1. Human Centric Lighting
Prepared by ISR – University of Coimbra
July 2017

2. Human Centric Lighting
Summary:
Circadian Rhythm
Advantages to human performance and health

3. 1. Circadian Rhythm
Light varies during the day according to the natural lighting cycle:
Low light levels and low CCTs (Correlated Colour Temperature) in the early morning
High light levels and high CCTs at midday (up to 10,000 K)
Low light levels and low CCTs during evening
Extremely low light levels and a medium CCT under moonlight

4. 1. Circadian Rhythm
These natural variations of sunlight help determine the timing of our internal clock called the circadian rhythm telling our bodies when to sleep and when to be alert.
Because our sleep-wake cycle is so important, its deregulation may also effect:
Immune system
Memory
Behavior

5. 1. Circadian Rhythm
Circadian derives from the words circa dies meaning "about a day" and is linked to the cyclic system where the human body adapts to the rhythmic of active and passive periods (for humans that is the day respectively nights) over a period of circa 24 hours.
The Human Circadian System is fundamental to our physiology and controls much of our behaviour.
The steady electric light we typically have in our offices and homes can throw off our eternal clocks and cause issues with sleep.

6. Most of the time spent working and on indoor activities!
1. Circadian Rhythm
The lack of exposure to the sun’s spectrum can interfere with the body’s natural cycles.
9% Other
36% working
Most of the time spent working and on indoor activities!
On a sunny day lux
Although light is so importante to humans, nowadays we spend 90% of our times indoor, even children. That makes that the indoor environmental becomes paramount of our general sense of well-being and health.
The indoor light conditions however do not deliver the light nutrition that people need to stay healthy in life time. A sunny outdoor day provides 100,000 lux and a cloudy day still provides 10,000 lux.
Indoors light levels are no even a half of that.

7. 1. Circadian Rhythm
Today there is a disconnect between natural and artificial light with regard to intensity, color and dynamics of light
Too little light during the day
Too much light during the night
Besides receiving too little light during the day, we receive too much light in the evening and night. The presence os light during the evening and night delays our sleep onset. The lack of light during the day combined with too much light during the evening causes some consequences. One of them is sleep deprivation. Instead of 8 hours sleep at night that a lot of us need, we now get an average of around 6,5 hours that is not enought. Diseases and a lot of information can be foud on the negative effects of sleep deprivation, on emotion cognitive and social responses.
Consequences
Poor circadian synchronisation, problems with body clock similar to jet-lag
Problems with sleep & alertness
Disturbance of the hormone system
Compromised mood, productivity, well-being and health

8. 1. Circadian Rhythm
Human Centric Lighting seeks to enhance human performance, comfort, health and well-being by balancing visual, emotional and biological benefits of lighting for humans. Light affects our vision, body and emotions
Therefore, lighting design should take into account:
Functional light
Optimal lighting conditions for the performed task creates optimum light confort and improves concentration, creativity and performance.
Biological light
This is also referred to as circadian light and is designed to support the sleep-wake cycle of people using dynamic approaches to control and adapt the spectral content, intensity, duration and timing of the light during the day and night time.
Emotional light
Providing an environment that gives us a perception of comfort or safety.

9. 1. Circadian Rhythm
Body response to light Recent discovery of intrinsically photosensitive retinal ganglion cells (ipRGC) in our bodies show these are very important in setting the internal clock. The newly identified ganglion cells respond most sensitively to visible blue light and set the internal clock that synchronizes our bodies with the external cycle of day and night. Light that is rich in blue content stimulates the ipRGC photoreceptors, make the pupils smaller, encourages dopamine, serotonin, and cortisol production but suppresses melatonin.
The retina of the human eye is not only made up of rods and cones which predominantly serve visual perception but also intrinsic photosensitive retinal ganglian cells (ipRGC). In 2007 it was discovered that these cells contain melanopsin and are therefore sensitive to light. The maximum sensitivity for the melanopic effect of light is at a wavelength of 490 nm (blue). That means that melanopsin is especially well stimulated at this wavelength.
The effect of this stimulation is that a suppression of the production of the hormone melatonin takes place in the pineal gland. The hormone melatonin plays a central role in the circadian rhythm of man. Especially in the evening, when we are tired, our blood has a high concentration of melatonin which drops as we sleep so that the melatonin level is considerably lower in the morning. Daylight, with its high proportion of blue light (especially in the morning), also contributes to the suppression of melatonin.

10. 1. Circadian Rhythm Melatonin suppression
-The retina of the human eye is not only made up of rods and cones which predominantly serve visual perception but also intrinsic photosensitive retinal ganglian cells (ipRGC). -In 2007 it was discovered that these cells contain melanopsin and are therefore sensitive to light. The maximum sensitivity for the melanopic effect of light is at a wavelength of 490 nm (blue). That means that melanopsin is especially well stimulated at this wavelength. -The effect of this stimulation is that a suppression of the production of the hormone melatonin takes place in the pineal gland. The hormone melatonin plays a central role in the circadian rhythm of man. Especially in the evening, when we are tired, our blood has a high concentration of melatonin which drops as we sleep so that the melatonin level is considerably lower in the morning. Daylight, with its high proportion of blue light (especially in the morning), also contributes to the suppression of melatonin.

11. 1. Circadian Rhythm Hormones that control the biological rhythm
The ganglion cells send signals to the brain and regulate hormone production. The four most important hormones that control the biological rhythm are:
Melatonin makes you tired, slows the body functions and lowers activity in favour of rest.
Cortisol on the other hand is a stress hormone that is produced from about 3 am. It stimulates the metabolism and programs the body for day mode.
Serotonin works as a stimulant and motivator. While the cortisol level in the blood drops throughout the day and thereby acts counter-cyclic to the melatonin level, serotonin helps elevate energy levels.
Dopamine plays an important role in muscle coordination, alertness and the pleasure system

12. 2. Advantages to human performance and health
Source: licht.de

13. 2. Advantages to human performance and health
Illuminance
Increasing the illuminance on the task produces an increase in performance.
The visual acuity depends on the intensity of light: about 40% increase when going from 50 lux to 500 lux.
Enhances concentration and alertness
Low illuminance increases eye fatigue
Studies suggest that even relatively low illuminance levels (~150 lx at the eye) are sufficient to induce alertness and shift a free-running circadian rhythm.

14. 2. Advantages to human performance and health
Color Temperature
Higher color temperatures (over 5300K) activate the brain and promote concentration
Lower color temperatures induce relaxation and calm.
Less fatigue at higher temperatures (eye becomes tired less quickly at 6000K than 2700K)

15. 2. Advantages to human performance and health
Color Temperature
As color is closely linked to mood that causes psychological reaction, color temperature of light is critical.
High Colour temperatures (e.g K or above) are perceived as “cool white” (blue and green tones)
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Lower Colour temperatures (e.g K) appear to be “warm” (yellow and red tones)

16. 2. Advantages to human performance and health
Light Color
Green is the most reassuring colour. It creates a feeling of stability, but only when used in soft tones.
Orange is a strong stimulus. It is very social, but also contributes to activity.
Red symbolizes activity and passion; it can also stimulate apetite.
Pink is the colour of feminity and has a physically soothing effect.
Purple can provoke a feeling os spirituality, but may be perceived very differently - positively or negatively - by different people.
Blue has a mentally calming effect and serves perfectly to sooth anxiety, especially when warmer tones of blue are used.
triangles represent the colors in the right points

17. 2. Advantages to human performance and health
Light Distribution
Bright planar lighting in the upper part of the visual field (such as a bright sky) more effectively stimulates ganglion cells.
This is achieved with :
large windows, skylights and daylight control systems for brightening the ceiling;
large-area luminaires or luminous ceilings;
luminaires casting indirect light over large areas, so that the ceiling and the upper third of the walls are illuminated;
back-lit transparent materials such as luminous ceilings, skylights with artificial light, light boxes or net curtains;
lighting with indirect light components on room elements and furnishings.

18. 2. Advantages to human performance and health
Individualized maximization of concentration and energy.
Improved task performance and productivity.
Improved error rates.
Reduced stress level and sick leave.
Increased employee motivation and commitment.
Improved safety and productivity in the workplace.
Biorhythm adjustments for night shift workers.

19. 2. Advantages to human performance and health
Advantages to health
Improved circadian rhythm
Improved quality of sleep
Increased emotional stability and lower rates of depression.
Improved immune system
improved staff productivity
Reduced sick leave amongst staff

20. 2. Advantages to human performance and health
Applications: Education
Schools are an excellent location for tuneable white light features. Here the light is used not only to control daily rhythms for pupils and staff, but also to improve alertness during tests and concentration tasks.
The teacher may switch on an intensive, cool white light during these activities, or a warm white, dimmed light for relaxation and group talk.
The right light in the morning, with sufficient brightness and blue-enriched, can help to get you ready for the day.
It doesn’t matter if the person is an elementary scholar or a teacher. Both can benefit from an optimized lighting environment in a direct or indirect way. 

21. 2. Advantages to human performance and health
Benefits
During the early morning hours, the right light can help to wake up with less sleepiness.
A better light environment can improve alertness and concentration during learning.
Lighting systems that give higher light intensities and color temperature at the right time can help to improve duration of sleep and quality of sleep and thus improve learning effects.
source: easylume

22. 2. Advantages to human performance and health
Applications: Healthcare
In hospitals and elderly care centres, residents often suffer from less access to daylight because of illness or mobility issues. Spending long time indoors may disrupt sleep patterns.
Healthcare environments are well suited to implement lighting cycles containing sunrise, sunset and daylight simulations.
The effects on the patients or residents are higher activity levels during daytime, better sleep at night, shorter recovery times and reduced intake of anti-depressants.
source: lightingforpeople

23. 2. Advantages to human performance and health
Benefits to the residents:
Prevent mood fluctuations and depressions.
Stabilization of the circadian rhythm.
The emotional and physical well-being improves as a result of restful nights.
Reduction of sleep-inducing drugs.
Benefits to the staff:
Lack of daylight is balanced and counteracts insomnia.
Improved well-being of the employees.
Freeing personnel because residents experience activity and resting phases at the right time.
More relaxed in the evening with fewer headaches and less tired eyes.
Motivation of staff by knowing that the residents are given individualized care.

24. 2. Advantages to human performance and health
Applications: Offices
Humans spend most of their time awake indoors. That makes office areas excellent places to implement Human Centric Lighting solutions. Such solutions can bring increased energy and motivation to employees.
For countries with little daylight during the winter months, “tuneable white light” luminaires may reduce winter depressions and other seasonal emotional disorders. The same lighting settings may also give short-term concentration and alertness effects, when applied correctly.
Workplace lighting can, in addition to providing sufficient light to conduct work-related visual tasks, affect employees’ alertness, mood, cognition, sleep-wake pattern and health.

25. 2. Advantages to human performance and health
Benefits
Exposure to more intense light may boost employees’ feelings of alertness and vitality during daytime and at night.
Circadian effective light exposure during the daytime may have a positive effect on office workers’ sleep during the subsequent night.
The light settings can influence employees’ appraisals of the lighting and the working environment.
Individuals’ preferred light settings show substantial variations. Individual lighting control will affect job satisfaction positively.