The human reaction to light

A new understanding of the links between light and health have led to ‘humancentric’ lighting, which boosts vitality, promotes well-being and enhances productive capacity and concentration. Peter Hunt from the Lighting Industry Association explains more

No-one can have failed to notice that inefficient light sources have been phased out over recent years paving the way for new, more efficient technologies. The need to reduce our energy consumption in the face of rising prices and scarcity of supply along with intelligent use of daylight is now widely accepted.

Growing importance is attached to good efficient lighting in educational establishments incorporating modern light sources and luminaires incorporating intelligent control systems for optimal use of daylight.

In a modern intelligent lighting system sensors monitor the daylight levels and adjust the artificial lighting which saves energy.

Presence controls can detect when people enter or leave a room and switch lights off when not required. The adoption of these controls alone can reduce energy consumption by as much as 50 per cent without taking into consideration the fact that modern LED lighting is already considerably more efficient that previous technologies and lasts much longer thereby reducing replacement and maintenance costs.


There are still a great many outdated inefficient lighting installations in use today however. Over time accumulation of dirt and ageing of materials can halve the light output of older lighting installations.

The payback period for switching to a more efficient modern system is often just a few years but the advantages go further than simply energy efficiency.

Light is good for us, all human life depends on light and as the clocks go forward in Spring, we enjoy more of it, feel invigorated and generally more cheerful.

This tells us that we need light for more than just vision. Light controls the internal clock that controls our bodies in a 24 hour rhythm. Without light as a cue our internal clock become out of sync resulting in lethargy, tiredness, mood swings and in some cases even a weakened immune system.

For many years it has been known that the eye contains two types of receptor, rods and cones which react to light and enable vision. A relatively recent discovery by scientists is a third receptor which reacts to light but is not linked to vision.

These receptors are particularly reactive to light with a blue content and they are responsible for setting our internal clock or circadian rhythm.

This discovery has spawned a new understanding about light and health and today the use of ‘humancentric’ lighting as it has become termed, can supplement daylight as required and support the human sleep/wake cycle, boosting vitality, promoting well-being and enhancing our productive capacity and concentration.


You can start to see why this is of particular interest in the teaching environment. Modern education is about encouragement and challenge. Much of the learning process is visual so it is logical that good lighting plays a crucial role in creating the right environment for learning.

The non-visual effects of lighting can be classified into three groups – feelings, functioning and health. Feelings include our mood, vitality or state of relaxation.

Functioning refers to our state of alertness leading to increased concentration and vigilance and cognitive performance including memory, comprehending languages, reasoning, problem solving, creativity and decision making.

Health effects relate to the sleep-wake cycle, the rhythm of rest and activity controlled by our biological clock which is essential for optimised functioning by day and good recovery sleep by night.

SAD, ADHD and schizophrenia have all been linked to biorhythmic disturbance. Studies have shown that during winter months up to 40 per cent of northern Europeans suffer from lack of drive and mood swings that can develop into depression.

In schools, specific lighting solutions can significantly improve concentration and cognitive performance and lead to improved test results. Research carried out in Sweden suggests that error rates dropped from a first to a second test by about 45 per cent (comparison group with conventional lighting only 17 per cent) and cognitive speed improved by nine percent (comparison group only five percent).

In addition, such lighting solutions can reduce motor restlessness, support alertness in the morning and improve social behaviour. Furthermore healthcare costs were reduced by 10 per cent due to reduced ADHD effects, efficacy of treatment for mental disorders improved by 18 per cent and staff turnover was reduced.


We spend on average around 87 per cent of our time inside buildings much of it under artificial light which lacks the dynamism of natural daylight.

It therefore seems logical that we should emulate the effect inside the built environment. We know that the colour and amount of light we use and how long we are exposed to it are important considerations.

Daylight is not static, it changes throughout the day. It produces bright blue-rich light in the morning to send us a ‘wake up’ signal but exposure to that same blue light at night can be disruptive to sleep.

In the evening daylight provides a lower level warm light which prepares us for rest. Light is a form of medicine and we should use it wisely.

This understanding is relatively new but already researchers are able to develop light ‘prescriptions’ that can alleviate symptoms of Alzheimer’s disease and help reduce depression.

A little more about the human circadian rhythm. Shortly before we wake, our body temperature, blood pressure and pulse rate rise. After about an hour the body begins the production of stimulating hormones and this is the time of day when our ability to solve brain teasers like Sudoku, for example, is at its best until about noon.

Naturally this is also the best time for exams or assessment tests. Between noon and 2pm the production of stomach acid peaks which aids digestion of the midday meal, however, this process consumes so much energy that the body feels fatigued afterwards.

Even if we skip lunch, the body still experiences a performance low. In the early afternoon our body and minds begin to pick up again and those engaged in sport, for example, between 4 and 5pm will derive more benefit than at any other time of the day. As the evening progresses we begin to feel tired and sleep follows.


Following the discovery of the third receptor in the eye, experiments showed that a particular colour of light surpressed production of the ‘sleep hormone’ melatonin by sending a message to the hypothalamus.

Melatonin makes us feel drowsy and slows down bodily functions and activity to facilitate a good night’s sleep. It also slows down a number of metabolic processes and reduces body temperature ahead of the release of growth hormones which aid cell repair while we sleep.

In the morning light triggers the third receptors to send a message suppressing the production of melatonin in the pituitary gland while the pituitary steps up production of another hormone called serotonin.

Seratonin works to elevate our moods and motivation, helping us to achieve performance peaks throughout the day. If our body receives insufficient light during the day we do not produce enough melatonin to support a good night’s sleep.

Returning to artificial light there is evidence to suggest that ‘light showers’, short bursts of blue rich light, can have an energising effect and promote concentration at certain times of the day and studies have shown this concept can deliver positive effects in schools.

Recent technology advances in LED lighting enables the lighting industry to support the move to dynamic interior lighting as luminaires fitted with appropriate controls can deliver a wide range of white light tones.

This allows a simple and efficient switch from cooler blue tones that promote concentration to warmer tones that sooth and help us relax, all the time responding to changing daylight levels.

More research is clearly needed but as our understanding of the human reaction to light improves so does the need to consult specialist lighting designers to ensure the right system is installed to match the requirements of a space.

For too long energy efficiency has been the driving consideration in lighting installations in the teaching environment but now we can provide a better lit environment to enhance the well-being and performance of teachers and students alike.

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