Human-centric lighting represents a new way of using light in our lives, but it is understandable that there is some skepticism over its use and its effectiveness. Do we know enough about the technology, for example, to be using it in schools? Is there enough evidence to say that human centric lighting improves productivity at work?  Can HCL help to maintain a smooth circadian rhythm at home?

In a 'Clash of the Lighting Titans' Lux's applications editor John Bullock (a HCL cheerleader) and our technology editor Alan Tulla (a sympathetic skeptic) sit down to compare and contrast their human centric lighting opinions.

(JB) 'Human-centric lighting, unlike previous lighting advancements, puts life at its very heart.

We now know that ‘white light’ is more than a matter of colour temperature and colour rendering. We also know that the natural light spectrum generates subtle signals telling the body whether it should be awake or asleep.

Connecting the technology and the science means that we are able to work more closely with the natural light-dark rhythm of the world.'


(AT) 'Having evolved without artificial light, it would be strange if light did not have an effect on us both physically and psychologically. However, Circadian rhythms are nothing new, they have been with us for millennia.

I strongly believe in the principles behind Human Centric Lighting. Bright sunlight can give you a real boost. Equally, Seasonally Affective Disorder, SAD, is a well-established medical condition that can be treated with high levels of light for long periods of time.

Where I disagree is in what we should do next. More importantly, do we even have enough knowledge to know what to do next?'


(JB) 'Teachers have long complained that it is difficult to maintain students’ attention throughout the day and it has been proven that students suffer from attention-deficit first thing in the morning and post-lunch.

A carefully-tuned system is overcoming these problems by introducing light into the classroom with a higher blue content in the part of the spectrum that subdues sleepiness.

The same system is used at other times of the day when young children may be over-active. At such times, the lighting can be adjusted to reduce the amount of blue light entering the classroom in order to settle the mood of the classroom.'

(AT) 'There has been a lot of experimentation in schools but the results have been quite different. For example, when the children first arrived in the morning, one school used high levels of illuminance and high CCT to boost the students’ concentration ready for the lessons. Conversely, another school did the exact opposite because the children were excited when they first arrived and needed to be calmed down for their first lesson.

A manufacturer who promotes HCL told me that these examples prove that it works. The school just has to decide what effect they want and the lighting can be adjusted accordingly.
The question is, of course, what is a school actually meant to do?  Somebody, somewhere, has to set the controls either to dim down or to increase the illumination and CCT.'