ILP Presentation - The Circadian System and Lighting

The Circadian System

and Lighting

Copyright Institution of Lighting Professionals

1. What is the Circadian System – and how is it affected by light?

Circadian Rhythms

The circadian system has been observed for many years in humans and other organisms. Circadian rhythms describe the body’s physical, physiological and psychological changes over a 24-hour period (Latin: ‘circa’ = around, ‘diem’ = day)

Embedded within our genes are the instructions for a biological ‘clock’ that marks the passage of 24 hours (approx.)

However, until recently we didn’t know what governed – or ‘entrained’ these rhythms. We now understand much more about how our circadian rhythms are controlled – and the key is light, particularly daylight

The ‘Third Eye’

We have learnt in the last 20 years or so that the effects of light go well beyond visual function and comfort

There is a non-visual pathway from the eyes to the brain, totally separate from vision

Information about light levels is sent to the suprachiasmatic nucleus (SCN) in the hypothalamus – a tiny receptor with about

50,000 neurones.

The SCN is like a master pace-maker, co-ordinating all the cellular clocks in the body via the endocrine system, which produces various hormones across a 24-hour period

Location of the ‘third eye’ or the Suprachiasmatic Nucleus (SCN) in the brain which responds to light levels and controls the body’s hormone system – and ultimately the circadian system

The ‘Third Eye’

In particular, the process stimulates the pineal gland to produce – or reduce– the level of melatonin (‘the sleep hormone’) in the body, depending on the level of light

Low light will stimulate melatonin, which makes us sleep; and bright light will suppress melatonin production.

A robust 24-hour pattern of light-dark (preferably provided by daytime exposure to strong natural light) is vital to maintaining our bodily health and well-being – and in particular our regular patterns of sleep and alertness

The Chilean miners trapped for two months underground, without daylight, would have experienced the total disruption of their circadian rhythms in an extreme way

Light and our Hormones

However, it is not just wake-sleep patterns which are governed by this light-regulated ‘body clock’

Our entire endocrine system,producing essential hormones that control our 24-hour bodily functions (sleep, hunger,

mood, blood pressure, alertness, tiredness etc.) are governed by patterns of light/dark, as interpreted by the ECN

Without daily exposure tobright light at dawn, circadian

rhythms become ‘free-running’ and body functions are ‘de-synchronised’, leading to declines in alertness, physical performance and poor health.

The Endocrine System

Circadian Rhythms and the Body

Correspondence between day-night cycle and some physiological functions

The Circadian System in Action

Here is a graph showinga 48-hour cycle of the body’s circadian system, and the production of melatonin (sleep hormone), cortisol (which maintains alertness during the day) and growth hormones, vital for cell production and replacement. Cell replacement and bodily growth occur almost entirely during the hours of sleep – so one can appreciate the serious effects of poor sleep

2. The Negative Effects of Circadian Disruption

Cancer and Night Shift Working

One of the best-known epidemiological relationships between the disruption of normal sleep and health has been discovered with nurses working on night shifts Firstly in Israel, then confirmed in other countries, it was found that nurses who regularly worked night shifts had a higher incidence of breast cancer than nurses working day shifts One likely cause is that night-shift nurses lack exposure to bright daylight – this disrupts their circadian system, and in particular the production of growth hormones Cancers are caused by malfunctioning cells – so if the

pattern of normal cell replacement is disrupted, then those malignant cells could have more opportunity to develop

The Importance of Blue Light

However, not all light is equally effective in governing the ‘body clock’ – or disrupting it

Research has shown that it is short wavelength (around 484nm) blue light in the spectrum which is most effective in the circadian process

Daylight has a large blue component – as do ‘cold’ fluorescents, metal halide lamps and many LEDs

These sources are most effective in setting our body clocks – ‘warm’ lamps, such as HPS, LPS and tungsten halogen are least effective

Biological and Physiological Effects of Light

Of course, the wrong type of light at the wrong time can disrupt these rhythms – e.g. large doses of blue light in the early evening can keep you awake.

Just as the circadian system is maintained by a regular ‘light-dark’ cycle, circadian systems can also be disrupted by too little light during the day – or bright light at the wrong time at night

This can cause the disruption of sleep patterns – and is often associated with other health problems. There is evidence that long-term sleep problems and circadian disruption can contribute to chronic maladies such as diabetes, obesity and hypertension

Circadian disruption also seems to be related to increased malfunctioning of the immune system – even one night’s lost sleep can reduce the activity of white ‘killer cells’ in the blood by up to 28%

The Effects of Disrupted Circadian Rhythms/ Shortened Sleep

The known effects of chronic circadian disruption:

Drowsiness and unintended sleepMood shifts and irritabilityAnxiety and depressionWeight gainDecreased socialisation skills, communication skills and sense of humourDecreased motor and cognitive performancePoor concentration and memoryIncreased risk-takingDecreased creativity and productivityReduced immunity to disease and viral infectionReduced ability to multi-taskIncreased risk of substance abuse

The Arrival of Electric Light

Human beings evolved over millions of years in Africa, where day and night length was fairly equal – and where blue sky in the morning ‘naturally’ signalled waking and red sky at night meant sleep

In agricultural societies, most work was done during daylight hours – with domestic/ artisanal work carried out by light from (expensive) candles or oil lamps

This adherence to the solar 24-hour light- dark cycle was severely disrupted by the arrival of electric light in the 19th century, which coincided with the requirements of industrial society to extend the working day

Lengthened hours of work and leisure created the immediate potential for disruption of circadian rhythms and sleep patterns

Common Examples of Disruption to Circadian Systems

1. ‘Jet Lag’

Long haul air travel is one of the best-known examples of how our circadian rhythms can be completely disrupted – rapid transfer to another time zone means your body is completely out-of-synch with the day-night cycle around you

The rhythms that dictate times for eating, sleeping, hormone regulation and body temperature variations no longer correspond to the environment nor to each other in some cases

The sufferer can feel groggy, tired, listless, disoriented and have poor concentration

It usually takes the body one full day to adjust to each one-hour time zone crossed, although susceptibility varies from person to person

Causes of Circadian Disruption

2. Night shift work

We have already touched on the more severe effects of night shift workMore than 20% of the UK population works at some time outside the 7.00-19.00 dayThe effects are similar to jet lag… except that shift workers almost never shift their circadian rhythms in response to working at night, because they are always subjected to low artificial light levelsThe long-term results of extended periods of poor sleep are a higher incidence of cardio- vascular mortality, peptic ulcers and certain cancers, plus a propensity to accidents, chronic fatigue and depression


3. Office Work in WinterHowever, workers don’t have to work night shifts to be affected by circadian disruption. In the winter months, many workers go to work in the dark, come home in the dark and work all day in artificially lit environments like this…

Without experiencing bright daylight, their body clocks will not be re-set on a daily basis and they could experience poor sleep, tiredness, lack of performance and depression.

In some people this manifests itself as ‘SAD syndrome’


4. Exposure to bright light in the evening

There is now increasing concern that people are exposing themselves to levels of light with a high blue content shortly before bedtime – via laptops, tablets, TVs, LED bedside lights and so on

This may be sufficient to suppress melatonin levels in the blood, making it harder to sleep

There is also evidence of a link between night-time lighting in bedrooms and obesity – currently under study


5. Modern Street Lighting?There is even a chance that modern street lighting could contribute to the problem

Firstly, we are seeing the rapid replacement of old- style sodium based lighting (bottom) with both metal halide and LED light source (right)… which have more blue in their spectra

It used to be thought that to affect the circadian system, light levels had to be in the 800-1000 lux range

However, recent research by the LRC in the USA has shown that one hour’s exposure to 100 lux of light from a ‘cold’ (6900K) street light can suppress melatonin levels in subjects by up to 15%

What might happen if such lights inadvertently shone into poorly shaded bedroom windows all night?

Older People: Circadian Victims

Disruption and impairment of the circadian system is increasingly common in older people for a number of reasons:

Whether at home and in care institutions, older people tend to get less exposure to daylight and sunlight than any other group

At the same time, they experience neural degeneration in the retina, so less light reaches the back of the eyes

Also thickening of the lens of the eye, plus yellowing of the cornea, filters out blue wavelengths (right)

So less light in general, and less blue light in particular, is available to trigger the circadian system.

Increased lens density with age = less blue light

Older People: Circadian Victims

The situation is exacerbated by the poor design of care homes for the elderly

Older people at home or in care institutions often lack high levels of light, particularly natural daylight

Most facilities have constant, relatively low levels of artificial lighting – and constant lighting impairs sleep ability

In a recent survey of 11 new build- ings built for elderly occupants, nine lounges were lit to only half the recommended minimum – and 30% of lounges, 50% of dining rooms and all the activity rooms fell short of the minimum daylight level for new building interiors in the BS Code The constant demand for energy con- servation is making the problem worse

Not too bright – a typical interior of an old people’s home

School Hours and Disruption in Children

Curiously too, we have discovered that children are inadvertently subject to circadian disruption in their everyday lives

It appears that not all age groups have the same diurnal rhythms – sleep timing changes markedly as we age

By the time of puberty, ‘natural’ bed times and waking times drift to later and later hours – yes, young people do need to sleep longer in the mornings!

This tendency to get up later increases up until about the age of 20 – and then it goes into reverse, so by the time we are about 60 waking times are similar to a 10-year old

School Hours and Disruption in Children

Teenagers made to get up early for school show both delayed sleep and high levels of sleep deprivation, which makes for diminished performance and poor concentration

These real biological effects have been largely ignored in terms of the structure of school timetables

In limited experiments, later school start/finish times have produced improved alertness and mental abilities in the morning… but interestingly, the performance of their older teachers suffered!

3. The Positive Effects of Circadian Lighting

Positive Effects of Circadian Lighting

However, as evidenced by the school example, lighting can also be used in a number of positive ways to enhance people’s alertness and wakefulness during the day and improve their sleep patterns at night

A number of sleep disorders may respond to light therapy, including:

Advanced sleep phase syndrome and delayed sleep phase syndrome (i.e. where people go to sleep very early or very late)

Non-24 hour sleep-wake cycle, , where fall asleep at different times of the day each day

Jet lag

Shift work Age-related fragmented sleep in healthy and demented individuals

Some of these areas are detailed later


A number of studies, experiments/trials and actual real-life applications have confirmed this – and we will conclude by summarising some of these examples

However, we need to tread carefully… circadian science is relatively new and there are still lots of unknowns

Real-life circadian lighting design applications, in offices, homes, schools or institutions for the elderly, often lie beyond the remit of mere lighting design schemes – and slip over into the realm of the therapeutic, in actually changing people’s behaviour or physiological state

Remember…

Lighting designers are not doctors… or trained therapists


There are two classes of lighting intervention which could be called ‘circadian’ applications:

1.The manipulation of workplace, school and other interior lighting during the day (and with shift workers at night) to facilitate ‘alertness’ and working efficiency. This usually done through greater brightness or intensity and sometimes through changes in colour temperature.

2.The use of (usually) blue-enriched interior lighting, usually applied early in the evening, to ‘re-set’ the body clock and ensure improved sleep

…but we must never forget the crucial role of natural daylight…

The Morning Walk

Daylight is the most important positive factor in circadian health and alertness.

According to research by Professor Russell Foster of Oxford University, a 30-minute walk in the morning is better than any amount of artificial light

Taking a 30-minute walk in the morning sunshine can help people who struggle to sleep because it helps regulate the body clock. A sunny day is equivalent to 100,000 lux while indoor lighting only provides around 300 lux. The average person needs exposure to 1,000 lux to enjoy the maximum benefits.

To quote Professor Foster, ‘Light is not just important to the visual system, it helps regulate the brightness detectors which affect our bodies. If you do not get any other light during the day, make sure you get out and experience morning light, which helps set the body clock. Outside light is bright enough to do the job, even on a dim day.’

Natural Light in the Workplace

Another recent study found that workers who had a window in their office had a much better sense of health.

Exposure to natural light during the working week tended to inspire people to exercise more.

Workers with a window were also better rested: those with windows got 46 more minutes of sleep a night on average, and the ones without windows had more sleep disturbance.

Some studies show that people feel better, are more alert and work best at an ambient light level of about 100 cd/m2. Through a 2009 field study, undertaken in a middle school in London, an ambient light level of around 100 cd/m2 – provided by artificial and natural lighting -- improved student performance, alertness and well-being.

Natural Light in the Workplace

It has long been known that views through windows and natural lighting are preferred by office workers.

One study has shown that sitting next to the office window on a sunny day can help double an individual's alertness compared to those stuck in the middle of a room under artificial lights.

Less than 5% of daylight filters into the average building, and energy-efficient light bulbs are largely ineffective, due to their lack of intensity and poor spectral composition.

But on a bright day, those next to a window will

benefit from the sunlight, while their unfortunate colleagues will be left feeling less energised.

The Important Factors

There are a number of factors that need to be considered in all artificial lighting applications for circadian effect:

The LIGHT INTENSITY The DURATION of the lighting applicationThe SPECTRAL COMPOSITION of the lighting (in particular, whether it has a high blue content).In general, the more intense, the longer duration and the more ‘blue’, the more the light will enhance alertness (and affect circadian clock timing)

The Important Factors

Most importantly, there is the TIMING of the lighting, in relation to a person’s own biological clock time.

The closer the light administration is to a person’s melatonin peak (which is also the persons’ core body temperature minimum) the more effect it will have in shifting the timing of the circadian clock.

This melatonin peak is around 4.00am in normal non-shift workers.

If you receive light BEFORE your melatonin-peak/core body temperature minimum, this will delay clock timing, thus delaying the onset of sleep

If you receive light AFTER your melatonin peak/core body temperature minimum this will advance the clock timing, thus you will wake up earlier (the can happen using ‘wake up’ lights; or with daylight coming through windows in the morning

The Melatonin Peak

The circadian clock and melatonin production in the body – with a 4.00am peak

Lighting for Workplace Alertness

We have already discussed the positive effects of better daylighting on office workers

There is now considerable evidence that the application of brighter levels of blue-saturated artificial light in workplaces during the day can improve alertness and work efficiency

‘Variable’ lighting systems are now being installed in offices in which both the light intensity and the colour temperature can be adjusted across the day – but there is as yet no firm consensus about the best combination and timing, for producing the most favourable results

However, because these variations take place many hours away from melatonin-peak/core body temperature minimum (usually 4.00am) such interventions are unlikely to advance or retard the circadian clock

Lighting for Workplace Alertness

In one trial, blue-enriched white light at 17,000K improved subjective measures of alertness, positive mood, performance, evening fatigue, concentration and eye discomfort

Daytime sleepiness was reduced and the quality of subjective nocturnal sleep was also improved under blue-enriched white light.

In another study, exposure to light at 6500K induced greater melatonin suppression than ‘warmer’ lighting with less blue content, together with enhanced subjective alertness, well-being and visual comfort.

Light at 6500K also led to significantly faster reaction times in tasks associated with sustained attention

This cognitive improvement was strongly related to lower salivary melatonin levels, particularly for the light condition at 6500K

‘Jet Lag’

‘Jet lag’ due to long distance air travel is one of the most common forms of circadian disruption – and while ‘trivial’ for most people, it can have much more serious implications for critical workers, such as air crew, industrial process workers, oil field workers and so on

Again, the ingestion of melatonin (not available in the UK) can help to re-set body clocks

The careful application of daylight can also help enormously – but the regimes vary depending on the direction of flight:

EASTWARD flights: the best regime is bright light therapy (natural or artificial) in the morning after your normal (home) wake time and dim light prior to bedtime

WESTWARD flights: the best regime is bright light therapy in the evening before normal bedtime (home) and dim lighting after wake time

Lighting for Shift Work

Given that night-shift working is well known disruptor of circadian systems – and in the long-term can lead to serious health problems – improved lighting to alleviate the problem is a major priority

Even in the short term it can lead to:

Wandering and disconnected thoughts Headaches or stomach aches Drowsiness during shift and inability to sleep after shift Inattention to minor but potentially important details Degraded mental abilities (including memory, decision-making, and perception) Increased distractibility and irritability

The last hours of any shift are the most likely time for industrial accidents… and night-shift workers are 4 to 5 times more likely to have car accidents

Owl or Lark?

Most people have a genetic pre-disposition to be either an ‘owl’ or a ‘lark’ – i.e. they go to bed late/wake late or go to bed early and wake early in the morning

The physiology of ‘owls’ means they are probably far more suited to night-shift work – and more likely to adjust successfully to sleeping during the day

Perhaps this ought to be taken into account during recruitment


Interventions with shift-workers usually give bright light in the early part of the night shift (to increase alertness) and then stop it – or apply much ‘warmer’ light (to avoid it effecting circadian timing too much).

This can be administered by the general ambient lighting system – or in smaller companies individual desk-top light boxes can be purchased in a variety of makes and sizes. The box houses light tubes or LEDs that produce extremely bright light.

One model, the Litebook, is seen here


Other strategies recommended by some experts are the use of yellow-tinted light in night-shift workplaces

Shift-workers are also advised to return home in the morning and avoid as much of this morning light as possible as this will delay the time of their daytime sleep. Some experts even recommend wearing yellow glasses or goggles to cut out the blue in daylight.

Bedrooms should be kept very dark during daytime sleep with daylight excluded

The use of artificial melatonin has also been shown to help shift workers sleep during the day. Although widely available in the USA, melatonin is only available online in the UK.

Lighting for Older People

We have already seen that older people – in all residential contexts – are severely disadvantaged, when it comes to receiving sufficient light to maintain their circadian health

Disruption and impairment of the circadian system is increasingly common in older people.

As a result, 40-70% of people over 65 suffer from chronic sleep disturbance – and Alzheimer’s sufferers are particularly affected

Therefore the provision of artificial lighting to compensate for this is crucial

Lighting for Older People

Light with a high blue spectral content is most effective in therapeutic terms

Studies have shown that the use of blue-saturated light with care home residents in the afternoon increases sleep at night – and day-time alertness

In addition to sleep disorders, depression can be exacerbated by disrupted circadian rhythms (as it can be with younger people who suffer

from SAD syndrome) When older people are exposed to high circadian light levels during the day, and dim levels at night, sleep duration and efficiency are improved – and the incidence of depression reduced

Lighting and Dementia

The disruption to the body's circadian rhythm, governing sleep and wakefulness, can be one of the most difficult of dementia symptoms for carers to cope with.

People with the illness can often be asleep during the day, but fully awake for periods during the night.

Although the illness itself is incurable, certain types of circadian therapy seem to have a significantly positive effect on Alzheimer’s patients.

Dutch trials with dementia patients using blue light (with and without melatonin) improved night-time sleep patterns, slowed cognitive deterioration and reduced depression, agitation and aggressiveness

The study concluded that these measures could slow deterioration by 5% - which a UK specialist said meant patients living in their own homes for months longer.

Lighting and Dementia

Research in the USA showed that exposure to bright morning light (2,500 lux for two hours) reduced agitation among elderly patients with dementia patients were significantly more agitated on non-treatment days.

In another study, when daytime illumination levels were increased in different living spaces of a dementia unit, the stability of the rest-activity rhythm increased in patients with intact vision (but not in visually impaired patients)

Improved Lighting and Recovery Times

Improved lighting, particularly more daylighting, has been shown to have a positive effect in hospitals, by reducing patient stress and recovery times

A US study demonstrated that the sunlight in hospital rooms modifies a patient’s psychosocial health, quantity of analgesic medication used, and pain medication cost.

Patients undergoing cervical and lumbar spinal surgeries were admitted to the bright or the dim side of the inpatient surgical ward post-operatively. A study found that patients exposed to an increased intensity of sunlight experienced less perceived stress, less pain, took 22% less analgesic medication and had 20% less pain medication costs.

Improved Lighting and Recovery Times

Another US study showed that patients in brightly lit rooms have a shorter length of stay compared to patients in dull rooms. For example, patients hospitalised for severe depression reduced their stays by an average of 3.67 days if assigned to a sunny rather than a dull room overlooking spaces in shadow.

Circadian Lighting: the Future?

At the moment predictions of circadian effects can only be made on a broad and general basis

The next challenge for circadian science will be the ability to tailor lighting regimes to individuals’ precise requirements, in order to maximise their circadian health

This will take account of their unique diurnal rhythms, physiological make-up, work and leisure patterns and so on.

Circadian Lighting at the Cutting Edge

There are two important areas of scientific research where new circadian lighting solutions are essential pre-conditions:

1. Space Travel – obviously trips into space, even into orbit around the earth, involve a total disruption of the 24-hour diurnal cycle for astronauts.

On a long-term basis this could be health-destroying, unless artificial lighting regimes are developed to replace the day-night cycle at sufficient intensities to mimic daylight

NASA has been one of the major funders of circadian science research in the USA

Circadian Lighting at the Cutting Edge

2. Antarctic Research

Similarly researchers in the Antarctic research station, Halley IV (opened in 2013) experience 6 months of daylight and 6 months of darkness

Earlier research had identified the disrupted circadian rhythms of Antarctic scientists as a genuine health and well-being issue

As a result, special bed-head lighting units with intense blue light were developed for the new British research station (right) to compensate long-stay researchers for the lack of normal daylight

Thanks for reading

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ILP Presentation - The Circadian System and Lighting