Elsevier

Physiology & Behavior

Volume 228, 1 January 2021, 113195
Physiology & Behavior

Review
Non-visual effects of indoor light environment on humans: A review

https://doi.org/10.1016/j.physbeh.2020.113195Get rights and content

Highlights

  • The comfortable and healthy lighting environment contribute to human health and well-being.

  • Understanding the effects of environmental lighting regulation on humans is crucial.

  • Research on light-induced non-visual effects contains circadian rhythm, alertness, and mood.

  • How light intensity and spectral changes have non-visual effects is summarised and provided.

  • Investigations of times of day and duration, need to be further considered and analysed.

Abstract

As a result of the desire to improve living standards, increasing attention is paid to creating a comfortable and healthy lighting environment that contributes to human health and well-being. It is crucial to understand the effects of environmental lighting regulation on humans’ physical responses and mental activities. In this review, we focus on the scientific research on light-induced non-visual effects on humans, providing a systematic review of how the quantity of light, spectral changes, time of day, and duration have effects on the circadian rhythm, alertness, and mood based on eligible literature. The key findings are as follows: (1) The increase of illuminance and correlated colour temperature (CCT) at night were both positively associated with melatonin suppression, thus affecting the circadian rhythm. Meanwhile, a high CCT is conducive to the stimulation of positive mood. (2) Blue light and high CCT light at night induced delayed phase shift, and the objective alertness was reduced under the condition of lack of blue components. (3) High illuminance was positively correlated with subjective alertness during daytime, and increased the positive mood in the morning and decreased it in the afternoon. These findings serve as an important reference for stakeholders to optimise lighting in constructed environments to improve health and well-being considering the non-visual effects above and beyond visual performance.

Introduction

As an important characteristic of indoor environment, light affects human health and well-being [1]. Increasingly more human activities are confined to indoor environments, which are vulnerable to the influence of various light sources, including light-emitting diodes (LEDs) as a part of new generation lighting products. As a result, increasing attention has been paid to creating a comfortable and healthy lighting environment in offices, classrooms, or homes due to intense work and social interactions [2, 3]. Utilising modern lighting control technology to sufficiently provide humans with psychological and physiological comfort is an important means to improve their work efficiency and well-being [4], [5], [6].

Light is one of the significant factors in people's daily lives and is involved in most human activities. When visible light (electromagnetic spectrum between 380 nm and 780 nm) enters the eye and reaches the retina, a complex chemical reaction occurs in the photoreceptor cells; rods and cones. The reaction is termed phototransduction. Light activation causes a graded change in membrane potential and a corresponding change in the rate of transmitter release onto postsynaptic neurones [7]. When visual information leaves the retina, it is sent via the optic nerve to the dorsal lateral geniculate nucleus in the thalamus, and then transmitted to the primary visual cortex, which is located in and around the calcarine fissure in the occipital lobe, thus causing vision [7]. However, photoreception in the eye leads not only to vision but also to effects on human physiology, behaviour, and mood, often summarised as non-visual effects of light [8]. It is also known as non-image forming effects in the literature. In 2001, Thapan et al. [9] and Brainard et al. [10] demonstrated evidence of non-rod non-cone photoreceptors. Since the discovery of intrinsically photosensitive retinal ganglion cells (ipRGCs) by Professor Berson from Brown University in 2002 [11, 12], the non-visual effects of light on humans have aroused much attention. These ipRGCs were first recognised in relation to their role in regulating circadian rhythms, and ipRGCs also influence many other processes [8]. Researchers have created different lighting conditions in experiments to evaluate the magnitude of the non-visual responses through various biomarkers of the circadian system or indicators of human performance, such as melatonin suppression, phase shift and sleep quality, subjective and objective alertness, and mood [13]. These experimental studies serve as the basis for a better understanding of the non-visual effects and provide guidance for lighting designs and the operation of lighting systems that consider human health and well-being.

The light factors influencing non-visual effects have been discovered in laboratory experiments. After referring to two reviews [14, 15] and a modelling framework [16, 17], P. Khademagha et al. [13] summarised six factors triggering the non-visual light effects, including spectrum (spectral power distribution, SPD), quantity, directionality, timing, duration, and history, which are grouped into luminous and temporal categories. In 2016, the International Commission on Illumination (CIE) published a technical report on healthful interior lighting recommendations that delivered a research roadmap of questions for technical researchers [18]. Understanding the relationship between light exposure and its effects on the circadian rhythm, alertness, and feelings of well-being is the precondition for creating a healthy and comfortable light environment. This topic encompasses an interdisciplinary study of life science, ergonomics, and behavioural and cognitive neuroscience, and is aligned with traditional lighting. In recent years, the catchphrase “Human-Centric Lighting” (HCL) has come to describe lighting that is intended to address non-visual effects. With the birth of the concept of HCL, every user of a lighting system is considered individually in accordance with their age, profession, and current activity as well as external parameters, such as weather, time of day, and the presence of daylight [19]. Precisely, while considering the lighting quality and lighting biosafety, the individual needs for lighting should be taken into account in different situations at different times. Researchers generally believe that systematisation and a long-term strategy of ambient lighting are two key points and that human-centric lighting design and operation control will improve the productivity and health of individuals in the next generation of indoor light environments [19], [20], [21].

There are already several reviews focussing on lighting and health, which include non-visual effects. For example, Souman et al. [22] performed a systematic review of empirical studies between 1990 and 2016 on the acute alerting effects of light, and summarised important conclusions on the evaluation of effects when light intensity and spectral distribution were manipulated. Figueiro et al. [23] described recent applied and field research and summarised the lighting characteristics that affect the outputs of the circadian system in 2018, which helped lighting researchers and professionals to determine how it can be employed to maintain circadian entrainment. Khademagha et al. [13] presented a theoretical framework of the relationship between non-visual effects and light from the perspective of relevance in 2016, which enabled daylighting stakeholders to incorporate the non-visual light requirements into their design. However, there is no comprehensive analysis of the impact of specific light factors on three aspects of non-visual effects: circadian rhythm (melatonin suppression, phase shift, and sleep quality), subjective and objective alertness, and mood. The authors believe that this work will help to improve the light environment to meet the requirements of human health and well-being, and provide a reference for the application of health lighting technologies considering non-visual effects simultaneously.

In this work, we provide a review of the non-visual effects of indoor light environment on humans based on the existing literature. The impact of light intensity, spectral distribution, time of day, and duration on three aspects of non-visual effects, including circadian rhythm, alertness, and mood, are summarised and analysed according to scientific selection and induction. The findings have an important reference value for the optimisation of lighting in the built environment for both lighting design and lighting control. It can also prompt researchers in these fields of life science, ergonomics, and behavioural and cognitive neuroscience to further promote interdisciplinary integration for the demanding targets of building science, and provide more detailed experimental data and theoretical bases for the design and operation of the light environment.

Section snippets

Search procedure

The scope of the review was the previously reported research outcomes. The goal of this literature review was to summarise and integrate findings. A conceptual organisation was used to organise the review, and scholars and stakeholders were intended to be the audience.

The search focussed on two main concepts: non-visual effects and light. Therefore, the terms for searching included combinations of “non-visual effects” and “light*” or “non-image forming effects” and “light*”. The terms were

Aspects of non-visual effects

In the experiments of the selected publications, the non-visual effects of light on humans were evaluated based on different aspects. In this review, circadian rhythm, alertness, and mood were investigated because these three aspects were the most assessed aspects among the studies (63%, 63%, and 48%, respectively). The specific instructions are shown in Fig. 2.

In the circadian rhythm, melatonin suppression has been widely researched. When light hits the retina, the ipRGCs are activated by the

Results

In this review, four light factors are involved according to the literature selected in Section 2.2 Study selection. Two of the factors are included in luminous factors: quantity and spectrum (SPD). Different light manipulations were performed in the selected studies. For polychromatic white light, illuminance and CCT were changed; for monochromatic light, the intensity and wavelength were changed. The other two temporal factors are timing and duration. As indicated in the introduction,

Discussion

The quality of eligible studies was assessed through an assessment tool, and the criteria included study question, eligibility criteria and study population, outcome measures clearly described, valid and reliable, statistical analysis, etc. Although there are different technical differences in the same research objectives, the distribution rules of the conclusions are reasonable. However, owing to the problems of experimental conditions and methods, the research conclusions under certain

Conclusion

In this review, we focussed on the outcomes of light factors on three aspects of non-visual effects. Through 27 publications with strong relevance, circadian rhythm, alertness, and mood were investigated because these three aspects were the most assessed aspects among the studies (63%, 63%, and 48%, respectively). Each aspect based on four different light factors, especially quantity and spectrum, was scientifically summarised and analysed. The key findings are as follows:

  • The increase in

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Acknowledgements

This work was supported by the Fundamental Research Funds for the Central Universities under Grants 22120180189 and 22120170260, China.

References (96)

  • A. de Vries et al.

    Lighting up the office: the effect of wall luminance on room appraisal, office workers’ performance, and subjective alertness

    Build. Environ.

    (2018)
  • T.T. Ru et al.

    Non-image forming effects of illuminance and correlated color temperature of office light on alertness, mood, and performance across cognitive domains

    Build. Environ

    (2019)
  • K. Smolders et al.

    A higher illuminance induces alertness even during office hours: findings on subjective measures, task performance and heart rate measures

    Physiol. Behav.

    (2012)
  • K. Smolders et al.

    effects on alertness, vitality, performance and physiological arousal

    J. Environ. Psychol.

    (2014)
  • M.G. Figueiro et al.

    The impact of daytime light exposures on sleep and mood in office workers

    Sleep Health

    (2017)
  • R.J. Lucas et al.

    Measuring and using light in the melanopsin age

    Trends Neurosci.

    (2014)
  • M.S. Rea et al.

    A model of phototransduction by the human circadian system

    Brain Res Rev

    (2005)
  • J.S. Carpenter et al.

    Psychometric evaluation of the pittsburgh sleep quality index

    J Psychosom Res

    (1998)
  • D.J. Buysse et al.

    The pittsburgh sleep quality index - A new instrument for psychiatric practice and research

    Psychiat. Res.

    (1989)
  • K. Kaida et al.

    Validation of the Karolinska sleepiness scale against performance and EEG variables

    Clin. Neurophysiol.

    (2006)
  • P. Graw et al.

    Circadian and wake-dependent modulation of fastest and slowest reaction times during the psychomotor vigilance task

    Physiol. Behav.

    (2004)
  • T.H. Monk

    A visual analog scale technique to measure global vigor and affect

    Psychiat. Res.

    (1989)
  • C. Cajochen et al.

    Evidence that the lunar cycle influences human sleep

    Current Biol.

    (2013)
  • T. Kruisselbrink et al.

    Photometric measurements of lighting quality: an overview

    Build. Environ.

    (2018)
  • Q. Dai et al.

    A proposed lighting-design space: circadian effect versus visual illuminance

    Build. Environ.

    (2017)
  • A. Borisuit et al.

    Monitoring and rendering of visual and photo-biological properties of daylight-redirecting systems

    Sol. Energy

    (2016)
  • L. Edwards, P. Torcellini, A Literature Review of the Effects of Natural Light On Building occupants, Report...
  • J.A. Veitch

    Light, lighting, and health: issues for consideration

    Leukos

    (2005)
  • P.R. Boyce

    Lemmings, light and health

    Leukos

    (2006)
  • Lighting - Well-Being and Performance at Work

    (2013)
  • M. Boubekri et al.

    Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study

    J. Clin. Sleep Med.

    (2014)
  • D. Purves et al.

    Neuroscience

    (2001)
  • CIE Position Statement On Non-Visual Effects of Light - Recommending Proper Light At the Proper Time, 2nd Edition,...
  • K. Thapan et al.

    An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans

    J. Physiol.-London

    (2001)
  • G.C. Brainard et al.

    Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor

    J. Neurosci.

    (2001)
  • S. Hattar et al.

    ganglion cells: architecture, projections, and intrinsic photosensitivity

    Science

    (2002)
  • D.M. Berson et al.

    Phototransduction by retinal ganglion cells that set the circadian clock

    Science

    (2002)
  • W.J.M. van Bommel et al.

    Lighting for work: a review of visual and biological effects

    Light. Res. Technol.

    (2004)
  • M. Andersen et al.

    A framework for predicting the non-visual effects of daylight - Part I: photobiology-based model

    Light. Res. Technol.

    (2012)
  • J. Mardaljevic et al.

    A framework for predicting the non-visual effects of daylight - Part II: the simulation model

    Light. Res. Technol.

    (2014)
  • CIE 218: 2016 - Research roadmap for healthful interior lighting...
  • P. Bodrogi et al.

    Opinion: the usefulness of light sources in human centric lighting

    Light. Res. Technol.

    (2017)
  • N. Alfonsin et al.

    Active design strategies and the evolution of the WELL Building StandardTM

    J. Phys. Activ. Health

    (2018)
  • M.G. Figueiro et al.

    Non-visual effects of light: how to use light to promote circadian entrainment and elicit alertness

    Light. Res. Technol.

    (2018)
  • M.S. Rea et al.

    Circadian photobiology: an emerging framework for lighting practice and research

    Light. Res. Technol.

    (2002)
  • Y.C. Chuang

    Spectral power distribution

  • M. Ruger et al.

    Nasal versus temporal illumination of the human retina: effects on core body temperature, melatonin, and circadian phase

    J. Biol. Rhythms

    (2005)
  • A.M. Chang et al.

    The human circadian system adapts to prior photic history

    J. Physiol.-London

    (2011)
  • Cited by (61)

    View all citing articles on Scopus

    Declarations of interest: none

    View full text