Artificial light in a natural way: human centric lighting

If you’ve ever noticed that you tend to feel energized and drowsy around the same times every day, you’ve identified your circadian rhythm. Also known as the sleep/wake cycle, this is essentially our 24-hour internal clock.

The brain’s hypothalamus controls our circadian rhythms, but they are also directly affected by light. When it’s dark, your eyes send a signal to the hypothalamus that it’s time to feel tired. Your brain, in turn, sends a signal to your body to release the hormone melatonin, which makes you feel sleepy. That’s why your circadian rhythm tends to coincide with the cycle of daytime and nighttime (and why it’s so hard for shift workers to sleep during the day and stay awake at night).

The need for daylight is a fundamental part of human biology. We evolved to spend the majority of our time outdoors, which means exposure to natural light has a whole host of health benefits, from promoting better sleep to improving our mood. It regulates the levels of vitamin D, serotonin and melatonin in our bodies, and promotes healthy eye development.[1]

The business benefits of exposure to natural light are also clear. Office workers who sit near windows sleep on average for 46 minutes longer than those who don’t.[2] While workplaces with good levels of natural light benefit from productivity gains between 3% and 40%.[1]

Yet despite these known benefits, the majority of us spend a significant proportion of our days indoors exposed to artificial light. Unlike natural daylight, artificial light doesn’t vary in color temperature or intensity over the course of the day.

In general, earlier in the day our bodies should be exposed to a higher proportion of particular short-wavelength blue light and stronger light intensity. This enhances alertness and performance and has a powerful effect on resetting the circadian clock.

As evening draws in exposure to blue light should be avoided, to allow our bodies to feel sleepy. This is one of the reasons both iPhones and Android phones now offer red shift modes after sunset.

“We are exposed to artificial light sources all day long,” says Sarah Klein, one of our lighting researchers. “Depending on the specific light source it can have a lot of blue light in it, especially when we talk about screens. That actually means that it's helpful in the morning and during lunchtime, but it's certainly not helpful if you use it in the late afternoon or in the evening. It leaves us far too awake, which results in a lack of sleep and harms our cognitive performance.”

Given that so many of us are regularly spending more time in artificial light than natural daylight, creating artificial lighting which reflects the natural changes in daylight over the course of the day could make a huge difference to our health and wellbeing.  

The known benefits of natural light prompted NASA scientists to begin studying whether lighting on the International Space Station (ISS) could be affecting the performance of their astronauts.

Crewmembers on the ISS experience sunrises and sunsets in rapid succession – about 16 “sunsets” per day because the space station circles Earth once every 90 minutes. This departure from the cycle of light and dark that astronauts were used to at home was thought to be disrupting their circadian rhythms – in turn, affecting their performance.

A NASA study was set up to coincide with a lighting ‘makeover’ on the space station.[3] The fluorescent lights on the station were replaced with a new system of solid-state light-emitting diodes (LEDs) which had been programmed to shift color and intensity over the course of the day, mimicking the patterns that we would experience on Earth.

This concept of human centric lighting, as showcased in NASA’s study, is now gaining increasing traction back down on Earth. The idea behind it is the same – but for buildings, not space stations – to create lighting which naturally adapts over the course of the day to expose people within the building to a range of white light which echoes the natural daylight outside.

As the technology has developed, it has shown strong potential as a safe, non-pharmacological way to counter disruption of circadian rhythm and improve the health and wellbeing of anyone who’s not exposed to the optimal levels of natural light, from shift workers to people who are stuck in an office for most of their day.

The effect of these types of lighting systems is impressive. A recent study conducted in a German supermarket found that after installing human centric lighting, sales increased by 28%. While the number of employees taking sick days fell by 35%. Customers reported an improved sense of wellbeing and a better atmosphere while shopping. And employees also reported better wellbeing scores and improved sleep.[4]

“We believe dynamic light systems can make a huge difference in a number of scenarios,” adds Klein. “For example, in airplanes it can help travelers cope with jet lag, in hospitals it can make people heal faster and in warehouses and factories it can help shift workers adjust to working at night.”

LEDs are already an everyday part of life. They have several clear advantages in comparison with conventional light sources. They save energy, are eco-friendly due to their long lifetime, and don’t contain mercury. But they also have specific properties that make them perfect to deliver the color variations needed for human centric lighting.

White light is a combination of all colors in the visible spectrum. However, LEDs are based on single semiconductor chips that emit a single color of light, meaning it’s not possible to generate white light directly. To achieve white light, additional light-converting materials, phosphors, are needed.

Phosphors are micro-sized inorganic crystals and contain rare earth metals like yttrium and lutetium. Usually, a blue LED is combined with one or more light-converting materials. The converted light can produce any single color or a combination of colors and can generate all variations of white light – making them ideal for delivering human centric lighting that shifts colors over the course of the day.

The quality and properties of the lighting material determine the efficiency of the LED and enable different color points – varying the appearance of a white light source, for example, from cold and neutral to warm white.

Our partners wtec have developed a smart version of human centric lighting (Network-Powered Lighting) as part of their smartengine building control technology. This is already installed in more than 15 million square feet (1.5 million square meters) of commercial space worldwide, in offices at Blue Chip companies, government buildings, schools and universities, retail stores, production sites, and data centers. Not to mention our own Innovation Center in Darmstadt.

But smartengine isn’t just about improving the wellbeing and health of building occupants.

“It’s the only technology that combines the concept of human centric lighting and the highest levels of energy efficiency,” says Daniel Stephen Massey, Managing Director at wtec GmbH. “LEDs are very efficient – when they are powered by a low voltage constant current. In buildings though, LEDs are usually being powered by AC power (100-277V), which is stepped down at each LED, resulting in high energy loss and heat emission.

“smartengine provides Network-Powered Lighting that solves this issue by distributing the exact amount of low voltage power required to each individual LED based upon selected lighting scenes, surrounding light levels and continuous dimming for ‘daylight harvesting’. Human centric lighting doubles the number of LEDs in a light, as both warm and cool white LEDs are installed to smoothly mix color temperatures matching the sun's daylight curve. As LEDs become more efficient at lower power inputs, doubling them results in even less power required at the same light levels when performing human centric smart lighting.”

We’ve found that at our Innovation Center, energy consumption is an incredible 1.9 watts per square meter, a tenth of what conventional lighting systems require, thanks to the intelligent control system,
which will equate to an annual saving of 92.6 tons of carbon dioxide emissions.

So, what does this mean for the future of buildings and architecture?

We believe that eventually all buildings will be smart, reacting autonomously to the needs of the users. Lighting with LEDs will be ubiquitous, helping people feel healthier and perform better in a whole variety of different situations.

References:

[1] https://www.eco-business.com/opinion/why-natural-light-matters-in-the-workplace/
[2] https://www.worldgbc.org/better-places-people/green-healthy-work-spaces
[3] https://www.nasa.gov/mission_pages/station/research/let-there-be-better-light
[4] https://www.luxreview.com/2018/11/08/human-centric-lighting-boost-supermarket-sales-by-28/