Yoelit Hiebert
EDN
The concept of human-centric lighting (HCL) has its origin in the discovery in the early 1920s that the human eye has a third type of receptor complementing cones and rods, which allow us to perceive color and light levels. Eyes are also equipped with photoreceptive retinal ganglion cells, which affect circadian rhythms. These cells communicate with the body's center of physiological control and are especially sensitive to blue wavelengths of the visible light spectrum, which happens to be a significant component of sunlight (Figure 1).
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| Figure 1. | Representative spectral power density of daylight - blue wavelengths are a significant component, especially on clear days. (Source: Tech Sensitive). |
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The 1980s saw the initiation of research into human biological response to light level and wavelength with investigations into the effects of lighting on mood, productivity, alertness, and visual acuity, as well as circadian rhythm. This research led us to the understanding that not all white light is equal, that cooler white vs. warmer white not only changes how we perceive our surroundings, but also affects our physiological responses.
It's no accident that upscale restaurants tend to be dimly lit with warm white light to both make our food (and us) look better and to encourage a sense of relaxation and leisure (perhaps leading to a higher tab).
A concept intrinsic to HCL is varying the quality of illumination from light fixtures to mimic the different quality of natural light at different times during the day. LEDs are the first commonly available light sources that are adjustable – readily able to change both output spectrum and light level, which uniquely positions LEDs to optimize HCL in a wide range of facilities and environments.
The most common application of HCL principles thus far is probably in air travel – it seems that all new commercial aircraft feature LED interior cabin lighting, often set to a pleasant purple hue. Passengers might also notice that cabin lighting changes during the course of a long flight; purple or blue during boarding, warmer white at meal time, and deep purple to help encourage sleep. And to help minimize jet lag, the cabin lighting might slowly transition to simulate sunrise as the flight nears its conclusion.
But it is in hospitals and assisted living centers that the potential of HCL is best realized so far. HCL is believed to help maintain the natural sleep cycle; reduce patient anxiety; promote healing; maintain alertness of nurses and other caregivers working at night; and improve visual acuity during examinations.
This is accomplished through programmed and on-demand lighting of varying spectra, depending upon the desired result. For example, to promote a normal sleep cycle, patient room lighting might operate on a schedule that provides cooler white light during the day with a transition to warmer white in the evening.
For examinations or emergencies, however, the lighting could be manually changed to provide a greater degree of visual acuity. More sophisticated HCL designs might divide a space into zones, with a programmed lighting protocol for each depending on the amount of daylight in the zone and the intended use of that portion of the space (e.g., the visitor area of a hospital room vs. the patient bed or the central nurses' station vs. floor hallways).
Other environments where HCL concepts are currently being applied include educational settings, where, for instance, lighting is set to warmer white at nap time; and office environments, where cooler white overhead lighting is combined with individually adjustable task lighting to help encourage alertness, productivity, and visual comfort.
An HCL implementation combines products specifically designed for this functionality with a significant degree of lighting system design including both automated and manual controls incorporated into a top-level network.
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| Figure 2. | Ledmotive HCL LED module Source: Ledmotive | |
For example, Ledmotive's HCL system (Figure 2) includes an LED module that uses seven independent color channels to reproduce any spectral configuration, statically or dynamically, with essentially no UV or IR emissions (Figure 3). The modules, incorporated into luminaires, are then connected via a bus to a hub for communication with a lighting network controller or building management system.
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| Figure 3. | Spectral power distribution of seven independent channels of the Vega 07 module. (Source: Ledmotive). |
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The potential for HCL to change our lives for the better is an exciting prospect, but it's important to keep in mind that while there's a general and growing consensus about how light spectra and levels affect the human body, individual results are impossible to predict. Nonetheless, according to BIS Research, the market for HCL products and systems is estimated to reach nearly $4 billion by 2024.
