Human-Centric Lighting: Part 1 – featured in EE Publishers’ Vector Magazine


This article is based on the presentation I made at the IESSA Congress in Cape Town on 15 May 2017 and is featured in August 2017 Edition of EE Publishers’ Vector Magazine –


I was always aware of the fact that light played a significant role in our lives.  As I started to work with LED more and more which has been over the last 10 years of my 43 years of lighting experience, I realised even more that light had a considerable effect on us.

It was not until October 2010, when a South African lighting company sent an e-mail to retailers warning them not to use LED because it could result in their customers going blind.  Yes, it was as crazy as that! It was then that I really developed the insatiable hunger to learn more about the effect of artificial light and particularly LED light on humans!

That lighting company also attached the now well-known French ANSES report to their e-mail. ANSES tested and assessed nine different LED down lights and the results were contained in the report.  The results were extremely interesting after first having the document translated from French into English.  They found that three of the nine down lights were problematic and emitted large amounts of spurious royal blue light, note specifically royal blue which is the most intense short wavelength colour light.  It was found that children from birth until the age of sixteen do not develop the protective layer over the eye against that form of light until later and that adults over the age of 45 and who were already suffering from macula retinal disease, were more likely to suffer increasing negative effects which could hasten the onset of blindness or at least a degree of blindness from LEDs of such poor quality and with poor phosphor coating.  The report contained much interesting information most of which was positive about LEDs.

Current and Future State of Lighting Worldwide

Study the diagram in Fig 1 below.

Fig 1: Current and Future State of Lighting Worldwide

You will see that there are concurrent developments.  The so-called LEDification continues whilst the use of Intelligent Lighting Systems gathers momentum and much greater attention is also being focussed on Human-Centric Lighting.

Human Centric Lighting

I am sure that most of you have seen this stunning picture before.

It depicts the magic of natural light over a 24-hour period.

Before continuing, it is important that I first define Human-centric Lighting.  There are several variations on the theme! However, the following definition by LightingEurope is the best I have found to date:

“A type of lighting that can benefit the biological, emotional, health or well-being of people.  It can be achieved by dimming smart light sources such as LED to mimic the levels of sunlight throughout the day.”

Let’s check our understanding of Human-centric Lighting.

  • Without light, we cannot see.
  • Light or the absence of light, influences our vision and our perception of objects and our acuity irrespective of vision mode (photopic, mesopic or scotopic).
  • Light is the trigger of our emotional responses.
  • It connects us internally
  • It makes us feel good.
  • It makes us feel more effective
  • It is the trigger of hormone production.
  • It is responsible for growth
  • It provides us with comfort.
  • It makes us feel more secure.
  • It gives us energy.
  • It provides us with amusement.
  • It lights our task area.
  • It aids our health.
  • It is used in health care.
  • It is essential to help in care of the aged and dementia sufferers.
  • Used for water treatment (UV light)
  • Used for bacteria and germ control (UV Light)
  • Controls our Circadian Rhythms.
  • Light enables us to “Eat with our Eyes”.


The Human Body Clock or Circadian Rhythms

What are Circadian Rhythms?  Circadian Rhythms are physical, mental and behavioural changes that follow roughly a 24-hour cycle responding primarily to light and darkness in an organism’s environment.  They are found in most living things including animals, plants and tiny microbes and of course humans.  The study of circadian rhythms is called chronobiology.  They are not the same as our biological clocks but they are related.

The biological clocks that control circadian rhythms are groupings of interacting molecules throughout the body.  A so-called “master clock” in the brain co-ordinates all the body clocks so that they are in sync.

The “Master Clock” that controls circadian rhythms consists of a group of nerve cells in the brain each about the size of a grain of rice called the suprachiasmatic nucleus or SCN.  The SCN contains about 20,000 nerve cells and is in the hypothalamus, an area of the brain just above where the optic nerves from the eyes cross.

Circadian rhythms are produced by natural factors within the body, but they are also influenced by signals from the environment.  Light is the main cue influencing circadian rhythms, turning on or turning off genes that control an organism’s internal clocks.

Circadian rhythms can influence sleep/wake cycles, hormone release, body temperature, blood pressure and other important bodily functions.  They have been linked to various sleep disorders such as insomnia and sleep apnea.  Abnormal circadian rhythms are also associated with obesity, diabetes, depression, bipolar disorder and seasonal affective disorder (SAD).

Circadian rhythms are important in determining human sleep patterns.  The body’s master clock or SCN controls the production of melatonin, a hormone that makes you sleepy which is also an anti-oxidant, a cancer fighting hormone, anti-aging hormone and more.

Because the SCN are located just above the optic nerves, which relay information from the eyes to the brain, the SCN receives information about incoming light.  When there is less light, as at night, the SCN tells the brain to produce melatonin which also makes one drowsy.  The sudden introduction of light in the middle of the night has the effect of being a melatonin block.  The body will cease producing melatonin which can result in the body being inadequately protected and tiredness and fatigue will set in earlier during the day.  If the body has not produced sufficient melatonin, an increase in blood pressure can result which together with suppressed cortisol levels could lead to heart disease.

When melatonin production is interrupted repeatedly over a few nights, it results in sleep disorders and early waking.

In 2002, it was discovered that the ganglion cells in the retina produced melanopsin which controls hormone production.  It is fascinating to ponder on the wonder of vision and how it influences so many other biological functions.  Light reaches the eyes, light falls on the retina after passing the ganglion cell layer.  The signal is sent to the brain via the optic nerve and the SCN.  The pineal gland is triggered in low light to produce melatonin which leads to drowsiness.  At daybreak, we wake and the SCN triggers the production of other hormones which include:

  • Dopamine which we need for pleasure, alertness and muscle coordination.
  • Serotonin which controls our impulses and carbohydrate cravings.
  • Cortisol which we need for stress response and alertness.
  • And then at the end of the day, melatonin which leads to drowsiness, good sleep, lower body temperature and lower blood pressure which all contribute to our general rest and recovery or recharging.

It is interesting that studies have revealed that the much-loved early morning coffee or caffeine dose interferes with the production of cortisol which leads to caffeine dependence rather than the natural hormone.


Look at Fig 2 below.  It is interesting to note that we need high light intensity with high kelvin values to wake up and to regain our alertness at the start of the day and then especially after lunch, when we hit that afternoon lull, we need to be stimulated with higher light intensity and moderate kelvin value and then towards the end of the afternoon, lower light intensity and warmer lower kelvin value to prepare for home and the evening to induce sleep.

It is worth remembering that our predecessors and Fred and Wilma Flintstone did not depend on artificial light in the same way that modern society does.  They were also much healthier and did not suffer from many of the modern-day ailments, many of which have now been related to too much light, the incorrect type of light, modern lifestyles and of course poor diet including excessive junk food, sugar, high alcohol intake and smoking.

Understanding the Effects of Light on the Human Body Clock

The Fig 2 below has been used in many publications and presentation on this subject.  I make no apology for also using it because it so aptly graphically demonstrates the effects of light on the human body clock.  Take a moment to study the graphic.  It is really easy to follow.

Fig 2: The effects of Light on the Human Body Clock

What is generally understood by the lighting community about HCL?

The visual benefits to humans is well-known.  However, the slavish adherence to outdated standards and regulations where the focus is on illumination performance which occurs through an inadequate understanding and knowledge of the standards and regulations which gives rise to misinterpretation.  In addition, there is a lack of understanding or appreciation of the biological effects and the benefits of HCL which can result in better alertness, improved cognitive performance, good sleep/wake patterns, improved moods and less rage and improved impulse control.  Modern smart devices such as laptop computers, tablets and smart phones are not addressed in the outdated standards.

What are the Benefits of HCL?

Scientific studies and tests have shown the profound effects of HCL on 95% of all subjects who participated in the studies and tests which have been conducted in different parts of the world.  The general benefits include:

  • Groups were healthier.
  • Groups were happier.
  • Patients closer to windows or where HCL was in use, experienced faster healing.
  • Pupils and students had improved educational results.
  • Workforces were more productive.
  • HCL resulted in greater energy efficiency and lower operating costs of lighting.
  • More sustainable results.
  • Subjects slept sooner and better.
  • Subjects recovered faster.
  • Subjects woke easier and were more alert.


Remember that we also need healthy darkness.  The use of night lights has been proven to be a sleep disrupter.  Why do architects, engineers and interior designers still specify the use of night lights then?  There should be no device standby lights, no flashing or steady lights.  Smart devices such as tablets and smartphones should be placed on silent at least 1m away from anyone but it is preferable for them rather be turned off completely at night.  It is in fact better to leave them in another room.

Computers and smart devices including Kindles and LED TVs are sleep disrupters. They have a high blue light component and produce high intensity light.  These items should be turned off completely at least 1 hr and 30 mins before going to sleep.  Scientific tests on a wide cross-section of subjects has provided irrefutable proof!

Jet Lag and HCL

Jet lag occurs when travellers suffer from disrupted circadian rhythms. When you pass through different time zones, your body’s clock will be different from your wristwatch. For example, if you fly in an airplane from California to New York, you “lose” 3 hours of time. So, when you wake up at 7:00 a.m., your body still thinks it’s 4:00 a.m., making you feel groggy and disoriented. Your body’s clock will eventually reset itself, but this often takes a few days.

HCL is used to reduce the effects of Jet Lag.  When travelling East, the cabin lights are adjusted to provide more blue light early in the morning. Similarly, when travelling West, more blue light is provided late at night.  Most modern aircraft such as most newer Airbus and Boeing aircraft use LED cabin lights which can be adjusted to an HCL program.

Blue light features prominently to create alertness.  It is used in Swedish and Norwegian schools especially during the long dark winters in the mornings to improve alertness in the classrooms.

The colour Green has been found to be calming light. A more recent discovery has shown that green light can be used effectively to reduce the intensity of migraine headaches and in some cases it has successfully eliminated the migraine completely.

HCL and Elderly Dementia Sufferers

I am sure that everyone involved in lighting knows that as one ages, more light is needed to perform day to day tasks, in fact as much as 50% more light may be required in severe cases.  As dementia sets in, additional problems occur which include a narrowing of the field of vision, failing peripheral vision, tunnel vision and right-side vision.  Right-side vision, for example, can have the effect that the sufferer will only see the food which is on the right side of the plate.  The sufferer’s circadian rhythms and thus their body clock becomes out of synch and they produce melatonin in the morning and late afternoon rather than at night when they should sleep.  This results in sleep disruption which in turn results in sufferers to start wandering around their bedrooms at night which causes agitation and anxiety.

Therefore, HCL can play a very important role together with light therapy treatment which is given to sufferers in an attempt to reset their body clocks.   More blue-rich high intensity light is produced in the early morning until midday tapering off towards 16:00.  No blue-rich light to be produced after 16:00, only 3000K light to be produced, reducing in intensity until 18:00 which is normally bedtime in the care homes for the elderly.

Other HCL Considerations

HCL can be used effectively to create a relaxed atmosphere in medical rooms and dentist rooms.  Light lounges can be created to assist SAD sufferers.  Sunlight effect on the walls of rooms can be mimicked with Creative use of LED lights.  All the aforementioned uses of HCL can be further enhanced with the clever use of sound effects such as birds singing, traffic noise, etc.

Sleep Disruption

UK NHS Report of the Rise of Sleep Disruption in Children – March 2017.  The report states that there has been an 800% rise in the reported incidence of child sleep disruption with many children having only 2 hours of sleep per night.  The additional cost to the NHS is around £40bn per annum.  Some of the effects of aggravated sleep disruption are:

  • Rise in obesity
  • Increase in the number of children with Type 1 diabetes.
  • A dramatic rise in the number of vision defects detected.
  • Low concentration levels.
  • Increased number of cases of dyslexia.
  • Increased number of children diagnosed with autism.
  • Increased cases of anxiety and childhood depression which is said to last through adulthood.


The primary cause of the above problems is ascribed to smart devices.  Children are left at home with parents working until late.  Children spend hours unsupervised on smart devices to communicate with friends, play games and in many instances, they end up in trouble through being in contact with bad influences.  I have written an entire manual for my students on VDUs (Visual Display Units) and smart device screens within the working environment and the need for lighting designers to take great care when designing for such areas.  Our current standards were written for the days when computers were housed in special large rooms where tapes whirled and little panel lights flashed which was long before desktop computers even made their appearance.  It is really worrying to encounter great ignorance about the effect and dangers of VDU screens and the screens of smart devices on our vision.  In fact, those responsible for the writing of standards should make a detailed study of the light levels required for working with screens and smart devices as they are being used more and more in everyday situations at work, at home and at leisure.

NHS Adult Sleep Disruption Report

  • Most medical errors occur during the 3rd shift which is after midnight to 06:00.
  • Truck driver accident rates are alarmingly higher between midnight and 06:00.
  • Manufacturing errors and accidents occur during the 3rd
  • Excessive use of smart devices before sleep and during the night when waking, result in difficulty in going back to sleep and sleep disruption.
  • Sleep disruption can lead to cancers, heart disease, Type 2 diabetes, adult depression, sleep aponia, lower cognitive levels, inability to drive thinking processes and early onset of dementia.
  • The World Health Organisation (WHO) classify the 3rd shift as a Class III carcinogen.


The Latest British and Other EU Standards

They aim for:

  • Glare free lighting installations, lower illuminance levels, reduced uniformity whilst acknowledging that in certain cases higher illuminance levels may be required although such instances are in the minority.
  • Full colour spectrum lighting to emulate daylight and automated colour or hue change is a requirement for HCL.
  • High colour rendering index.
  • Lighting must be controllable by user/occupant/employ from smart devices including the ability to dim and change the hue, adjust air conditioning settings to allow the user to set their individual preferences.
  • To ensure that LED products that are used are flicker free and suitable to be used for Visible Light Communication or LiFi.



The importance of light, the intensity of light, the quality of light and the controllability of light has never been more important than at the present.  I have no doubt that it will become even more important as the development of lighting products and controls advance even further.

The sheer volume of this article does not allow for sufficient space to discuss the controls that are available for Human-centric Lighting to be effective.

Vector Magazine Link –



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