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Human-centric lighting: light up your life

Image credit: Dreamstime

Human-centric lighting (HCL) has been around for a few years, but has only recently become a buzzword in the technology community. What’s it all about? And could it become commonplace in our homes and places of work?

You’re flying like a bird. Slicing through clouds, flapping your arms, feeling the brisk wind on your face. You’re having the most wonderful dream. Relishing the blissful moment. Suddenly, a crow appears out of nowhere, squawking directly into your ear. And it won’t stop. Then you’re ripped from the ethereal sky and land in your bed, jolted awake by the morning alarm.

Waking up in this unnatural way can often leave you bleary-eyed and sleepily hunting for coffee. When you finally get to work after the exhausting commute, you’re left feeling dishevelled and not fully awake all day, no matter how much caffeine you chug.

That is where the apparent power of human-centric lighting (HCL) comes in. According to the LightingEurope industry association, HCL supports health, wellbeing and performance of humans by combining visual, biological and emotional benefits of light. The use of LEDs means this kind of lighting can be energy-efficient and simple to control with smart, connected systems.

As well as letting us see, light evokes a physiological response in humans depending on its characteristics, such as colour spectrum, intensity and timing. Therefore, if we spend a lot of time indoors, it affects our circadian rhythm – the body’s master clock that helps determine our sleep pattern. HCL is supposed to aid our rhythm to improve health and wellbeing.

Dr Russell Foster, British professor of circadian neuroscience, is credited with > < discovering light-sensitive ganglion cells – which influence the body’s biological clock and are the basis of HCL – in the retina of the eye. The cells respond most sensitively to visible blue light, synchronising our bodies with the external cycle of day and night.

However, Foster says we’re not ready for HCL and it’s too early to implement it. Speaking at the Light & Building 2018 exhibition in Frankfurt, he said: “We can’t develop human-centric lighting until we know what impact light has upon human biology across the day and night cycle.”

According to Foster, there is no standard ‘recipe’ that manufacturers can use, as people are either ‘larks’ or ‘owls’ – lighting affects each group differently.

So what does the industry think? Mark King, product line manager of lighting at power management company Eaton, says: “General understanding around the impact that lighting has on the body – from its influence on the circadian rhythm to affecting moods and general wellbeing – has greatly improved. Yet the idea of human-centric lighting still has a way to go.”

Health and wellbeing is often linked to a good sleep and wake cycle; a disrupted rhythm impacts on how we function and our long-term health. Tiredness leads to stress, memory problems, lack of creativity, drug and stimulant use, obesity, lower immunity and even cancer.

Bianca van der Zande, scientist at Signify (formerly Philips Lighting), says the positive influence of light on our sleep-wake cycles has been studied in depth. “Production of melatonin, the hormone that helps to induce sleepiness and regulates our sleep-wake cycle, is impacted by natural and artificial light. In darkness, the body gets a signal to start production of melatonin; subsequently, if there is enough light, the body gets a signal to stop production of melatonin to become more alert.”

She adds that our natural body clock runs for between 15 and 30 minutes longer than our artificial 24-hour clocks. “Unless reset, this will make us want to go to bed later, causing us to be more dependent on our morning alarm. Correct quality light and timing can reset the half-hour lag and resynchronise our body clock with our artificial 24-hour clocks.” Morning light is very powerful in adjusting our sleep-wake cycle; artificial light that mimics bright daylight is said to be highly effective at regulating and synchronising, contributing to our overall health.

Human body clock

Image credit: E&T

Our mood can be influenced by light colour temperature – warm white is calming and neutral white is more stimulating. The colour rendering index Ra measures what colour display is the closest rendition to daylight. In offices, for instance, Ra greater or equal to 80 is needed.

Light distribution and direction influences visual performance and comfort. Osram Lighting Solutions says optimum HCL in an office requires a wide area with indirect lighting and high, vertical “illuminances” to create an “artificial sky”, with dynamic white colour temperatures and light control, and highly reflective surfaces.

For relaxation, the lighting must be warm with an elevated red component. Higher blue components/colour temperature influences our brain and body clock, increasing alertness, concentration and attention. Osram says the biological effect is strongest when light is emitted from a wide-area source and from above, as with sunlight.

Van der Zande claims there are already examples of the positive and tangible influence of HCL. “In Prague, we installed lighting in the Czech headquarters of energy company Innogy this year. It is tuned to support workers’ circadian sleep-wake cycles and stimulate energy levels at set times in the day.

“Employees enjoy a comfortable bright light, similar to natural daylight, to start their day and after lunch. This helps stimulate energy levels and enhance workplace comfort and vision.” She adds that the stimulus from the HCL fixtures is likened to a strong cup of coffee, which could be music to the ears of many workers who rely on mild stimulants to get through the day.

Yet Dawn Hollingsworth, principal of Darkhorse Lightworks, says the industry needs more funding for research. “There are roadblocks to implementation such as different priorities, costs and control systems that suppress demand,” she adds.

Eaton’s King explains that while many understand the idea on a granular level, i.e. mood versus lighting colour, one could argue that the idea has yet to be understood across the industry – and that lack of awareness is reflected in product development.

He adds that “in order to move forward, key concepts surrounding HCL must be understood by electrical contractors and installers. A deeper understanding of issues surrounding HCL on their part would provide added value for manufacturers, installers, and especially the end user,” such as workers in an office or factory, children in a school, residents in a care home or hospital, or you at home.

Hollingsworth says the lighting industry is great at talking to itself, but more needs to be done to educate the general public and those with the money to build projects.

“When people demand better lighting, the benefits will be evident, but until there is demand, HCL will continue to be a target for cost reductions and widespread adoption will be slow.”

King agrees that while it may be some time before we see HCL implemented on a regular basis, having a basic understanding of it will prepare contractors for when it’s time to move to this next level. “In the meantime, it’s important that installers choose the right luminaire to light every space in the best possible way,” he says. “This will not only maximise staff productivity, but it will deliver the best results overall.”

Alex Gifford, UK brand communications manager at Steelcase, says details like lighting, materiality, informal spaces and natural elements are powerful influences on behaviour and communicate company brand and culture. “It’s important to ensure the technology available is easy-to-use and accessible; frustration can build when there is discord between humans and technology.”

Signify’s Van der Zande adds: “Given that we as a species now spend much of our day indoors, as well as the advancements in our understanding of health, I expect the role of lighting in our physical and mental wellbeing to become increasingly commonplace in our daily lives.” *

Benefits of HCL



■ In the early morning hours, correct light can help students to wake up with less sleepiness.

■ Improved light environment can aid alertness and concentration.

■ At the correct time, higher-intensity lighting systems and colour temperature can improve learning quality and sleep.


For residents:

■ It can prevent mood swings and depression.

■ Stabilises human circadian rhythm.

Wellbeing improves due to better-quality rest and sleep-inducing drugs are reduced.

For staff:

■ Counteracts insomnia.

■ Improves employee wellbeing.

■ Under less pressure as residents experience correct activity and resting phases.


■ More intense and circadian light exposure can help employee alertness during the day and sleep at night.

■ Individual lighting control, which varies from person to person, may increase job satisfaction.


■ Intense lighting installations and tuneable white light may help production, fatigue and errors – effects are more apparent with repetitive tasks.

■ Shift workers may benefit from phase-shift lighting to ease into night work.

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