Hao Luoxi Cao Yixiao | Evidence-based research and design practice on light environment for human settlement health

Abstract: Light has a wide impact on human vision health, biological rhythms, emotional cognition, metabolism and immunity through visual and non-visual biological effects. It is a key technology for human settlement health that is focused on the cutting-edge fields of architecture, optics, life sciences, environmental engineering and other disciplines. The article analyzes the healing effect of light in human settlements, explains the value and necessity of evidence-based research and design in creating a healthy light environment for human settlements, and demonstrates a series of explorations and practices of light and health carried out by the author team in Antarctic scientific research stations and medical and nursing buildings based on evidence-based theory, problem-oriented, built environment as the carrier, and the goal of realizing human settlement health, targeting people of all ages and various types of human settlements.

1. Introduction - Light and Human Habitat Health

On May 16, 2019 - the second "International Day of Light", Ms. Audrey Azoulay, Director-General of UNESCO, delivered a speech on the theme of "The understanding and application of light benefits all mankind". She pointed out that from the origin of the universe to various new technologies, from X-rays to radio waves, in many fields such as medicine, agriculture, energy, optics, etc., light shaping It has created the human world and achieved a leap in science and technology. Its natural functions and its application in science and technology are indispensable elements in the daily life of human society and the key to achieving the goals of the United Nations' 2030 Agenda for Sustainable Development [1].

From the ancient Egyptian times when people set up colored glass indoors and used the different colors of sunlight passing through the glass to illuminate the body to treat diseases, to 127 years ago when the Danish doctor Niels Ryberg Finsen won the Nobel Prize in Medicine and Physiology for his pioneering contribution to the application of light radiation therapy to treat lupus vulgaris, smallpox and other skin diseases, human beings have a long history of exploring light health. However, it is only in the past 20 years that light health has become an important research content in the subject of human settlements.

On the one hand, the rapid and leap-forward development of semiconductor lighting technology has enabled the large-scale application of LED light sources that are easy to adjust and scene customized; on the other hand, with the discovery of American scholar David Berson and others in 2002 The third type of photoreceptor cells in the human eye - the internal photoreceptor retinal ganglion cells "ipRGCs" [2] - has emerged. The visual and non-visual mechanisms of light are becoming increasingly clear. Humanity has entered the subdivision of healthy light environment research. It has expanded the research and design practice of light from space creation and visual effects to physiological regulation, emotional intervention and cognitive improvement. It also attempts to use light in space as a positive environmental element to improve the health and well-being of human settlements.





2. The healing effect of light in human settlements

Rapid urbanization has not only promoted social and economic development and improved people's living standards, it has also brought severe challenges to human settlements health. The deep aging of the population structure, the accelerating pace of social life, the increasing competitive pressure of work and study, and the frequent use of electronic smart devices have not only led to a series of visual health problems, but also increased the risk of various physical and mental diseases.

Starting from the source of health promotion, various health intervention technologies and techniques that actively adjust the state of failure Duanhe methods are in urgent need of exploration and development. Light is the main component of the physical environment of human settlements and has a multi-dimensional health effect of "visual-physiological-psychological". The WELL standard, which is generally recognized in the field of healthy buildings, and the nine basic elements of healthy buildings proposed by the Center for Climate, Health and the Global Environment at the Harvard School of Public Health both focus on light environment.

It is certain that through the reasonable setting of light quantity, spatial light distribution, light source spectrum, lighting strategy, as well as the customized design of lighting landscape and light art media interface, it is of great research significance to use light as a direct, effective, safe and side-effect-free active health intervention method for the living environment to eliminate the negative effects of environmental pathogenic factors.


2.1 Light environment and visual health

The impact of light on human health is divided into two aspects: visual and non-visual. More than 80% of the information about the external world that humans obtain is through visual channels [3]. Therefore, visual quality affects most behaviors and activities such as work, entertainment, communication, leisure, etc., and is closely related to the quality of life. are closely related [4]. The eyes are the most delicate organs of the human body. Adverse lighting conditions such as insufficient illumination, shadows, glare, stroboscopic flicker, and excessive visual information stimulation will not only lead to a decline in visual function, visual fatigue, and reduced work performance, but also hinder the smooth progress of activities. Their long-term cumulative effects can even cause myopia, accelerate macular degeneration, and cause irreversible visual damage. China invests a large amount of human and economic resources in protecting national visual health every year, and improving the lighting environment of human settlements is one of the key tasks.

There is a mutually reinforcing relationship between human visual function, visual work and light environment. A large amount of research has been carried out around matching the visual abilities of teenagers, adults, the elderly and other various groups of people with different operating conditions such as paper, video display terminals (VDT), fine processing and other light environment parameters to achieve optimal visual performance and visual comfort. With the unremitting efforts of academic organizations and researchers represented by the International Commission on Illumination (CIE) and American scholar Peter Boyce [5], people have studied illumination, brightness, visual field brightness distribution, light source light color and color rendering. There is a growing consensus on the impact of individual light environment factors such as sex on visual quality. Domestic and foreign industry standards and specifications have been introduced one after another to guide the design practice of architectural light environment.

2.2 Light and biological rhythm

There is a special clock called "biological rhythm" in the human body, which regulates most physiological processes such as sleep, eating, metabolism, hormone secretion, and immune response, and maintains the healthy homeostasis of the body [6].

Biological rhythm disorders not only cause obesity, cancer, neurodegeneration and other diseases, but also affect the treatment and recovery of diseases. Light is the most important timing factor for human biological rhythms. In addition to cones and rods, the third type of photoreceptor cells present in the mammalian retina—retinal specialized photoreceptor ganglion cells (ipRGCs)—are photosensitive and can directly sense light stimulation and project light signals to the rhythm control center—the suprachiasmatic nucleus (SCN) [7]. They form a non-image visual pathway of light, affecting the secretion of important human hormones such as melatonin and cortisol in the pineal gland. To achieve the regulation of biological rhythms [8].



The rhythmic effect of light is the core focus of human health light environment research practice. All kinds of living places such as classrooms, offices, hospitals and underground spaces have introduced all-weather dynamic rhythm lighting systems to improve the quality of people's sleep at night and their mental attention and alertness during daytime awakening. Rhythmic stimulation has become a key indicator of a healthy light environment, and the quantitative evaluation of its impact is currently a new focus in related fields at home and abroad.

2.3 Emotional effects of light

On the one hand, American practicing physician John A. Schindler pointed out in his book "How to Live 365 Days a Year" [9] that up to 76% of diseases are related to bad emotions. Regulating emotions through reasonable methods and maintaining an optimistic and positive attitude are the keys to preventing and treating diseases and promoting physical and mental health. Bright white light therapy was introduced for seasonal affective disorder in the 1980s The results of subsequent clinical studies also show that light has a positive effect on the treatment of postpartum depression, premenstrual syndrome, and non-seasonal affective disorder.

On the other hand, the visual environment formed by light, color and space conveys emotional language, making light closely related to human cognitive and emotional experience. John Flynn, a pioneer in lighting psychology research, proved that changes in the light environment will cause different reactions in people's sense of space, visual clarity, privacy, pleasure, relaxation, and complexity. The visual impact of light and color is often used to create spatial situations and atmospheres to arouse emotions and induce specific psychological feelings. For example, James Turrell's series of immersive light art works construct emotional experiences from psychedelic to surreal through sensory resonance in the situation.



3. Evidence-based research on healthy light environment

3.1 The value and necessity of evidence-based research

Although there is a strong scientific basis behind the practice of light health, its demonstration application is difficult. On the one hand, due to the significant individual characteristics of the research subjects, various groups of people at different stages of life - children, teenagers, the elderly, pregnant women, and patients - have different physiological and psychological characteristics and their own healthy lighting needs; on the other hand, due to the intricate interactions between people and various elements of the built environment, it is difficult to directly apply the light health mechanism learned in the laboratory to the architectural space, and the actual health improvement effect of the design scheme is difficult to predict.

Evidence Based Research (EBR) and Evidence Based Design are interdisciplinary design ideas born on the basis of evidence-based medicine and environmental psychology. They emphasize obtaining empirical evidence through scientific research methods and statistical data, so as to make decisions and achieve the best results.

Therefore, evidence-based research and design are the only way to transform light health theoretical research into applied practice. it starts with a question As a guide, through empirical research in application scenarios, the optimal lighting design parameter combination is determined, and continuously revised and optimized during the put-in-use process, so that various specific light environment health goals can be achieved. The evidence-based strategy that runs through the entire process of research, design, application, and evaluation becomes a yardstick to help designers get out of the fog, making each node of the design plan rational and evidence-based. It also increases the uniqueness and pertinence of the design, so that every decision can bring maximum health benefits.




3.2 Evidence-based practice of whole-chain healthy light environment design

Evidence-based research and design of healthy light environment is a systematic process based on observation and experimental research, collecting evidence, testing hypotheses, and seeking the best solutions. It includes five key links: research and demand analysis, evidence-based experimental research, daylighting and lighting system development, testing and certification, demonstration application, and post-use evaluation (POE).


●Research and needs analysis

Survey Research and needs analysis is an important basic work for the evidence-based practice of light health. It aims to comprehensively and systematically understand the current status of the light environment in the target space and the behavioral, physiological and psychological characteristics of users through multiple channels such as literature research, actual data measurement, longitudinal follow-up observation, and questionnaire interviews, so as to sort out current problems and healthy light adjustment needs, and clarify the intervention goals for light health.

●Subjective and objective evidence-based experiments

The light health evidence-based experiment is carried out on the basis of a large number of existing theoretical studies. It aims to quantify the changes in visual performance and physiological and psychological indicators of personnel under different lighting conditions through experimental research methods that combine subjective and objective methods and mutual verification, and obtain a combination of lighting parameters that can improve physical and mental health, and provide scientific basis for subsequent research and development of daylighting and lighting systems and light environment design work.

In order to create a high-fidelity experimental scene with a sense of presence, obtain research conclusions with ecological validity, and provide guidance in application practice, the author's team (hereinafter referred to as the "team") built a full-scale experimental room. The indoor space layout, interface materials, and decorative furnishings are based on the actual target application environment. Realistic restoration, while recruiting target users as subjects. Experimental research targeting special groups such as the elderly with dementia and cancer patients has introduced virtual reality (VR) technology as a means of displaying lighting scenes. The immersive experimental scene presentation gives the subjects an immersive subjective experience, allowing experimental research that was previously impossible to carry out due to the subjects' mobility impairment to be carried out as usual.



In order to quantify the impact of light environment on human health as scientifically and accurately as possible and obtain reliable parameters, the team improved the traditional experimental method of purely subjective evaluation and tried to combine objective methods such as melatonin and cortisol hormone time bioanalysis and detection of brain electrophysiological signals with subjective scales to collect human performance data involving multiple complex physiological and psychological processes such as rhythm oscillation, emotional cognition, performance and fatigue through "multiple methods of simultaneous measurement and mutual verification".

●System development and testing certification

Based on a number of evidence-based experimental results, the team completed the research and development of a "healthy lighting system aimed at improving mood and rhythm" , systematically integrating various healthy lighting intervention technologies to form standardized, serialized, modular and universal products that can be flexibly applied in various living spaces.

The system consists of three modules: rhythm regulation, emotional intervention, and intelligent control. The rhythm module simultaneously meets the dual lighting needs of high-quality indoor functional lighting and rhythm regulation. On the basis of not changing the chromaticity coordinates and illuminance of the light source in the visual comfort light environment, light stimulation with a rhythmic effect is provided through spectral adjustment. The emotion module applies two patented technologies, "optical medium layer and media interface construction technology based on the optical medium layer" and "illumination emotional effect media interface display technology", to present high-quality artistic images on the low-pixel LED base layer, and to achieve emotional lighting media image customization for specific groups of people and specific environments. The intelligent control module has a built-in programmable controller that can accurately control various technical parameters such as light intensity, light time, light duration, light source color temperature, and spatial light distribution to achieve targeted dynamic control of artificial health lighting targets.

Testing and certification are also a necessary part of light health evidence-based practice to ensure Long-term safety and reliability of daylighting and lighting systems. The developed lighting products, accessories and control equipment need to be entrusted to a third-party testing agency authorized by the state for testing. They must pass the photobiological safety assessment, obtain a testing certificate, and undergo project engineering acceptance and completion acceptance by relevant units before being put into use [10].



● Demonstration application and post-occupancy evaluation

The long-term cumulative impact of the light environment on health and the evaluation of health effects are completed in the demonstration application and post-occupancy evaluation (POE). POE scientifically and rigorously evaluates healthy light environment projects that have been applied and operated for a period of time through objective means such as questionnaires, interviews, work meetings, and environmental monitoring. The purpose of carrying out POE work is not only to form a complete information feedback system and comprehensively and objectively evaluate research and design results, but also to provide theoretical and data support for the subsequent conduct of other evidence-based research projects and the formulation of relevant standards and specifications.

4. Healthy design of light and space

4.1 Health-supporting lighting technology for extreme environments - Healthy light environment transformation of Antarctic Research Great Wall Station and Zhongshan Station

The harsh natural environment of severe cold, heavy snowfall, and strong ultraviolet rays in Antarctica, as well as the special social environment of closure, isolation, and restricted movement, have brought double challenges to the physical and mental health of the expedition team members. Physical and psychological symptoms such as overwintering syndrome, polar T3 syndrome, and poor sleep quality have seriously affected the quality of life of the scientific expedition team members and hindered the smooth progress of the scientific expedition mission. The distinctive characteristics of the light and visual environment of the Antarctic continent are the main causes of rhythm and emotional problems among scientific expedition team members.