedded in standards, planning policy and design culture. Darkness, by contrast, has too often been treated as a void to be eliminated, a problem to be solved with brighter lamps and longer operating hours.

Yet biology tells a more complex story. Human physiology evolved under predictable cycles of bright days (in outdoor daylight) and genuinely dark nights. Darkness is not simply the absence of light but an active biological signal that regulates hormones, metabolism, immune repair, emotions and cognition. When darkness is eroded, health consequences follow.

The term biological darkness has emerged from chronobiology and neuroscience to describe lighting conditions that are insufficient to support normal ‘circadian signalling’ or ‘biological clock’ (and therefore optimum sleep-wake cycles and daytime energy levels). Crucially, biological darkness should (but cannot) occur at night when spaces are too bright. Whereas biological darkness should not (but does) happen during the day when indoor environments are too dim. Modern buildings now produce both problems simultaneously.

1 — WHAT IS BIOLOGICAL DARKNESS?

Defining a Misunderstood Concept

Biological darkness refers to environmental light conditions that fail to provide adequate circadian ‘daytime light’ cues for the human inner ‘biological clock’ (1). It is not synonymous with visual darkness and does not necessarily mean pitch blackness.

Biological darkness is a concept used to describe light levels low enough to permit melatonin (sleep hormone) secretion and night-time physiological processes. However, the term has expanded to include a paradox of modern life: people spending daytime hours in light levels so low that, biologically, the body interprets them as night-like.

Research led by Nowozin and colleagues (2) describes this phenomenon as ‘Living in Biological Darkness’ (LBD). Their studies imply that people in modern urban environments often spend most of the day in light environments with below 100 lux illumination (in the winter), far below the 1,000 to 100,000 lux light levels typically experienced outdoors (2).

Biological Darkness Is Not Visual Darkness

A room may appear adequately lit for reading or screen work, yet still be biologically dark. This is because:

  • Circadian photoreception is mediated primarily by ‘intrinsically photosensitive retinal ganglion cells’ (ipRGCs) in the eye

  • These cells are most sensitive to short-wavelength blue light

  • They require higher light intensities than vision to trigger robust circadian responses

As a result, a 300-750 lux office that meets visual standards (3) can still deprive the brain of meaningful daytime light signals (4).

2 — THE BIOLOGY OF DARKNESS AND THE CIRCADIAN SYSTEM

The Suprachiasmatic Nucleus and Timekeeping

At the core of human circadian regulation lies the suprachiasmatic nucleus (SCN) in the hypothalamus (5). This cluster of neurons acts as ‘the master clock’, synchronising ‘peripheral clocks’ in organs such as the liver, gut, pancreas and immune system. (6)

Light and darkness reach the SCN through the eyes. Daytime light strengthens circadian health, whereas night-time darkness permits healthy nocturnal hormonal cascades.

According to Josephine Arendt’s work on melatonin, darkness is not passive but instructive. Melatonin secretion signals night-time, promotes sleep initiation, supports immune regulation and even seems to possibly act as an antioxidant (7).

Melatonin as the Darkness Hormone

Melatonin is a hormone that promotes sleepiness. Its production begins in dim light and is rapidly suppressed by even modest light exposure. Studies show that:

  • Light levels as low as 10 to 30 lux can suppress melatonin at night (8). In some individuals 1 lux has been reported. (The light of a candle is approx. 10 lux.)

  • Blue light is particularly disruptive (9)

  • Chronic suppression is associated with sleep disorders, metabolic dysregulation and mood disturbance

As reported in “Dark matters: effects of light at night on metabolism”, light at night interferes with glucose metabolism, insulin sensitivity and lipid regulation (10).

The International WELL Building Institute (IWBI) states: “Exposure to light at night has also been associated with negative health effects, such as breast cancer, circadian phase disruption and sleep disorders.” (11)

3 — LIVING IN BIOLOGICAL DARKNESS DURING THE DAY

A Hidden Epidemic of Dim Days

One of the most counterintuitive findings in recent lighting research is that biological darkness is now a daytime problem.

According to de Zeeuv et al: “Living in Biological Darkness…” (12), many people in modern societies spend between 60 and 90 percent of their time in light levels below 100 lux.

For context:

  • Typical outdoor daylight on a sunny, cloudless day can be 100,000 lux or more

  • A cloudy winter day can still deliver 1,000 lux or more

  • Many offices provide 300 lux (measured horizontally, not at the eye)

This means that indoor workers may rarely experience biologically meaningful daylight.

Physiological Consequences

The consequences of daytime biological darkness include:

  • Increased subjective sleepiness

  • Reduced alertness and cognitive performance

  • Flattened circadian rhythms

  • Reduced resilience to evening light exposure

From the WELL Building Standard, ‘Light’ Concept: “Light deficiencies affects the functioning of the circadian system and quality of sleep. Disruption of circadian rhythm has been linked with obesity, diabetes, depression and metabolic disorders.” (11)

4 — BIOLOGICAL DARKNESS, MENTAL HEALTH AND EMOTIONS

Depression, Seasonality and Light History

Light history matters. The human nervous system adapts to habitual light environments. Prolonged exposure to dim days increases sensitivity to light at night and reduces circadian robustness.

Studies of Antarctic winter crews demonstrate that months of darkness can alter pupil light sensitivity long after daylight returns (13). This plasticity is adaptive in natural environments but problematic in artificially lit ones.

Recent work by de Zeeuw et al. shows that even low-level pre-midday lighting can increase the risk of depression in healthy subjects (1). This suggests that biological darkness actively impacts emotions.

Habitual low daytime light exposure during winter has been found to be associated with altered sleep architecture (2) and increased vulnerability to depressive symptoms (e.g. ‘seasonal affective disorder, ‘SAD’).

5 — BUILDINGS AS ENGINES OF BIOLOGICAL DARKNESS

Architectural Root Causes

Many contemporary buildings unintentionally manufacture biological darkness through:

  • Deep floor plates with limited daylight penetration

  • Low window-to-wall ratios

  • Fixed solar shading features that cannot be adjusted

  • Electric lighting not optimised to human circadian rhythms

Standards and Their Limitations

The British Standard BS EN 12464‑1:2021 recommends around 300 to 1000 lux for office tasks. It does also recognise, however, that these values should be used as a ‘first step’ and that the biological, human performance, wellbeing, emotional and health considerations of lighting require ‘additional design practices and methods to those currently in use’. (14)

According to circadian lighting design principles, indoor lighting recommendations must differentiate between daytime, evening and night-time exposures to support good health.

Wildlife-friendly lighting and circadian rhythm support would be welcome additions to national technical lighting design requirements and ‘best-practice’ recommendations.

The WELL Building Standard, which is a voluntary ‘healthy building’ certification standard, does promote lighting that strengthens circadian rhythms via higher levels of natural daylight and electric lighting levels supportive of the circadian rhythm.

6 — BIOLOGICAL DARKNESS AT NIGHT AND LIGHT POLLUTION

Artificial Light at Night (ALAN)

While daytime biological darkness weakens circadian signals, night-time light pollution disrupts them even more effectively. As mentioned above, light levels as low as 10-30 lux can suppress melatonin at night (8), depending on a person.

Artificial light at night ‘delays circadian phase’ and therefore makes it more difficult to fall asleep, while also impairing sleep quality. ALAN has also been associated with increased risks of obesity, diabetes, cardiovascular disease and certain cancers in humans (15).

Ecologically, the consequences are profound. ‘Scotobiology’ (the study of the biological need for darkness) has discovered that many species depend on darkness for navigation, reproduction and predator avoidance.

UK planning regulations do take wildlife‑friendly lighting into account, particularly where protected species (notably bats) may be affected. However, this consideration usually arises through biodiversity law, planning policy and guidance, rather than through a single, explicit “wildlife‑friendly lighting” regulation or a technical design requirement. Therefore the actual requirements to implement lighting that is ecologically appropriate depend on the project, species found on the existing site and the local planning authority (LPA) policies.

The Loss of True Night

For most of human history, the night sky was a shared and universal, awe-inspiring experience: a source of navigation, scientific discovery, cultural meaning and wonder. Today, however, that experience is rapidly disappearing. Artificial light at night has transformed nocturnal environments so profoundly that the majority of humanity can no longer see the Milky Way from where they live. The ‘dark sky movement’ emerged in response to this loss, advocating for the protection and restoration of natural darkness as an essential environmental, cultural and public health resource.

‘Citizen science’ data show rapid global reductions in star visibility due to skyglow from artificial lighting, cities and even satellites (16).

7 — DESIGNING FOR DARKNESS AND DAYLIGHT TOGETHER

A Circadian Design Ethic

Healthy buildings require both bright days and dark nights - i.e. a cyclical rhythm between light level extremes. This demands a shift from static lighting targets to temporal and circadian lighting design.

Key principles include:

  • Ensuring sufficient morning and daytime daylight exposure for all spaces where people spend significant time in

  • Reducing blue-rich light in the evening

  • Ensuring genuine darkness in sleeping spaces

  • Considering smart lighting to automate circadian light level changes through the day

  • Incorporating comfortable outdoor spaces into buildings

  • Using EML (equivalent melanopic lux) in lighting design calculations

Equivalent Melanopic Lux (EML) is a lighting metric (referenced in the WELL Building Standard) which makes it possible to quantify how strongly light stimulates the human circadian system. Unlike conventional lux, EML is weighted to melanopsin, the photopigment in eyes that regulates circadian rhythms, alertness and hormone production (17). In simple terms, EML estimates the biological effectiveness of light.

According to Ulrike Brandi’s holistic lighting philosophy, architecture must balance aesthetics, lighting, nature, culture, orientation, sustainability, safety, atmosphere and the human need for darkness (18). She also discusses the concept of ‘lighting masterplans’.

In homes, it is possible to fairly easily change interior lighting and lifestyles to better support good circadian function. Many light fittings now exist that have been designed for circadian support to suit different times of the day. Smart lighting systems provide the added possibility to have lights automatically adjust for morning, day, evening and night-time light levels and colour temperatures, to simulate natural daylight. For best results a lighting designer should be consulted with but much can be achieved through individual research and DIY design also.

Practical Architectural and Management Strategies

For daytime:

  • Shallow floor plates, lightwells, atria, rooflights

  • High-transmittance glazing with adjustable external shading

  • Daylight-responsive automatic lighting controls (photosensors)

  • Workstation layouts near windows (with adjustable shading)

  • Comfortable outdoor environments to encourage time spent outdoors

  • Flexible work times, allowing time outdoors during daylight hours, to suit individual circumstances

  • Encouragement to have meetings, social events and presentations outdoors

  • Electronic ink screens with anti-glare finishes, to enable viewing of screens in daylight

  • Daylight-simulating artificial lights to supplement morning and daylight during dark seasons (e.g. winter in the UK)

  • Professional lighting design with a focus on circadian lighting principles.

  • Occupant survey to assess any lighting preferences and special needs of occupants.

For night-time:

  • Low-level, warm-spectrum lighting below 2700K (e.g. electric candles, red reading lights)

  • Elimination of unnecessary standby lighting

  • Blackout strategies for bedrooms

  • Outdoor lighting designed to avoid light pollution, save energy and be wildlife-friendly

  • Avoidance of late-night computer work and digital screen viewing. (Electronic ink screens can be viewed in red evening light, however, even with backlight turned off.)

  • Blue-light filters for screens and glasses (last resort, not as effective as light reduction)


8 — MULTI-DISCIPLINARY APPROACH

Who Should Be Involved?

Optimising biological darkness and circadian lighting for human health requires collaboration between:

  • Lighting engineers

  • Architects

  • Healthy building specialists

  • Building services engineers

  • Sustainability engineers and specialists

  • Occupational health professionals

  • Healthcare professionals

  • Sleep and circadian specialists

  • Environmental health scientists

  • Urban planners and policymakers

  • Building owners

  • Organisation leaders and decision-makers

  • Facilities managers

  • Ecologists

  • Biodiversity specialists

  • Interior Designers

  • Landscape designers

This is a systems problem, not just a product specification issue.

RESOURCES AND FURTHER READING

DarkSky International

NBS: “Sustainability: An NBS guide to combating light pollution“

Ulrike Brandi: “Light Nature Architecture: A Guide to Holistic Lighting Design”, Birkhäuser, 2023

BRE:

The International WELL Building Institute:

Chartered Institute of Building Service Engineers (CIBSE): ‘LG07 Lighting for Offices’

British Standards:

Dani Robertson: “All Through the Night: One woman’s fight to protect our planet's nature and environment from the effects of light pollution” (book)

Forbes: Jamie Carter:

RICS: Rights of Light

CONCLUSION

Biological darkness reveals an uncomfortable truth about modern progress. In our quest to banish night and illuminate every corner, we have disrupted a regulatory signal older than humanity itself, which regulates almost every cell in our body. Darkness is not a failure of design but a biological requirement.

Healthy, sustainable buildings must learn to choreograph light and dark with the same care given to structure and energy. This means designing days that are bright enough to anchor the circadian system and nights that are dark enough to let the body repair and reset.

The future of healthy architecture lies not in more light, but in wiser light. And sometimes, in the courage to switch it off.

DISCLAIMER

We will not accept any liability for the use or misuse of this information. We can provide formal architectural advice only when appointed on a project.

UTA Architects Ltd https://www.ut-a.com
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