Human-Centric Lighting: Part 2 – featured in EE Publishers’ Vector Magazine

This article is featured in the September 2017 Edition of EE Publishers’ Vector Magazine –


On reflection, there were many aspects of human-centric lighting that I did not cover in my first article.  In this sequel, I will endeavour to ensure that those omissions are covered.

Opening comments

Recently, whilst in Madrid, Spain, we visited the Museo Archeologico Nazionale (National Museum of Archaeology).  Whilst delving into the distant past from the Iron Age through to the Renaissance, other than looking upwards to see how the museum had been illuminated in the different areas, I also became acutely aware of the fact that from the earliest of time, homo sapiens depended on light and feared the dark.  Even after death, a small form of light would be left with the departed to ensure that they did not descend into darkness.  I discovered that it was around 1.7 million years ago when our ancestor Homo “Erectus”, during the Early Stone Age (or Lower Paleolithic) was found to have started to use fire as a source of warmth, protection, a method for cooking of food and it allowed the expansion of activity into the dark and often colder hours of the night. With the development of “fire control” it allowed the early “Stone” Age people to fashion flints and other utensils such as stone axes and spears.

Over time, various other light sources evolved from hollow rocks or shells filled with dried moss and animal fat, to oil lamps and early candles around 3000BC.

Early light sources did not evolve further throughout the Renaissance period.

It was only in 1780 that the “modern” oil lamp came into use. Since then, light sources have developed at what we could describe as an “unrelenting pace”.  LED development appears to have no end.  It is continuous, exciting and fast.

If we perhaps would like to apportion blame to someone for the “disruptor” called artificial light, it could be William Murdoch who in 1792 discovered how to produce and store coal gas.  He was then able to light his house in Redruth, Cornwall where he was a bit of a “party animal” and used to entertain prolifically.  He went on to illuminate first the outside of the Manchester police commissioner’s office and later the inside as well and then the outside of the famous foundry in Birmingham belonging to James Watt and Matthew Boulton.


Darkness, our primordial dread, lost its dominion.  Soon the industrial revolution gained momentum, taking full advantage of this “new light” which extended the hours of daylight!

The Present

As the years passed from one century to the next, artificial light became a greater and ever greater part of human daily life and routine.  There was a constant search for brighter and more efficient, lower cost light sources right up to the present day.  Similarly, the advent of computers and the evolution of smart devices, have brought with them some major problems for the users within society.

It is only since Professor Russell Foster CBE, Head of the Nuffield Laboratory of Ophthalmology and the Sleep and Circadian Neuroscience Institute, discovered that there were non-core photoreceptors in the human eye in 1995 for which he was awarded the Honma Prize (Japan) and various other awards.  He also found that the brain substance Adenosine prompted sleep and that some people were more sensitive to this substance than others which resulted in them falling asleep earlier and sleeping for longer.

Human-centric Lighting

This was substantially discussed in my first article.  I would now like to play devil’s advocate and pose some interesting thoughts that many others have also posed.

Is human-centric lighting baloney or witchcraft?  Is it a buzz word or a term that is in vogue?

Why does my wife fall asleep in front of the TV?  In fact, why do I get sleepy when watching TV in bed and simply fall asleep, even with the TV still on only to discover that when I wake at my normal time of waking?  How are we able to sleep soundly even if we have fallen asleep with the lights on?  How do people take 40 winks in broad daylight?  Why is there now proof that workers who are able to control the light level in their personal space, prefer to work under a light level of around 150 lux?

These questions which have been asked by many and which I have asked myself from personal experience, indicate to me that in the light of the overwhelming scientific proof that human-centric lighting is valid, the questions raised reveal that there will always be those exceptional instances.  The cause of such instances can be so varied such as excessive tiredness through over work without adequate sleep, to international travel, high stress levels and surely many other reasons as well.

I have no doubt that human-centric lighting will play a very significant role in all future new build lighting designs.  We cannot avoid it or simply hope that if we turn our backs on it, it will go away.

How do we implement HCL?

I am sure that the readers understand that we need some form of control system to regulate the type of light needed at different times of the circadian cycle.

There are various control systems, each of which have their own and sometimes limiting characteristics.  Here are a few of the available control systems:

  • DMX512.  This system, the Digital Multiplex, is a standard for digital communication most commonly used for stage lighting and effects.  Over more recent years, it is used for non-theatrical interior and architectural lighting.
  • DALI.  DALI stands for Digital Addressable Lighting Interface and is a protocol set out in the technical standard IEC 62386. Controllable lighting systems are the key for energy saving in building lighting installations with the additional benefit of increased comfort and safety. DALI was developed as an        international industry standard for intelligent and easy management of lighting equipment. The standard incorporates several parts that provide control and monitoring functionality for ballasts, emergency gear and LED gear, and now also for lighting controls.
  • KNX.  This is a standardised OSI-based system of network communications protocol for building automation and management.  It is administered by the KNX Association.  It is a system which enables the various parts of a building system to be controlled in a single control system.  This includes all lighting, heating/ventilation and air-conditioning control, shutter and blind control (excellent for use when daylighting is in use), alarm monitoring, energy, electricity, water and gas metering, audio and video distribution which can have access enabled via a LAN, analog or mobile phone network to have a central or distributed control of the system via PC’s, touch screens and smartphones.
  • LONWORKS.  It is a local operating network platform created to address the needs of control applications.  It uses twisted pairs, powerlines and fibre optics and is used for the automation of various functions such as lighting and H Vac.  Its uses extend to machine control, intelligent electricity metering, street lighting, subway train control, building lighting, stadium lighting and speaker control, security systems, fire detection and suppression and many more applications.

It should now be clear that we have a good choice of top quality control systems which makes it possible to select the control system to suit the sized application for human-centric lighting control.

Other aspects relating to the use of LED lighting with control systems that we have to address is the issue of spectral variations.   Millions of years of evolution have shaped us to sleep in total darkness and to be awake under natural daylight.  Generally, we are at our best level of performance at the peak of day or midday.  So, we will now look at the spectral variations of light.

Whilst this diagram is valid for the northern hemisphere, it illustrates how the hue of daylight changes over the course of a day.  The latitude and time of the year also influences the colour temperature values for a particular hour.

I am sure that you will agree that it is artificial light which must adapt to our basic need for daylight and not the other way around.

To do this, lighting product manufacturers now produce products to emulate daylight offering a single light unit that can be adjusted from 2700K (warm white) all the way through to 6500K cool white.

The theory of human-centric lighting is that we need high intensity cool white light early in the morning to wake us up and increase our levels of alertness and again in the early afternoon which is usually after a midday lunch irrespective of how substantial it may be or not and then from mid- afternoon warmer light in preparation for going home and eventually to bed for the night.

My question is – how does this relate again to various overseas installations where the employees have personal control of the light levels in their work space?  Surveys that have been taken have shown that the preferred level of light to work is 150 lux in spaces where the lighting design was 300 lux and where the system even enables the employee to increase the light level to 500 lux.  The system where employees can control both the light levels and air conditioning temperatures is referred to as democratised control.

We cannot overlook the findings of the International Ophthalmic Conference that over-illumination in the workplace is between 2 and 5 times the level of light actually required for the activity.   You may ask: “What about task areas”.  To answer that question, it is necessary to first understand the hierarchy of working areas.  The activity is the highest level, followed by the task, followed by actions and finally operations.   In South Africa, we are obsessed with the word “task” and furthermore lump an entire space into a single task.  This practise is directly responsible for over-illumination in the workplace.  It is also the primary reason for excessive uniformity which is the single most negative form of lighting and which leads to eye fatigue.

Considering the theory of HCL, democratised control and the findings of experts in the visual field, it is my opinion that the colour of the light at particular times of day is far more important that the intensity of the light.  It is vital to provide comfortable lighting levels so that employees can execute their activities whatever level they may be within the hierarchy of activities to promote well-being and good health in the workplace.  That is what the aim of good lighting is in the Occupational Health and Safety Regulations: Environmental Regulations in the Workplace surely?  Even if it is so incredibly out of date and step with modern lighting technologies.


The members of the committee revising the lighting standards and the Occupational Health and Safety regulations pertaining to lighting should be up-to-date with the latest technologies and practices in the rest of the world and they should a thorough understanding of human-centric lighting and the neuroscience which underlies it.  I unfortunately am doubtful whether these modern aspects of lighting practice have been considered to date.  I appreciate each day that lighting is far more complex than any of us originally thought when we entered the profession as illumination engineers and lighting designers.  The important message that I would like to leave the readers with today is, never stop reading and studying.  Just when one thinks that we think that we know it all, there are changes – new technologies, new studies and research, new discoveries and still new information that refutes that which we had once learned.

I hope that the articles have stimulated your interest and that you will be encouraged to read and study.  I am by no means an expert in this vast field, but I do know more than many others out there and yet I am still learning.

Vector Magazine Link –



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