Circadian Lighting, Feature, Office

Official: How to implement human centric lighting

The publication of recommended practice has the potential to move human-centric lighting from the fringe to the mainstream and give the industry a powerful and profitable narrative as LED adoption passes its peak. Pic: Lux Review 2018

THE FIRST official recommended practice for implementing so-called human-centric lighting has been unveiled by a top industry scientist.

Scientist Mark Rea stunned a conference in Oslo by revealing a specific recipe that the industry could use to begin installing human-centric lighting. He described it as ‘putting a stake in the ground’. Pic: LR

Mark Rea, professor of architecture and cognitive sciences at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute in New York, told a conference in Oslo that the LRC’s specific recipe would allow the industry to begin installing human-centric lighting in workplaces, schools and other facilities.

The adoption of human-centric lighting – which, say proponents, sets occupants sleep-wake cycles and provides benefits such as better productivity, alertness and sleep – has been stalled by an absence of independent and authoritative guidance on its specific implementation.

Although human-centric lighting metrics have been cited in some standards, including the German DIN specification and the Well 2 wellbeing guidelines, the publication of the ‘recommended practice’ has the potential to move human-centric lighting from the fringe to the mainstream and give the industry a powerful and profitable narrative as LED adoption passes its peak.

In essence, Rea is specifying that occupants receive 254 lux of vertical illumination at the eye for at least two hours, ideally in the morning. It described the recommendation as a ‘stake in the ground’.

‘We believe we’re ready to go,’ said Rea. ‘We don’t know everything and the science is never complete…but science can clearly differentiate between big issues and small issues, and I think people forget that.

‘Sometimes they think the science is not complete, but we can tell the difference between an elephant and a mouse, I mean, we may not understand everything but at least we can tell the difference between that.

‘So a good recommended practice must include the science and its uncertainties, and our recommended practice has bent over backwards to say what we know.’

The 254 lux is based on a criterion that it will suppress the sleep hormone melatonin by 30 per cent. Lux is used, says Rea, because that’s a measure that the industry understands.

The specific spectrum of the light is not specified because the recommendation is not a replacement of circadian-effective light index or anything else. ‘This is just what you need for biological effectiveness. The SCN (suprachiasmatic nucleus region of the brain) doesn’t care about colour rendering, it just doesn’t care. Your visual system cares a lot but the circadian system doesn’t’.

‘Now, do you really think three significant figures can be justified in terms of the science?  No. But you have to engineer something. So that’s our target. 250 lux of daylight for at least two hours, and ideally we believe in the morning. That’s what we’re going to declare, put a stake in the ground, that’s what we’re going to engineer.’

Rea emphasised that it was up to engineers and lighting professionals to design the physical lighting that would deliver the recommended practice in the real world.

‘The key question for a recommended practice is: how am I going to engineer this stuff?  I’ve got to take these qualitative bright lights during the day, dim lights during the day, but what do you mean by bright and what do you mean by dim, how do I know that, how do I engineer it in a way that I’m going to give reliable differences.

‘You want to go to a customer, pick a big one, Volvo, say…and you say, “I’m going to give you a lighting system, and if you follow these engineering principles we’re going to give a sample of 20 of your workers and I’m telling you they’re going to sleep better than they did before.” That’s sticking your neck out, isn’t it?  But isn’t that our obligation?  Isn’t it, fundamentally?

The metric can be adjusted for various luminaire formats and colour temperatures, where 1 is the base of 254 vertical photopic lux measured at the eye.

‘This isn’t everything for a lighting designer. [The lighting installation] still has got to not cause glare; you’ve still got to be able to see; it’s still got to be cost effective. This is one design element; this is not everything you ever need to know about lighting design.’

Rea told the conference – hosted by leading human-centric lighting manufacturer Glamox Lighting – that the recommendation was not a permanent solution. ‘This is something that is our best guess right now and it will evolve.

‘We’re not forcing anybody to do anything. We’re just saying if I want to do [human-centric lighting], this is what I need.

‘And there are many ways to get there, so we’re not trying to tell you that you have to do it from the ceiling or from a table top or anything else, or even go outside for two hours, which apparently works pretty well.

‘If that’s the work environment that works best for your client, do it. Don’t force them into some solution because you happen to have it in the warehouse and you want to sell it. I think that’s a bad idea.

‘But there are no guarantees here. You don’t have to do this if you don’t want to. If you do, this is the number.’

The recommended will be shared for public review in December with an anticipated official publication in the spring of 2019.


  • Human-centric lighting is the key theme of the Lighting for Workplace and Wellbeing conference track at LuxLive 2018. Speakers include human-centric lighting experts Dr Octavio Perez of Mount Sinai Hospital and Luke Price of Public Health England. See the full programme HERE. LuxLive 2018 takes place on Wednesday 14 November and Thursday 15 November 2018. To register for free, click HERE.