Smart light's bright future

-December 02, 2014

This article is part of EDN and EE Times’ Hot Technologies: Looking ahead to 2015 feature, where our editors examine some of the hot trends and technologies in 2014 that promise to shape technology news in 2015 and beyond.

Imagine a world where the lights in our homes and workplaces help keep us healthier, more productive, and happier. In this world, students attend classes in rooms with lighting systems designed to help them learn more quickly and stay more alert. Hospitals use light in unique ways, flooding the rooms and halls with spectra designed to help accelerate recovery from surgery and rally a patient's natural healing capabilities. Does this sound like science fiction?  Think again. It's human-centric lighting.

For those not familiar with this new, and seemingly vague, term, human-centric lighting (HCL) is a technology born from the convergence of LED technology, smart objects, and new findings on how light can be used to enhance our comfort, productivity, and health. Such lofty goals may seem like a tall order for a humble quantum well device, but its efficiency and unique spectral capabilities are already being harnessed to serve our growing understanding of the profound effects that light has on the human endocrine system, our metabolism, and even our brains.

Human-centric lighting can be used to enhance the comfort, functionality, and beauty of the spaces we live and work in.  Source: Soraa Lighting

The power of light

HCL has three basic tools at its disposal: precise control of the light source's spectral content, its intensity, and the ability to adjust these two characteristics over time. If you have any doubts about the power of light to affect people's minds and bodies, ask someone who uses a light source that mimics the sun's characteristics to combat the depression and physiological effects caused by Seasonal Affective Disorder (SAD). Exposing people to lights that mimic the intensity and spectral qualities of the sun for even a few minutes have proven to be a reliable, drug-free way to help fight the "winter blues," a series of changes to the body's metabolism and brain activity, brought on by the shorter days and dimmer, redder light which occurs during the winter at higher latitudes.

Another relatively straightforward application of HCL already in development is chronobiologically adapted aircraft cabin lighting systems that help minimize the effects of jet lag for passengers hopping across multiple time zones. These systems use carefully sequenced levels of warm-white light to stimulate melatonin production and promote restful sleep during long, overnight flights. Toward the end of the journey, the systems provide physiological cues to help passengers re-synchronize with the "local morning." As the cabin is gradually filled with cooler (bluer) light, passengers' bodies respond by suppressing melatonin production and raising blood levels of serotonin and other substances which promote wakefulness and alertness.

Airlines are already using chronobiologically-adapted cabin lighting to help cushion the impact of crossing multiple time zones. Source: Osram

But these applications only scratch the surface of what may be possible. Studies conducted as early as the 1990s indicate that your eyes may not be the only part of your body that can change your physiology when exposed to light. For example a study conducted in 1998 indicated that people's biological clocks could be advanced or delayed up to three hours by shining a bright light on the backs of their knees (detailed in the a 1998 NY times story "Study Offers Surprise on Working of Body's Clock"). Although unexplainable at the time, scientists are now beginning to understand the mechanisms which allows light to trigger the reset mechanism for the body's master biological clock. Other studies show promising evidence that the right combination of spectrum intensity and timing can be used to help maintain alertness or reduce stress and even rally the body's immune system and healing responses.

Smart light in action

So how, exactly would a light make you smarter, happier, or healthier?  Rick Hamburger, director of product marketing at Philips LumiLEDs may have at least some of the answers. The dimmable, color-tunable troffer light in the video below was created in anticipation of a day in the not-so-distant future when products like this will be routinely improving people’s productivity and quality of life in schools, offices, and even hospitals.

The human-centric troffer light demonstrated at LightFair 2013 by Philips LumiLEDs is an excellent example of what a first-generation HCL product might do and what they might look like. Video courtesy of Bourne Digital.

The troffer-style recessed ceiling luminaire contains an array of white and colored LEDs that can be “tuned” to provide a wide range of color temperatures. Thanks to a unique iPod-like touch controller, users can easily adjust both its light level and color value. Hamburger, who cites several studies on the effect of light on human brain function, says that the troffer’s ability to mimic a full range of dawn-to-dusk daylight spectra can be used to promote alertness in a classroom.

Philips is not alone in its claims. Lumitech, a manufacturer of HCL components, says that a survey conducted at the University Hamburg, showed that HCL techniques could improve some students' reading rate by 35% and reduce their error rate by 45%.

There are also several other dimensions to HCL that center around light's ability to enhance visual acuity and color perception. Traditionally, lighting manufacturers would create products that could optimize people's ability to perceive fine details and subtle color variations by carefully controlling light intensity and glare. LED-based light sources can further enhance acuity by producing outputs with precisely controlled spectral profiles which have been shown to be best for a particular application.

Application-specific LEDs are already popular in retail applications. For example, Philips LumiLEDs, Soraa, and several other major LED manufacturers offer white LEDs for which spectrum has been optimized to enhance a specific type of product, such as clothing, jewelry, or food. In fact, grocers can now buy application-specific LED lights with outputs designed to enhance the attractiveness of a specific type of food, such as vegetables and fruits, meat, baked goods, or flowers.

These white phosphor devices offer high-quality light for a specific application but their spectrum is fixed at manufacture. For applications that need flexibility, manufacturers also offer products which use tri-color (red, green, and blue), or quad-color (red, green, blue, and white) LED arrays whose outputs can be "mixed" by varying the intensity of each emitter.

Productizing HCL

Moving from these early examples to mass-market products will probably proceed in an evolutionary manner as manufacturers gradually identify new markets and create the products to address them. In the process, their progress will be punctuated as they address the market resistance created in good part by the significantly higher price of smart, LED-based lighting products.

Steve Kennelly, director of marketing for Microchip Technology's lighting and medical groups, says that it's likely HCL will win acceptance more quickly for industrial, office, and commercial settings where business owners will regard the higher cost of the equipment as an investment. Even before HCL's human factors dividends are factored in, smart, LED-based lighting systems often save enough energy that they pay for themselves in a year or less. 

In these settings, Kennelly expects low-cost embedded controllers, such as Microchip's PIC10Fxx series, to be used in "lumistats," inexpensive, networked lighting controllers that enable people to easily adjust the color, intensity, and other characteristics of an area's lighting system. If necessary, additional components, such as IR motion detectors, temperature sensors, and communication channels can be inexpensively added to these lighting controllers, transforming them into the photonic equivalent of smart thermostats, such as the Nest, which respond to both their environment, and the needs of the people within it.

Human-centric lighting systems in the workplace that mimic natural daylight cycles can improve productivity and comfort. In addition, they can help employees maintain their bodies' circadian rhythms that play important roles in promoting good sleep habits and overall health. Source: Germany's Federal Ministry of Education and Research
Kennelly expects that HCL-capable lighting controls will also be very popular for restaurants and hospitality venues. Its software will include HCL applications, such as routines that transition the dining room's lighting throughout the day, setting the right mood for their customers' breakfast, lunch, dinner, or after-hours activities. Similarly, bars and nightclubs could use smart, human-centric lighting to gradually crank up a party atmosphere as dusk approaches and then gently wind a rowdy crowd back down as closing time draws near.

A new map for a new territory

But, as with any emerging technology, there's still much to learn in the early days of a new era in which lighting systems begin to assume new roles in creating environments that enhance our lives, our work, and the environment. One of the less-obvious challenges the lighting industry faces is the need for better ways to define the quality of light. As our understanding of the complex ways light affects our perception grows, it's become apparent that the color rendering index (CRI), a well-accepted industry standard is, at best a very blunt metric for defining light quality. In fact, it appears to be completely blind to some important issues HCL attempts to address.

Mike Krames, CTO of Soraa, a manufacturer of full spectrum GaN on GaN LEDs, explains his company's solution to the limitations of the CRI metric. "Our work has shown that color rendering breaks down along two orthogonal axes:  accuracy and preference.  The former is fairly straightforward (how accurately are colors rendered compared to a reference illuminant), but has been limited because the CRI metric, designed to measure it, uses a limited number of color samples.  We are working with the IES (Illuminating Engineering Society of North America) to improve CRI, and expect a recommendation to be put forth in early 2015."
Krames also says that additional metrics are needed.  "For example, there is currently no metric for whiteness rendering for materials containing optical brightening agents. This is a critical issue if one wants objects to appear indoors as they do in natural light, e.g., sun or incandescence.  Thankfully, there are products that provide this (e.g., all Soraa products), and the IES has approved a project on a metric for whiteness rendering as well, for which we hope to have a recommendation by the end of next year."   

Also watching:
  • Photonic couture: Clothing with embedded LEDs has been around for quite some time but it's been mostly limited to geekware, novelty t-shirts, and kids' shoes. This is changing, however, as some edgier inhabitants of the high-fashion world have begun to explore the shimmering possibilities that several thousand points of light can bring to the catwalk. It will probably be a couple of years before LEDs and fiber optics begin to appear in off-the-rack evening gowns but, in the meanwhile, they will probably be helping make the lives of our first responders easier and safer. LEDs and fiber optics embedded in the protective outerwear can make it easier for firefighters and rescue workers to locate each other and coordinate their actions. Inexpensive electronics can add moving color and graphics to a turnout, safety vest, or other wearables, enabling it to be used to direct traffic, as an alarm signal, or a backup visual signaling system in the event of radio failure.
  • OLEDs and OLETs: Will this be the year of the OLED? Organic light emitting diodes (OLEDs) have held as many heartaches as they have promises for the SSL community, but this appears to be changing as researchers and gutsier manufacturers have steadily improved their efficacy, lifetime, and manufacturability. But those long-awaited roll-up displays, spray-on room lighting, and other marvels we've been promised have yet to arrive. Nevertheless hopeful rumors continue to abound and new developments, such as organic light-emitting transistors (OLETs), are opening new markets for organic photonics and improving its odds for capturing a meaningful chunk out of the traditional LED market over the upcoming year.    

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