In response to advances in scientific research, the CIE published CIE S 026/E:2018, introducing methods for assessing the biological effects of light through so-called melanopic quantities.
The best-known parameter today is melanopic Equivalent Daylight Illuminance (mEDI), which measures the biological effectiveness of light relative to daylight.
In practice, this means that two light sources with identical lux values may have significantly different mEDI values and therefore different impacts on the human body.
This represents one of the most significant developments in lighting design in recent decades.
As a result, lighting designers increasingly evaluate not only illuminance levels but also the biological potential of light.
Importantly, melanopic metrics do not replace traditional lighting parameters. Both approaches complement one another.
In practice, Human Centric Lighting is built on three fundamental principles.
- Dynamic illuminance levels
Natural lighting conditions are never static. Light intensity changes continuously from sunrise to sunset, reaching its highest levels around midday.
For many years, hospitals relied on almost constant lighting levels throughout the day and night. Today, this approach is gradually being replaced by dynamic lighting systems.
Intelligent control systems can automatically increase illuminance during the morning and daytime hours and progressively reduce it in the evening.
This supports circadian rhythm synchronization without requiring manual intervention by staff.
- Dynamic correlated color temperature (CCT)
The second key factor is changing the color temperature of light.
Daylight naturally shifts in color throughout the day, from warm tones at dawn, to cooler light around midday, and back to warmer hues in the evening.
Modern Tunable White luminaires can replicate these changes.
Typical lighting strategies include:
- higher color temperatures during morning and late morning hours,
- neutral white light during the day,
- warmer light in the evening,
- very warm light during nighttime scenarios.
This approach helps reduce melatonin suppression during the night while still enabling necessary care activities.
- Direction of light distribution
This aspect is often overlooked in lighting design.
Lighting standards primarily focus on illuminance levels on the working plane. From a biological perspective, however, the amount of light reaching the user's eyes is much more important.
As a result, designers must ensure adequate illumination of:
- vertical surfaces,
- users’ faces,
- the overall visual field.
For this reason, modern healthcare facilities increasingly use solutions such as:
- indirect lighting distribution,
- illuminated walls,
- luminaires with a high upward light component,
- soft luminance distributions that reduce glare.
Such an approach improves both visual comfort and the biological effectiveness of the lighting environment.
One of the most important tools in contemporary healthcare lighting design is Tunable White technology.
These luminaires allow smooth adjustment of color temperature while maintaining high lighting quality. Their flexibility enables the creation of lighting scenes tailored to the time of day, medical procedures, and users’ needs.
Several standard lighting scenarios can be distinguished.
Morning scene
Brighter, cooler light that supports wakefulness and staff alertness.
Daytime scene
Lighting optimized for everyday medical tasks while maintaining a high level of visual comfort.
Evening scene
Gradual reduction of illuminance and color temperature to prepare the body for rest.
Night scene
Low-level lighting that enables patient observation and safe movement of medical staff while minimizing disruption to patients’ biological rhythms.
Human Centric Lighting would not be possible without appropriately designed control systems.
Modern healthcare facilities increasingly use digital lighting management systems such as DALI-2, enabling automatic execution of lighting scenes aligned with daily schedules.
Integration with a Building Management System (BMS) allows lighting to respond to:
- daylight availability,
- occupancy,
- department functions,
- staff schedules,
- emergency scenarios.
As a result, lighting becomes much more than a passive electrical installation. It evolves into an intelligent component of healthcare infrastructure.
It is important to emphasize that Human Centric Lighting does not replace existing lighting standards.
The primary reference document remains EN 12464-1 “Light and Lighting – Lighting of Workplaces – Indoor Workplaces”, which defines requirements for illuminance, uniformity, glare limitation (UGR), color rendering, and other parameters affecting visual performance.
At the same time, the standard does not define requirements related to the biological effects of light.
This means that a lighting design may fully comply with all standard requirements while still failing to adequately support users' circadian rhythms.
In professional practice, both approaches should work together. Standard lighting parameters ensure visual performance and safety, while Human Centric Lighting principles contribute to health, recovery, comfort, and overall well-being.
The integration of technical requirements with the latest knowledge in chronobiology is shaping the future of modern healthcare lighting design.