The LED Driver's Role In Human-Centric Lighting

September 7, 2021 Paula Santa Cruz

How can the luminaire manufacturers and lighting professional’s choice of driver support the many visions of Human-Centric Lighting? 

There’s one thing that most lighting professionals can agree on—no one is sure of what Human-Centric Lighting (HCL) is in practice. It’s true that the philosophical underpinning of Human-Centric Lighting is a belief that lighting should promote the health, well-being or comfort of users. For some people, this also means that Human-Centric Lighting should mimic natural light sources such as sunlight. 

There are also competing visions on how to design lighting for health or well-being. The priorities of specifiers and users also varies based on the setting. The designer’s view of ‘Human-Centric’ is greatly influenced by whether their lighting scheme is for hospital patients, school children, office workers, or assembly-line technicians in a factory. 


Challenges For Luminaire Manufacturers And Lighting Professionals

This poses a problem for Luminaire Manufacturers and lighting professionals alike. On the one hand, manufacturers generally like to make a strategic choice of driver supplier—and even of a family of driver products. The selection of a single or primary driver supplier is advantageous in reducing the effort and time involved in vendor and product qualification. It also means that the manufacturer’s design engineers and installers only need to familiarize themselves with one set of features, technologies, programming tools and so on. 

For lighting and other specifying professionals, the fast-changing view in the market regarding how to meet the demand for a Human-Centric lighting element means that the functional requirements of the driver are almost certain to change over time—varying greatly from installation to installation. 

The challenge becomes two-fold:
  1. How can a single driver choice or driver supplier remain consistent while the luminaire’s specifications are ever-changing? 
  2. How can Luminaire Manufacturers future-proof their preferred driver supplier while taking account of the different implementations of Human-Centric Lighting? 


The LED Driver's Role In A Human-Centric Lighting Scheme

Part of the reason why the term ‘Human-Centric Lighting’ is so hotly contested is because the idealized natural lighting theory conflicts with its implementation in real-world lighting schemes. 

At its most extreme, Human-Centric Lighting is the exact replication of the spectral power distribution of light’s changes throughout the day and firelight at night. All of these are the light sources that shaped and influenced human evolution. 

Human-Centric Lighting sources mostly operate alongside other sources such as ambient daylight, computer monitors and task lights—as well as reflected light from surfaces. In practice, it’s very difficult to control the light to which users are exposed at the most precise spectral level. 

Lighting designers today are focusing on the broad effects that the dominant light sources in a space can have. These effects are generally categorized as one or more of: 

  1. Visual Effects: Colors in an art museum rendered in a way which is faithful to the vision of the artist (see Figure 1) 
  2. Biological Effects: The lighting’s ability to match or distort the natural circadian rhythm of the user
  3. Emotional Effects: Invoking feelings of calm and relaxation in a home’s living room at night or pumping up the trainers’ feeling of high energy in a gym

Now the ultimate question—what is the role of the LED driver? The driver is one of the components that works with the remainder of the components in a luminaire. Lighting Manufacturers implement all components in a carefully crafted lighting design—producing the effect. 

Fig. 1: Museum Voorlinden in the Netherlands. The intensity of the LEDs’ light is dynamically adjusted in response to the level of daylight with SOLOdrive drivers.


Common Human-Centric Lighting Requirements 

The common requirements include the light’s color control and brightness across multiple LED channels. Each relationship between the dimming and color controls is different. The color ranges rendered in a single installation also varies widely. For example, you may specify 1800K CCT for a cozy living room’s CCT in the evenings while the daytime may call for a more lively feeling induced by a 4000K output. 

Programming Human-Centric Lighting functions requires system intelligence. This intelligence is not only confined to the LED driver. Another option is a simple microcontroller that offers various control outputs. This adjusts the duty cycle of multiple channels of LEDs that can support various control interfaces and is backed by user-friendly programming tools.

A different way to achieve the same outcome is with a smart color sensor. This measures the brightness and color of light emitted and creates a closed-loop feedback scheme to control the power to multiple LED channels. 

Regardless, there’s still a driver that powers the LEDs. The use of a microcontroller or smart sensor involves adding an extra component and increasing the complexity and cost of the system. 

This is why an intelligent driver is the best way to perform the color and brightness control in a Human-Centric light. The driver is always connected to power, to the control interface and the LEDs. 

Adding intelligence to the driver, the luminaire gains the flexibility to handle the varying ways in which a lighting designer or specifier implements human-centric lighting in a specific application, depending on whether visual, biological or emotional effects are most important to the user. 


(New) Intelligent LED Driver Key Features 

Implementing the necessary color control and dimming functions for Human-Centric Lighting involves the following new driver capabilities:
  • Two or more outputs for multiple LED channels
  • High-performance dimming supported by a variety of selectable dimming curves
  • Color Awareness to convert the control system’s instruction to an accurate color output from the LEDs within the fixture
  • Compatibility with the control interface range. This ranges from a 0-10V scheme, to DALI and DMX and up to the latest user-friendly controls such as Casambi and Bluetooth® Low Energy networking


High Performance Dimming 

Since the goal of all Human-Centric Lighting is to protect users’ health and well-being, a driver’s key requirement is ensuring flicker-safe dimming. Visible flicker is an unintended consequence of a luminaire’s output that causes discomfort to users. Modern research identified a number of harmful and unpleasant side effects of non-visible flicker at low frequencies. 

A flicker-safe driver ensures that the LEDs’ frequency switches when dimmed and maintains safe lighting at high levels—even when performing deep dimming down to 1% and below (see Figure 2).

A selectable dimming curve range is also a crucial requirement of Human-Centric Lighting. It enables the Luminaire Manufacturer to meet the various dimming requirements of different lighting designs with a single driver. 

Fig. 2: An eldoLED report showing how a driver complies with best practice for flicker-safe dimming as required by the IEEE P1789 standard


Programmable Color Control 

Tunable White lighting—variable dimming of two or more channels of LEDs at different CCTs to hit a target combined CCT value—is widely used today. 

The challenge for a Luminaire Manufacturer implementing a single driver across an HCL scheme is achieving color consistency across the range of selectable CCT values and luminaires. All without implementing frighteningly elaborate processes for calibrating, binning and mixing LED units. 

The provision of a driver’s ‘color awareness’ eliminates this problem and enables the Luminaire Manufacturer to program LED data into the driver, set the required CCT values and then rely on the intelligence in the driver to produce the correct color output for any given installation. 


Real-World Example In Human-Centric Lighting: 't Handelshuys

Fig. 3: 't Handleshuys is a co-working space for multiple business types in the Netherlands

A recent installation in a commercial building in the Netherlands provides an example of the way that a single intelligent driver can meet a variety of requirements for human-centric lighting.

‘t Handelshuys—located in the town of Uden—is a mixed-use facility for small businesses like:

  • Art studios and study centers 
  • Teaching spaces for school-aged children 
  • Offices 
  • Workshops

Every working space requires different driver functions for the users’ varying lighting needs. The artist adjusts the light to give high brightness when the students are engaged in a creative workshop and to provide an appropriate daylight color temperature when painting. On the other hand, the teacher values dimming while the students present—helping reduce public speaking-related insecurities. 

Office workers take advantage of the Casambi smartphone app—which provides intuitive wireless control—to adjust the color temperature throughout the day to align with natural daylight. Here are examples of the three dimensions of Human-Centric Lighting: the visual, the emotional and the biological. 

The ‘t Handelshuys lighting scheme implements all these variations of color and intensity with around 1,000 units of a single luminaire. Users enact the different lighting effects by changing the settings of the luminaire’s eldoLED DUALdrive driver. This driver includes various programmability and configuration capabilities including: 

  • LightShape technology for implementing Tunable White and Dim to Warm effects (see Figure 4). The color awareness provided by LightShape is easily programmable at the factory, by the Luminaire Manufacturer or on-site by the installer
  • Hybrid HydraDrive technology for flicker-safe dimming and Dim to Dark effects. The DUALdrive LED driver dims down to 0.1%
  • Casambi compliance that provides users with convenient color and dimming controls via their smartphone

Fig. 4: A tunable white installation with LightShape allows brightness and color temperature to be adjusted independently of each other

The example of ‘t Handelshuys demonstrates how manufacturers can reconcile their desire for a single driver for all luminaires with the need to meet widely varying implementations of the contested concept of ‘Human-Centric Lighting’.




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