What influence does light have on living beings? Can light be designed on a human scale? Why is it necessary for a lighting design to be drawn up by a professional? What is meant by circadian rhythm?
Until recently it was believed that lighting should only meet the needs of optimal vision, without considering that light significantly affects the performance, mood, biological rhythm and cognitive functions of individuals, making them feel comfortable and contributing to a better life.
This is what Human Centric Lighting (HCL) is all about – how to optimise the biological and emotional influence of light on people by placing the human being at the centre of the lighting design, tailoring lighting solutions to contribute to the well-being of those who live, work and frequent certain environments. The visual, emotional and biological spheres represent the three spheres influenced by light and lighting to which designers must pay attention.
Seeing, being able to find one’s way around and reading light signals (such as emergency lights) are fundamental aspects to consider when designing ambient lighting, so much so that there are well-codified regulations and standards.
The biological aspect has to be considered very carefully, as influencing the circadian rhythm can help achieve greater productivity during the day and improve sleep at night. A well realised lighting design avoids subjecting individuals to negative biological effects from inadequate or even harmful lighting.
For this to happen, all the professionals involved (architect, engineer, light designer and system integrator) must be coordinated, including the evaluation of materials and products used. The initial phase of the project is already developed with an interdisciplinary approach. Whenever possible, it is very important to make use of natural light, which must then be supplemented with artificial light. Fundamental is the dynamic transition from one lighting scenario to another (morning, day, evening, night) also linked to the changing seasons and changing weather conditions.
Circadian rhythm: what it is
The circadian rhythm is a complex system that regulates the biological rhythms of all living beings in relation to the environment. Variations in physiological parameters such as temperature and blood pressure in mammals, the shedding of leaves in autumn, the blossoming of certain plants in spring, or the alternation between sleep and wakefulness in animals, are events controlled by internal clocks in response to environmental changes caused primarily by the Earth’s rotation.
Referring to people, the circadian rhythm is typically linked to their biological clock and indicates the sleep-wake cycle and changes in human physical parameters that occur over the course of a solar day (24 hours).
The circadian rhythm depends both on external elements such as the Earth’s rotation – and consequently the alternation of day and night – and on factors internal to the individual. During the 24-hour period, variations involving the circadian rhythm are not only related to the sleep-wake cycle, but also affect other fundamental elements of the individual: metabolism, hormones, blood pressure and body temperature. There is a very close correlation between sleep quality and an individual’s state of health: those who suffer from insomnia are prone to states of stress, due to hormones released during the night, resulting in the risk of high blood pressure.
Light regulates the circadian rhythm
Light plays a decisive role in the regulation process of the biological clock. Each sleep/wake phase is reset by the presence of light to be synchronised with the day/night cycle. In practice, light (sunlight or artificial light) transmits a signal to the brain, which in turn induces the production of melatonin, called the sleep hormone, characterised by variable production during the day, with the peak occurring at night. The presence of melatonin in the blood induces relaxation and sleep, while its absence increases alertness and attention.
Exposure to light upon awakening causes the suppression of melatonin and the production of cortisol (the hormone responsible for stress) leading to an increase in performance, while exposure to light in the first half of the night delays the circadian rhythm, preventing relaxation and sleep, and exposure in the second half of the night anticipates the circadian cycle.
The introduction of artificial lighting has caused the alteration of the natural light-dark alternation: we live most of our days indoors (school, office, factory) where we receive insufficient or even inadequate light stimuli: places where we sometimes do not notice what the weather is outside or what time it is. Even during the night hours we are stimulated by TV screens and mobile phones, in addition to conventional lighting. This is a negative element in the regulation of our biological rhythms. The most frequent complaints related to poor lighting quality range from burning eyes, tearing, dry eyes, tiredness when reading, vision problems (blurred or double vision), pronounced photosensitivity, headaches to sleep disorders. If we then talk about alteration of the circadian rhythm, the disorders can be cardiovascular, metabolic or gastrointestinal disorders, psychological problems related to stress, anxiety, depression, increased risk of cancer.
This is why the correct – and differentiated – light in the various environments, depending on the activities taking place there, is essential. The technical aspects to be taken into consideration in order to correctly implement a lighting design are smart lighting (using sensors and control systems), tunable white (i.e. variation of intensity and colour temperature) and customisation, based on the needs of individuals and the intended use of the rooms.
SCHOOLS
Ideally, natural light should be used as much as possible, supplemented as needed with LED lighting that mimics natural light as much as possible. It is crucial when planning to consider the orientation of the building and its location. The correct level of lighting in the early hours of the morning helps students to wake up and reactivate, and a bright environment increases the level of attention and concentration during lessons. Intensity and high colour temperatures improve sleep duration and quality, and better sleep translates into better learning.
WORKING ENVIRONMENTS
Illuminance levels that are too low prevent our circadian clock from remaining synchronised. If we consider that the illuminance level outdoors, in sunny conditions, is 80,000-90,000 lux, and in shaded conditions, 5000-9000 lux, while inside an office, the illuminance on the work surface is around 500-1000 lux… we realise how crucial special attention to lighting design is in order to achieve a real improvement in the quality of life of workers.
The objectives when designing lighting for workplaces are:
- to support the performance required according to the activity carried out;
- to encourage vision, concentration and computer work
- facilitate interaction between people
- to make a workplace safe
- spreading a positive mood
- ensure flexibility and optimisation within everyone’s reach
- avoid malaise and discomfort
- ensure harmonisation with the different times of day, weather conditions and seasons.
SPECIAL CONDITIONS
It takes more than an eye for detail to design lighting in atypical environments, think of workers working night shifts in factories or airline pilots and crews engaged on intercontinental routes. Studies and research confirm that in-flight lighting can help alleviate jet lag and the severe fatigue caused by long plane journeys, which also benefits the passengers, which is why in-flight lighting is currently designed with reference to specific combinations of red and blue light colour spectra that stimulate/suppress melatonin production, regulate sleep-wake rhythms, help synchronise biorhythms with the destination and reduce the effects of jet lag.
CONCLUSIONS
Correct lighting design is the basis for high lighting quality. The designer’s objectives must be: to achieve optimal visual conditions without glare or flickering, to use as much natural light as possible with adequate shading systems when necessary, to create pleasant environments in which people tend to stay, to improve well-being, performance and productivity, and to protect health.