Light as a biological factor in healthcare facilities: How lighting supports circadian rhythms, recovery, and healing
From light to biology: A paradigm shift in lighting design
Circadian rhythm: The biological foundation of human functioning
Why do hospitals disrupt biological rhythms?
What does the research say?
Light as a component of Evidence-Based Design
Key takeaways
FAQ – Biological lighting and healthcare facilities

Light as a biological factor in healthcare facilities: How lighting supports circadian rhythms, recovery, and healing

Name: Lenalighting
Address: ul. Kórnicka 52, Środa Wielkopolska, Wielkopolskie, 63-000, Polska
Telephone: 61 28 60 300

29.07.2026

Just a few decades ago, lighting design in healthcare facilities focused almost exclusively on providing adequate visual conditions. The primary objective was to achieve the required levels of illuminance, uniformity, glare control, and color rendering in accordance with applicable standards. While this approach remains the foundation of safe lighting design, modern knowledge in chronobiology, neurobiology, and environmental medicine has demonstrated that it is no longer sufficient.

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Light is not merely a factor that enables visual perception. It is also one of the most important regulators of human physiological functioning. It affects circadian rhythms, hormone secretion, sleep quality, cognitive performance, metabolism, and regenerative processes. Consequently, lighting has become a key component of the healing environment, capable of supporting the treatment process or, if poorly designed, contributing to reduced patient well-being and increased strain on healthcare staff.

This is why modern healthcare design increasingly recognizes light as an active therapeutic tool. In this context, lighting design extends far beyond compliance with illuminance requirements. It becomes part of a broader design strategy aimed at creating environments that promote healing, enhance patient comfort, and improve staff performance and safety.

From light to biology: A paradigm shift in lighting design

For decades, lighting design was based on the assumption that the human visual system was the sole recipient of light. As a result, lighting quality was assessed through parameters such as illuminance (lx), color rendering index (CRI), unified glare rating (UGR), and uniformity.

The breakthrough came in the early 21st century with the discovery of a third class of retinal photoreceptors: intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells contain melanopsin and are not responsible for vision itself but rather for transmitting light information to the suprachiasmatic nucleus (SCN), the body's central biological clock.

This discovery fundamentally changed our understanding of the role of light. It became clear that the human body responds not only to the amount of light required for vision, but also to its spectral composition, timing, direction of incidence, and variability throughout the day.

In response to these scientific findings, the International Commission on Illumination (CIE) published the standard CIE S 026/E:2018, introducing a framework for evaluating the biological impact of light using melanopic quantities. Today, this document serves as one of the most important references for lighting design that considers circadian effectiveness.

This represents a fundamental shift in design philosophy. Traditional lighting standards answer the question:

“Can the user see properly?”

Modern lighting design must also ask:

“Does the lighting environment support healthy physiological functioning?”

Circadian rhythm: The biological foundation of human functioning

The circadian rhythm is an internal mechanism that synchronizes the body with the 24-hour cycle of day and night. It governs virtually all physiological processes, including hormonal regulation, body temperature, metabolism, immune system activity, sleep, and wakefulness.

The most important synchronizer of this rhythm is light.

Exposure to appropriately designed light in the morning suppresses melatonin production and increases cortisol levels, enhancing alertness, concentration, and readiness for activity. In the evening, the opposite should occur. Reduced light exposure, especially reduced blue-light content, allows melatonin secretion to begin and prepares the body for sleep.

Under natural conditions, this process occurs automatically. Problems arise when individuals are isolated from natural daylight patterns for extended periods.

Hospitals are a prime example of such environments.

Why do hospitals disrupt biological rhythms?

Healthcare facilities operate continuously, 24 hours a day. Many spaces have little or no access to daylight. At the same time, both patients and staff often remain in these environments for many hours, days, or even weeks.

This is particularly true in:

Intensive care units (ICUs)
Post-operative recovery wards
Geriatric units
Psychiatric wards
Diagnostic imaging departments
Operating theatres
Laboratories
Emergency departments

In such environments, users are frequently exposed to nearly constant lighting levels throughout the day. As a result, the body loses one of its primary signals for distinguishing day from night.

Studies conducted in intensive care settings indicate that circadian rhythm disruption is among the most common challenges faced by hospitalized patients. Consequences include:

Poor sleep quality
Prolonged recovery times
Increased incidence of ICU delirium
Greater confusion among elderly patients
Impaired cognitive function
Reduced immune response

A similar phenomenon affects healthcare professionals working shifts. Long-term circadian disruption increases the risk of chronic fatigue, metabolic disorders, and reduced concentration, potentially affecting the safety and accuracy of medical procedures.

What does the research say?

The importance of light for human health and performance has been well documented in scientific literature.

As early as the 1980s, Professor George C. Brainard demonstrated that exposure to light with specific spectral characteristics can effectively suppress melatonin production and influence circadian synchronization.

Subsequent research by Professor Steven Lockley showed that appropriately designed lighting environments can improve alertness, mitigate the effects of shift work, and support healthcare staff working during nighttime hours.

Today, one of the leading authorities in the field of biological lighting is Professor Mariana Figueiro of the Icahn School of Medicine at Mount Sinai. Her research in hospitals and long-term care facilities has demonstrated that appropriate daytime light exposure can improve sleep quality, reduce symptoms of depression, decrease disorientation in individuals with neurodegenerative conditions, and increase daytime activity levels.

These findings have become one of the cornerstones of Human Centric Lighting (HCL) and evidence-based healthcare design.

Light as a component of Evidence-Based Design

Evidence-Based Design (EBD) is a design approach stating that spatial planning decisions should be guided by reliable scientific evidence rather than solely by designer experience or architectural trends.

In healthcare environments, EBD is particularly important because environmental quality directly affects treatment outcomes. The approach encompasses factors such as acoustics, daylight access, contact with nature, indoor air quality, ergonomics, and lighting design.

Within this framework, light ceases to be merely an electrical installation. It becomes an element of environmental therapy whose role is to support the body’s natural regenerative mechanisms.

An increasing number of hospitals in Europe and North America now incorporate this philosophy at the earliest design stages, combining access to natural daylight with dynamic artificial lighting systems that follow the biological rhythms of patients and staff.

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Key takeaways

Light directly influences the human circadian rhythm.
Proper lighting can support patient recovery and regeneration.
Poorly managed light exposure can significantly reduce sleep quality.
Human Centric Lighting is becoming a standard in modern healthcare facilities.
Evidence-Based Design recognizes light as an essential component of the therapeutic environment.

FAQ:

How does light influence the healing process?

Light affects not only vision but also physiological functioning. Properly designed lighting supports circadian rhythm regulation, improves sleep quality, regulates melatonin and cortisol secretion, and can accelerate recovery. Research suggests that access to daylight and biologically effective lighting may improve patient well-being and support faster rehabilitation.

What is a circadian rhythm and why is it important in hospitals?

The circadian rhythm is the body's internal biological clock operating on an approximately 24-hour cycle. It regulates sleep, wakefulness, metabolism, body temperature, and hormone production. In hospitals, limited exposure to natural daylight can disrupt this rhythm, negatively affecting recovery and overall health outcomes.

Why can hospital lighting interfere with sleep?

Many healthcare environments expose patients to nearly constant lighting levels throughout the day and night. Without clear differences between daytime and nighttime conditions, the body struggles to regulate melatonin production, leading to difficulties falling asleep, fragmented sleep, and reduced rest quality.

What is Human Centric Lighting (HCL)?

Human Centric Lighting (HCL) is a lighting design approach that considers the impact of light on health, well-being, and biological rhythms. HCL systems dynamically adjust light intensity and correlated color temperature throughout the day to mimic natural daylight patterns.

What are the benefits of biologically effective lighting in healthcare facilities?

Key benefits include:

Improved patient sleep quality
Better support of circadian rhythms
Reduced disorientation and post-operative delirium
Faster physiological recovery
Enhanced well-being
Improved working conditions for healthcare staff
Reduced fatigue during shift work

Can light affect melatonin levels?

Yes. Exposure to light, particularly light with a high blue-light content, suppresses melatonin production. This effect is beneficial in the morning because it increases alertness. However, excessive exposure in the evening may delay sleep onset and disrupt natural circadian rhythms.

Which hospital departments benefit most from circadian-supportive lighting?

The greatest benefits are observed in:

Intensive care units (ICUs)
Geriatric wards
Psychiatric units
Rehabilitation departments
Post-operative recovery rooms
Emergency departments
Operating theatres
Diagnostic imaging facilities

These areas often have limited access to natural daylight and prolonged occupancy periods.

What are ipRGC cells and why are they important in lighting design?

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are light-sensitive retinal cells containing melanopsin. They transmit information about environmental light levels to the body's biological clock and play a critical role in regulating circadian rhythms. Their discovery demonstrated that light affects much more than vision alone.

What does CIE S 026/E:2018 mean?

CIE S 026/E:2018 is an international standard published by the International Commission on Illumination (CIE). It provides a framework for evaluating the biological effectiveness of light using melanopic metrics and is widely recognized as a key reference for circadian lighting design.

How does lighting affect healthcare professionals?

A well-designed lighting environment can improve concentration, reduce fatigue, and support personnel working in shift-based schedules. This is especially important in 24-hour healthcare facilities, where staff are frequently exposed to circadian disruption.

Is daylight more important than artificial lighting?

Daylight remains the most powerful synchronizer of the human biological clock. However, in many healthcare settings sufficient daylight exposure cannot always be achieved. In such cases, advanced dynamic lighting systems can partially reproduce natural daylight variations throughout the day.

What is Evidence-Based Design in hospital architecture?

Evidence-Based Design (EBD) is a methodology that uses scientific research to guide design decisions. In healthcare facilities, this means creating spaces that support patient recovery through optimized acoustics, air quality, ergonomics, access to nature, daylight, and carefully designed lighting systems.

Can lighting influence the length of hospitalization?

A growing body of research suggests that environments supporting recovery, including access to daylight and circadian-friendly lighting, can positively affect patient comfort and treatment effectiveness. As a result, lighting is increasingly recognized as an important factor within modern therapeutic environments.

What characteristics should modern healthcare lighting provide?

Modern hospital and clinical lighting should:

Comply with applicable lighting standards
Provide high visual comfort
Minimize glare
Deliver excellent color rendering
Support circadian health
Allow control of light intensity and color temperature
Promote the well-being of both patients and healthcare professionals

Will biological lighting become a standard in future hospitals?

All indications suggest that it will. The growing body of research on light's influence on health, combined with rapid advances in Human Centric Lighting technologies, is making biological effectiveness an increasingly important consideration in the design of future healthcare facilities.