Why Human-Centric Lighting Matters

Today’s LED and lighting-control technologies are making it possible to do much more with lighting than illuminate a space.

The A.T. Kearney 2015 study shows a number of micro and macro benefits for the medical sector. For a hospital with 1,000 beds and 1,500 employees, the study indicates that human-centric lighting can increase capacity utilization through higher attractiveness for new patients and can cut treatment costs through reduced treatment times. In addition, sick leave taken by care staff could go down, and employee satisfaction and therefore staff retention could go up.

By Alberto Pierotti, LEDVANCE

“Human-centric lighting” is an emerging best practice in lighting design that leverages the full capabilities of the LED light source to serve occupant needs in terms of visual and non-visual well being. It may have the ring of a marketing buzzword but, in reality, it is founded on solid science, actionable, and shown to produce tangible positive outcomes. In short, it is a revolution in how lighting systems are designed to serve people.

For most of history, lighting was designed without knowledge of the non-visual effects of illumination. As a consequence, lighting systems were fixed in light output and color once installed, and lighting design focused illumination on horizontal work surfaces.

Then everything changed:

• LED systems offered easy and cost-effective dimming in addition to the ability to adjust shades of white light, emit saturated colors, and even produce unique spectral recipes for special applications.

• Lighting-design best practices recognized the importance of vertical illumination to creating bright, open, visually comfortable spaces.

• Scientists discovered the presence of photoreceptors in the eye that connect to the body’s circadian system, which regulates bodily functions—such as the sleep-wake cycle—based on 24-hour cycles, or circadian rhythms.

This has given rise to the unified concept of human-centric lighting (HCL), which LightingEurope, Brussels and the International Association of Lighting Designers, Chicago, jointly defined as lighting that “supports health, well-being, and performance of humans by combining visual, biological, and emotional benefits of light.” Visual benefits include the industry’s traditional focus on good visibility, visual comfort, safety, and orientation. Biological benefits include alertness, concentration, cognitive performance, and stable sleep. Emotional benefits include improved mood, increased energy, better relaxation, and impulse control.

LightingEurope quantified the economic value of these benefits for various building types in a landmark 2015 study conducted by A.T. Kearney, Chicago, in which HCL was estimated to offer significant potential cost savings related to enhanced worker productivity and fewer errors, absences, and accidents.

According to the “SSL-erate” European Union project, exposure to light similar to natural daylight at the right time can help improve the mood of residents in retirement and care homes as well as patients in hospitals, helping prevent depression and reducing anxiety in patients in the early stages of dementia.


What makes HCL possible is technology properly applied to spaces through design best practices that, in turn, are promoted by standards.

First, let’s look at technology. Traditionally, aside from special applications such as boardrooms, lighting systems were installed as static light producers. After installation, light output and color quality more or less remained fixed. Aside from changing failed lamps, it was largely forgotten.

With LED technology, this has changed.

Most LED luminaires are either dimmable as a standard feature or a standard option, with a negligible cost premium. This dimming provides inherent flexibility in adjusting light levels in response to daylight or occupant needs. Further, it allows control of the luminaire’s color output through:

• separately dimmable arrays of warm- or cool-white LEDs
• color-mixing arrays of red, green, blue, and amber LEDs
• adding separately dimmable LEDs to white LEDs.

These approaches provide a range of capability from limited adjustment of correlated color temperature across a set of channels up to producing any shade of white light (from very cool/bluish to very warm/reddish) plus a virtually limitless range of saturated colors.

Various general lighting products are now available that provide manual and programmable color tuning; imitate the warm color of incandescent lamps while being dimmed; and/or offer precise color matching between LED products and calibrate to maintain constant color output over their life. What all of this has in common is that how a space appears depends on how it’s lighted. Change the color quality of the light source, and you change how the space appears, with associated effects on visual rendering, perception, and mood.

Now let’s switch to application and design. These capabilities could be applied in many ways, ranging from the cosmetic to utility:

• changing color output to accommodate changing retail displays and to ensure merchandise appears visually vibrant and appealing

• signaling time for different activities in a classroom

• using saturated color to indicate occupancy and availability of private office users

• changing color, or CCT (correlated color temperature) to adapt lighting to different situations for the medical environment, e.g., examination rooms versus reducing patient stress in a hospital

• tuning color to saturated colors to transform a functional space into an entertainment venue

• altering color output to precisely match space decor after final materials and furnishings are installed in a hospitality space, with future retuning available if new furnishings are installed

• adjusting white-light temperature to adapt a restaurant space based on time of day, such as cool during business luncheons to warm during evening dining.

In HCL, the greatest value of dimming and color control may be found in circadian-lighting design. Scientific research has shown that specialized photoreceptor cells in the eye are connected to circadian functions, and has identified spectra, quantity of light, duration, and timing capable of producing circadian stimuli. From this understanding came actionable approaches to design, with good circadian design typically focused on:

• Spectral distribution, or saturation of specific wavelengths in the visible light spectrum that we associate with the light being warm or cool in appearance. Circadian regulation is most responsive to short-wavelength light (460 nm, which is in the blue range of the visible spectrum).

• Spatial distribution, which defines where the light emitted by a luminaire falls in the observer’s field of view (FoV). For circadian response we want a sufficient quantity of light on the upper quadrant of the environment for sufficient periods of time during the day. Equate this to the outdoors, where the sky occupies the top section of our FoV. This requires vertical illumination (uplighting walls and ceilings, or workstation luminaires), in addition to the standard work-surface-targeted lighting devices.

• Temporal distribution, which simply means the right light (in terms of CCT and intensity) at the right time of day. A circadian lighting solution ideally exposes users to high-intensity, short-wavelength-heavy light in the morning, which can taper to lower light levels of long-wavelength light in the afternoon.

Daylight is ideal, though it is not always available, and the electric lighting system can work with daylight for an optimal solution.

Finally, this brings us to standards. Best practices for circadian lighting are still emerging, such as International Standard DIS 026/E:2018, which is being considered by the International Commission on Illumination, Vienna, Austria. This standard would define spectral sensitivity, quantities, and metrics to describe light radiation for its ability to stimulate each of the five types of photoreceptor cells in the eye that produce non-visual effects in humans.

One standard that is oriented toward application and actionable today is WELL, a rating system focused on evaluating how effectively a building supports human health and wellness. Launched in 2013 by the International WELL Building Institute, New York, this rating system awards points for various building features and practices. This includes lighting, notably circadian lighting, visual comfort, glare control, color quality, automatic dimming and shading, and daylighting.

For circadian lighting, WELL establishes four types of environments and requires a minimum level of light capable of producing circadian stimulation. Measured at the eye level, this light is measured as equivalent melanopic lux, an alternative metric to footcandles/lux that is weighted to non-visual photoreceptors.

A key enabler for HCL strategies is lighting controls, a segment of the lighting industry undergoing its own digital revolution. These are the sensors, controllers, apps and programs, and communication technologies that enable manual and automatic control of light and color output.

Because LED lamps and luminaires are already electronically controlled, they are inherently compatible with intelligent systems capable of sophisticated control and data collection from sensors. Using this data, operators can optimize energy cost savings while gaining valuable insights into user lighting preferences and satisfaction.

Human-centric lighting (HCL) uses smart-controllable LED lighting systems to simulate the characteristics of natural daylight, giving something back to us that we often lack indoors. Field studies show that all age groups can benefit from HCL solutions.

Realizing HCL

What does this mean for designers?

Rather than a fixed utility used to produce the commodity of light, lighting has become an asset offering far greater value. There is no single lighting solution that is ideal for every client and application, however. What leading commercial architects and designers are doing is looking beyond traditional design thinking and changing the conversation they’re having with their clients.

This requires education that in turn will fuel a different conversation about lighting—not one limited to light levels and watts, but one that incorporates all of lighting’s current possibilities and best practices. From color tuning and dimming to more effective ways to light spaces to data collection, today’s lighting technology, application, and thinking has taken the category far beyond its static traditions, with far more value on the table than simple vision.

Alberto Pierotti is head of R&D and Smart, USC at LEDVANCE, Beverly, MA, makers of Sylvania general lighting products in the US and Canada. At LEDVANCE, he is leveraging the company’s century of expertise in light to chart the path into the intelligent, distributed-lighting systems of the future. For more than 20 yr., Pierotti has been involved in every step of the product-development process in fields spanning from medical devices to capital equipment, and from wearable consumer electronics to architectural lighting.

International Association of Lighting Designers
A.T. Kearney
International Commission on Illumination
International WELL Building Institute

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