Is it time to re-assess Human Centric Lighting?

Do we understand enough about the neurological effects of light on brain functions in humans, especially when human centric lighting is being used in schools?

Let’s get some perspective right at the start; I like tunable-white lighting.

I think the psychological case for improving our health by warming up or cooling down our artificial lighting is well made. If nothing else, it makes my clients smile and that’s worth the price of admission alone. But there needs to be more to Human-Centric Lighting (HCL) than this.  

Some of my colleagues in the lighting design bubble deny the term completely. They say that good lighting design already contains the essential requirements for HCL, therefore there is no need for it has an individual concept. 

As the man wrote: this argument isn't worth a pair of fetid dingo's kidneys. (Translation: This is a poor argument.)

If we accept that there are three targets to be met in any HCL scheme, then this will help us to consider where the successes, and the failures, lie.

The visual dimension

I would argue that the entire visual aspect of HCL is missing. The visual dimension falls within the bubble of good lighting design that I mentioned above: but it is not a real factor in HCL design.

The emotional dimension

This is the aspect that keeps HCL going. Changing the colour of white light from warm to cool is fun. What’s not to like, and if we can key tonal changes with desired behavioural patterns (slowing school kids down, then waking them up is the common trope) then we can claim some kind of success for HCL. But this isn’t really what HCL was meant to be about.

The biological dimension

Have we got close to those bio-dynamic objectives that the HCL lobby have been chasing? Has any human-centric installation achieved a re-balancing of circadian rhythms, or created a better work-life balance, or acted to improve sleep patterns? The jury is still out on all three.

I don’t want to lose HCL. I just want us to look again at the meaning of the term.

We need to start from a different place if we’re to establish HCL as a meaningful metric for lighting design. I’d like us to go back to the island of Kos, for a moment, and listen to what Hippocrates said sitting under his tree: ‘First, do no harm.’

Before we start to make things better, we have to make sure we aren’t making things worse.

Here’s my personal list of things we need to ensure if we want to lay claim to human-centric lighting installations.

The quality of the illumination matches the environment for which it is intended.

I’m looking for lighting designs that suit the needs of the occupants of any given space. We spend many hours in our places of work and deserve a positive visual and non-visual environment.

Control of local and task illumination lies with the individual, not the organisation.

I would argue that the entire visual aspect of HCL is missing. The visual dimension falls within the bubble of good lighting design that I mentioned above: but it is not a real factor in HCL design.

We’re steadily moving from a blanket of light to localised illumination. That has been driven, in the main, by energy management requirements. The next stage is to reduce localised lighting levels and to introduce individual work-station task lighting.

Luminaires have appropriate glare and light output control.

This has always been part of any lighting code of practice but it has come to the fore in the age of the computer screen. For the most part, those glare demands no longer stand, but the drive to higher efficacy has brought with it commodified luminaires where light output trumps light quality. This has to stop.

There is no flicker below 100Hz from any light source.

Who’d have thought that flicker would be back on the design agenda? I’ve measured GU10 lamps and LED panels with a dominant flicker rate of 2Hz, putting them firmly into epilepsy territory. This is an outrage and needs to be brought under control. Flicker guarantees need to be provided for every LED source and luminaire. We mustn’t forget that flicker problems can be exacerbated by systems that include dimming in response to daylight harvesting, occupancy sensors, dynamic illuminance patterning – all in the name of good energy management.

A circadian rhythm ‘re-set facility’ is available within the installation.

At the heart of the human-centric debate is not the idea that lighting can make people work longer and better. At the root is sleep, which lies at the core of our healthfulness. One of the ways of helping sleep health is to ensure that our circadian rhythms are tuned to our environment. Whether it be a 1000 lux boost form the general illumination or a special ‘light shower’ facility, it should be a feature of any HCL installation.

There should be individual access to tunable colour temperatures.

Coming back to what I started with, even if it just makes us smile, that’s good enough reason to give people control over their local environment. Colour-tunable task lighting removes the ‘herd lighting’ aspect of recent HCL thinking. Yes, there’s a risk of ‘patchwork lighting’ with all those tonal choices on offer, but I’ll take the risk of upsetting the more anally retentive among us if it brings about a more congenial environment to live and work.

And that is it. Tick every box here and you’ve met the lighting requirements of the WELL Building Standard – and you’ve probably done it better and gone much further. But the flipside is that, unless you’ve ticked every box, you don’t have something that we should call a Human-Centric Lighting design.

Remember: First – Do No Harm.

Comments 2

As you know John, following our conversation at Clerkenwell recently, these are exactly my thoughts! A 'good' lighting design should always be 'Human Centric' - it just remains to decide how much 'tuneable white' is applied, what for and when. Let's start from first principles and use the technology when appropriate - not feel that we have to shoehorn in every piece of technology to our schemes simply because it is available.

Well said. There is a lot of other stuff to deal with here! Let's deal with glare, let's provide quality equipment and let's provide quality design. I'm in!

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