Human Lighting Research Articles

Human-centric Lighting System for the Interior of the Future

Human-centric Lighting System for the Interior of the Future

Optimization study on circadian tunability and Rec. 2020 of RGB-LED-based displays considering the users with different ages

The reasonable design of spectral power distribution (SPD) of GaN-based light-emitting diode (LED) display becomes more and more important and popular. In this work, we perform an investigation on the circadian effects of three-primary (red R, green G, and blue B, also denoted as RGB) LED based self-luminous displays (such as emerging mini-LED or micro-LED based displays) considering the users with different ages. With the increment of peoples’ ages from 1 year to 100 years, the optical transmittance of humans’ eyes may decrease due to the aging of their body functions. Therefore, it is important and meaningful for performing a spectral optimization study on the circadian effects of light that is emitting from self-luminous LED-based displays for the users with different ages. Here, the melanopic efficacy of luminous radiation (MELR) is mainly used to evaluate the circadian effects of white light coming from RGB-LED displays. With the aid of multi-objective optimization genetic algorithm (MOGA), the maximum MELR and the minimum MELR value are separately obtained for the standard observers at the age of 32, while maintaining at a certain high color gamut of Rec. 2020 standard (i.e., 60 %, 70 %, 80 %, and 90 % Rec. 2020, respectively) for these LED-based displays. Then, an extrapolation of optimal SPD at the age of 32 is done to other ages. Another parameter that can be denoted as circadian stimulus (CS) is also calculated and discussed for different ages. It is believable that this work is helpful for guiding the design and fabrication of future RGB-LED-based displays in consideration of the users with different ages, meeting large requirements of human-centric lighting (HCL) in the future.

A Path to Better Sleep and Circadian Health: Optimizing and Personalizing Indoor Lighting

Circadian rhythms play a crucial role in the regulation of sleep, metabolism, and cognitive function. However, they are highly sensitive to disturbances caused by irregular indoor lighting, especially exposure to blue light at night. This review explored the impact of indoor lighting on circadian and sleep health by analyzing trends in light exposure, socioeconomic disparities, and the prioritization of economic efficiency over health in modern lighting design. Significant variations in individual circadian rhythms present a challenge in creating standardized lighting environments. To address this issue, a review suggested the development of personalized lighting systems that use advanced sensors to monitor and respond to the circadian phase of each individual. By dynamically adjusting light intensity, wavelength, and timing, these systems can better align with personal biological clocks, promote optimal sleep and overall health, and advance the concept of truly human-centric lighting environments.

Human-Centric Lighting Design: A Framework for Supporting Healthy Circadian Rhythm Grounded in Established Knowledge in Interior Spaces

Human-Centric Lighting Design: A Framework for Supporting Healthy Circadian Rhythm Grounded in Established Knowledge in Interior Spaces

A COMPREHENSIVE REVIEW OF ENERGY-EFFICIENT LIGHTING TECHNOLOGIES AND TRENDS

Energy-efficient lighting technologies have undergone significant advancements in recent years, driving a transformation in the lighting industry. This comprehensive review explores various energy-efficient lighting technologies and trends, aiming to provide insights into their applications, benefits, and future prospects. The review begins with an overview of energy-efficient lighting technologies, including light-emitting diodes (LEDs), compact fluorescent lamps (CFLs), and advanced lighting controls. It examines the key characteristics and advantages of each technology, highlighting their energy-saving potential and environmental benefits. Next, the review discusses the trends shaping the energy-efficient lighting market, such as the transition to solid-state lighting, the emergence of smart lighting systems, and the growing emphasis on human-centric lighting design. It explores how these trends are driving innovation and transforming the way lighting is used and managed in various settings. The review also examines the benefits of energy-efficient lighting technologies, including reduced energy consumption, lower maintenance costs, and enhanced lighting quality. It discusses how these technologies contribute to energy conservation, sustainability, and improved lighting experiences for users. Furthermore, the review discusses the challenges and barriers to the widespread adoption of energy-efficient lighting technologies, such as high upfront costs, technical complexity, and the need for regulatory support. It explores strategies to overcome these challenges and accelerate the adoption of energy-efficient lighting solutions. Finally, the review provides insights into the future outlook for energy-efficient lighting technologies, highlighting emerging trends, innovative applications, and potential areas for further research and development. It emphasizes the importance of continued innovation and collaboration in driving the evolution of energy-efficient lighting technologies towards a more sustainable and efficient future. In summary, this comprehensive review offers a detailed analysis of energy-efficient lighting technologies and trends, providing valuable insights for researchers, policymakers, and industry stakeholders seeking to understand and leverage the potential of energy-efficient lighting for a sustainable future.
 Keywords: Energy-Efficient, Lighting, Technologies, Trend, Review.

The synthesis and properties of Ca3 Sc2 Si3 O12 :Ce3+ (CSSG) phosphor are utilized for the development of human-centric lighting light-emitting diodes (HCL-LEDs).

In this study, cerium ion (Ce3+ )-doped calcium scandium silicate garnet (Ca3 Sc2 Si3 O12 , abbreviated CSSG) phosphors were successfully synthesized using the sol-gel method. The crystal phase, morphology, and photoluminescence properties of the synthesized phosphors were thoroughly investigated. Under excitation by a blue light-emitting diode (LED) chip (450 nm), the CSSG phosphor displayed a wide emission spectrum spanning from green to yellow. Remarkably, the material exhibited exceptional thermal stability, with an emissivity ratio at 150°C to that at 25°C reaching approximately 85%. Additionally, the material showcased impressive optical performance when tested with a blue LED chip, including a color rendering index (CRI) exceeding 90, an R9 value surpassing 50, and a biological impact ratio (M/P) above 0.6. These noteworthy findings underscore the potential applications of CSSG as a white light-converting phosphor, particularly in the realm of human-centered lighting.

Human centric lighting luminaires: practical design

Discoveries in medicine concerning the influence of light on human physiology provoked the creation of the Human Centric Lighting (HCL) approach. Research dedicated to this mainly focuses on optimally matching light parameters to human needs, e.g. increasing concentration, relaxation, etc. However, only a properly designed light source is capable of meeting HCL goals. This paper focuses on the LED luminaire design used in HCL systems. A review of LEDs dedicated to HCL systems was performed. Their advantages and disadvantages are discussed. The Tunable White (TW) design is shown to be the most universal solution for HCL systems because it enables regulation of the colour temperature and spectrum, depending on user needs. However, TW is also the most complex in design. The problems that might arise during TW luminaire design are discussed. Example strategies on how to solve them, focusing on colour mixing and LED arrangement are given. Practical examples of TW luminaire design are also described, each one with a commentary covering encountered issues and their solutions.

A long-term stable zero-thermal-quenching blue-emitting phosphor for sustainable and human-centric lighting

In this work, we have successfully synthesized a long-term stable and highly efficient blue-emitting SMAO:Eu2+ phosphor with a double luminescence center, which does not significantly disrupt melatonin production in human-centric WLED lighting.

Insight into the optical evaluation of sunlike LED devices with full-visible spectrum emission based on ultra-low melting tin fluorophosphate glass for human centric lighting

Full spectrum sunlike light-emitting diode (LED) devices in the wavelength range of 380–670 nm have received much attention for their applications in human centric lighting. Herein, the inorganic color converter of the sunlike phosphor-in-glass (PiG) has been developed by embedding the green-emitting (Lu3-xYxAl5O12: Ce3+) and red-emitting (Sr0.6Ca0.4AlSiN3: Eu2+) phosphor powders in ultra-low melting tin fluorophosphate glass. Notably, the sunlike PiG exhibits the full spectrum in the wavelength range of 380–670 nm under the excitation of a near-ultraviolet (NUV) chip. Tunable color temperature (2785 K–5806 K) and high color rendering index (Ra = 95) were obtained by varying the mix ratio of the red-emitting component in the glass matrix. Further, the full visible spectrum emission was regulated by adjusting the Lu/Y ratio of the green phosphor Lu3-xYxAl5O12: Ce3+ and the color quality was further optimized (Ra = 97). The color quality of white light-emitting diode (WLED) was systematically investigated using Illuminating Engineering Society (IES) of North America evaluation systems and the LED devices exhibit fidelity index (Rf) and gamut index (Rg) close to sunlight (Rf = 95, Rg = 101). Compared with the traditional phosphor-in-silicone (PiS), the sunlike PiG based WLED exhibits a low working temperature of ∼37 °C for high power LED. Therefore, the WLED devices based on sunlike-PiG can be regarded as promising candidates for ultra-high color rendering index light sources because of the adjustable color temperature, high color quality, low-efficiency loss, excellent thermal properties and water stability.

Enhancing user acceptance in automated systems with human-centric lighting: the role of visual comfort, personality, and preference

Properties of light impact both psychological and physiological aspects. In this context, the effects of light’s correlated colour temperature (CCT) appear less studied than the effects of illuminance, although CCT is known to impact circadian rhythms responsible to maintain day and night cycles. Recently, Human-centric lighting (HCL) proposed to endow electric lighting with daylight dynamic characteristics with recognized benefits on physiological rhythms, particularly in reducing blue light exposure at night. Current lack of studies on the psychological effects of CCT prevents from reaching conclusions regarding the psychological aspects of HCL. The present user experiment aims to shed light on the relationship between HCL and personality, acceptance of an automated system to maximise daylight provision and visual comfort perception of occupants in two different buildings and within two types of offices. In this case, participants selected the HCL paradigm with dynamic CCT more often than a standard fixed CCT design, especially in individual offices. Despite being more frequently set and used to diffuse an appropriate light colour, dynamic CCT was assessed to deliver a heterogeneous light and decreased the overall visual comfort of occupants. Still, dynamic CCT was found to increase the acceptance of the automated system while mediating the relationship between personality and acceptance.

Melanopic photometry

Visual lighting effects have been seriously studied for more than 500 years. It was not until 2002 that physicians and biologists paid attention to the fact that the light that enters the human eye has non-visual, biological effects. Human Centric Lighting (HCL) examines the visual effects of light on human activity. Electric lighting plays a critical role in maintaining human health in today’s world, as most of us spend much of our time indoors. In 2002, a third type of photoreceptor was discovered – a nerve node cell in the retina (photosensitive, Retinal Ganglion Cell, pRGC). pRGC cells contain melatonin pigments (melanopsin) and are responsible for the spectral response of photosensitive cells. The maximum response of melatonin is achieved at a wavelength of approximately 480 nm. Fig. 1 also shows the response curves of L-, M-, and S-cones and rods based on their specific pigments. Using the response curves of L-, M-, and S-cones and rods, and having the spectra of light sources and the amount of light on the outer surface of the eye, it is possible to determine the spectrally weighted illuminances for five photopigments in the human eye. For research purposes, it is desirable to record the illuminance values for all five α illuminances. They indicate which of the photoreceptors is responding and where the light of the current lamp type is emitting. The manufacturers of light sources should be able to provide α-wave illuminances for their lamps. The International Commission on Illumination (CIE) suggested Exeltoolbox, which allows calculating these illuminances based on the spectral distribution of the lamp power. Cone-dominant metrics such as CCT (correlated colour temperature), illuminance, and luminance are not comprehensive, so melanopsin-based photosensitivity should be considered in specifications, guidelines, and during research.

The Application of Human-Centric Lighting in Response to Working from Home Post-COVID-19

COVID-19 has caused a considerable proportion of the public to work from home, either part- or full-time, in unregulated domestic conditions, which have not been designed for commercial activities. This study determined what existing lighting conditions were present in a selection of work-from-home (WFH) environments (Objective One) through quantitative lux level and equivalent melanopic lux (EML) readings by evaluating them against regulatory standards, where further study is required to validate the results with a larger dataset. This study also investigated the social demand for human-centric lighting (HCL) installations within WFH environments (Objective Two) through qualitative questionnaires by considering key parameters: sustainability, practicality, and cost. The results of Objective One showed that compliance with general safety lighting requirements was achieved by 80% of the installations. The mean lux level recorded was 452.4 lux and 0.729 uniformity, which fell below commercial requirements defined for commonly performed WFH activities; 34.3% of recorded EML dropped below the regulatory requirements under daylight conditions. When isolated to artificial lighting, only 7.5% of the required EML was achieved. The results of Objective Two showed that generally participants did not feel that their WFH installations were unsuitably lit, however, 46.2% of participants identified noticeable headaches or eye strain when working from home. A total of 80% of participants highlighted that HCL task lighting would be preferable. It was also found that participants were willing to invest in circadian lighting for health, where 63.2% of them would not accept a reduction in efficiency of over 10% compared to non HCL. Wellbeing was found to be participants’ key preference for their lighting systems, followed by efficiency, home impact, and cost.

Road Lighting Standards’ Evolution and Future Development of Smart Street Lighting Based upon Users’ Performance in View of Human Centric Lighting: A Review

This paper reviews the literature on the development of different road lighting standards or guidelines, their effectiveness as determined by motorists’ and pedestrians’ opinions in relation to human centric lighting, and another novel method to assess the impact of different lighting conditions on users’ performance using EEG and cultivating the signals from EEG. Human centric lighting, in its simplest form, is a user-dependent method, since it improves lighting sources or designs based on the findings of analyses of the visual and non-visual effects of lighting upon user performances. Human centric lighting can help users since it considers factors that can improve their mood, productivity, health, etc. By incorporating an automated smart, human centric street lighting system, this article seeks to define the fundamentals of the smart street lighting standard for Indian context. This will help save a significant amount of energy. Additionally, this paper describes a few findings and experiments that were done to determine how variations in CCTs of main and peripheral sources and flickering peripheral sources affected user reaction time and visibility level of the seen for object detection, for quantification of the parameters related to human centric lighting. It is seen in the experiments done in Jadavpur University laboratory that for high CCT values, reaction time for object detection of human observers increases, and it is also seen that flickering of light sources increases reaction time, but it does not profoundly affect the decrement of reaction time for object detection with increment of CCT value of main source.

Human-Centric Lighting Research and Policy in the Melanopsin Age.

Beyond visual function, specialized light-sensitive retinal circuits involving the photopigment melanopsin drive critical aspects of human physiology and behavior, including sleep-wake rhythms, hormone production, mood, and cognition. Fundamental discoveries of visual neurobiology dating back to the 1990s have given rise to strong interest from the lighting industry in optimizing lighting to benefit health. Consequently, evidence-based recommendations, regulations, and policies need to translate current knowledge of neurobiology into practice. Here, reviewing recent advances in understanding of NIF circuits in humans leads to proposed strategies to optimize electric lighting. Highlighted knowledge gaps must be addressed urgently, as well as the challenge of developing personalized, adaptive NIF lighting interventions accounting for complex individual differences in physiology, behavior, and environment. Finally, lighting equity issues appear in the context of marginalized groups, who have traditionally been underserved in research on both fundamental visual processes and applied lighting. Biologically optimal light is a fundamental environmental right.

Numerical correlation between non-visual metrics and brightness metrics—implications for the evaluation of indoor white lighting systems in the photopic range

From the beginning of the 21textrm{st} century until today, the demand for lighting systems includes not only visual parameters (brightness, contrast perception, color quality), but also non-visual parameters. It is necessary to define the new non-visual parameters for the realization of the new concept of Human Centric Lighting (HCL) or Integrative Lighting. As a contribution to this approach, many international research groups have tried to quantify the non-visual parameters such as Circadian Stimulus by Rea et. al. in USA (CS_{2018}, CS_{2021}), Melanopic Equivalent Daylight (D_{65}) illuminance, mEDI of the CIE S 026/E:2018 or the latest formula by Giménez et al., for the nocturnal melatonin suppression. Therefore, it is necessary to analyze the correlation between these non-visual metrics and brightness metrics such as the equivalent luminance of Fotios et al., or the latest brightness model of TU Darmstadt so that scientists, lighting engineers and lighting system users can correctly apply them in their work. In this context, this paper attempts to investigate and analyze these correlations between the three metric groups based on the database of 884 light sources of different light source technologies and daylight spectra. The obtained results show that the latest Circadian Stimulus model of Rea et. al. CS_{2021} with the improvement of Circadian Light CL_{A,2021} (CL_{A,2.0}) has solved the disadvantage of CS_{2018}, especially for the interrupted point between warm and cold white (about 3710,K) or the junction between negative and positive signal of the opponent channel (B -(L+M)). Moreover, these three metrics of the three research groups contain a high correlation coefficient, so that one metric can be transformed by linear functions to the other two parameters.

Evaluation of Lighting Quality Based On Visibility

This article discusses the issues of modelling the human centric lighting environment using computer graphics methods. Modern computer graphics programs allow for the calculation of spatial-angular distribution of luminance, a fundamental characteristic that shapes the visual perception of a scene. Richard Kelly, the founder of lighting design, states in his works that the main aspect of the comfortable visual luminous environment creating is the distribution of luminance in space. Analysing the spatial-angular distribution of luminance allows for a new stage in the evolution of assessing the quality of lighting in a simulated or real environment. By solving the task of forming a set of photometric parameters for human centric lighting (HCL) within this research, the possibility of designing a lighting installation for a specified lighting quality using computer graphics methods is demonstrated. The term human centric lighting refers to lighting that considers both the visual and non-visual effects of light on humans, starting from the visual representation of the environment and visual comfort, and extending to the impact on sleep quality, wakefulness, mood, and human behaviour. This article presents a lighting quality criterion based on spatial-angular distribution of luminance and a developed psychophysical scale, which together allow for the assessment of lighting quality using computer graphics methods.

Τhe effect of artificial lighting on both biophilic and human-centric design

The indoor environmental quality is very significant as humans spend more than 90% in indoor space. Biophilic design of indoor spaces has become a popular approach in the design of indoor building spaces sector using green walls, especially in offices, leisure and hospitality facilities. So far there exist neither guidelines with the proper Spectral Power Distribution (SPD) except for agricultural applications or intensity levels of lighting nor the proper spectral indices to transform the photopic illuminance to a new type of photometric quantity for biophilic design. On the other hand, for human centric lighting the Equivalent Melatonin Illuminance is already introduced. The aim of paper is to define the appropriate lighting conditions, not only for humans, but also for interior plants. A new metric was introduced for the biophilic design named Equivalent Photosynthetic Illuminance. The new metric was examined for two human-centric lighting luminaires and compared with the corresponding human centric lighting metrics in order to create a lighting design guide for energy-sustainable, biophilic and human-centered lighting. The different SPDs highlighted the counterbalancing impact(s) of such luminaires, between biophilic and human-centered design. The differences concerning their impact on interior lighting design were identified with regards to energy consumption, meaning that the compliance of the lighting conditions to both humans and plants results to higher energy consumption. Depending on the SPD and luminous efficacy of artificial lighting, the additional power density for proper planning of biophilic design can vary from 23.5W/m2 to 52.4W/m2 in the areas in which are applied.

Subjective Assessment of Light Environment Quality based on Human-centric Lighting

The light environment quality, in general, can be assessed from various metrics of that have been made by standard institutions such as the Indonesian National Standard (SNI), Illuminating Engineering Society (IES), or the International WELL Building Institute. However, the development of research in the field of lighting has shifted from focusing on visual quality and energy to Human-Centric Lighting (HCL). HCL requires an assessment metric to measure quality from the subjective point of view of occupants. There are two types of subjective judgments in light environment quality research, that are subjective judgments for post-experiment conditions and subjective judgments for pre & post-experiment conditions. Subjective assessment of the light environment quality based on Human-centric Lighting can be divided into three categories, that are visual, emotional and biological assessments. For the subjective assessment instrument of the visual category, researchers can use the glare sensation assessment standard. Meanwhile, for the assessment of the light environment quality from the emotional category, there is no specific standard. And for assessing the light environment quality from the biological category, researchers can use commonly used assessment standards, such as the Karolinska Sleepiness Scale (KSS), Pittsburgh Sleep Quality Index (PSQI), and Epworth Sleepiness Scale (ESS). For an assessment category that does not have a standard, the researcher can arrange a research instrument from the results of the literature review and adapt it to the conditions of the research study object.

Climate-responsive machine learning-based control of switchable glazing towards human-centric lighting

This work presents a climate-responsive control of switchable glazing using machine learning models. Here carried out experimental investigations in daylight artificial light integrated room on Polymer-dispersed liquid crystals (PDLCs) for collecting data towards modelling. A support vector machine learning classification algorithm is designed to model the transparency change in PDLC. A tunable LED luminaire is used to adjust the brightness and circadian effectiveness in the test room. The real-time implementation of the model gives the states of switchable glazing under various climate conditions. Real-time experimentation is carried out to verify the results. It is observed that the Interior light colour characteristics were satisfactory under different PDLC states. Correlated colour temperature (CCT) and circadian stimulus (CS) were similar to daylight. In the available literature, simulation results show PDLC as satisfactory for visual comfort. However, the experimental investigations and the prediction models give a range of sunlight on the window and solar altitude for which it satisfactorily works; outside this range, PDLC acts as a luminous source. The feasibility of PDLC in all window orientations is also simulated. The Simulink model can give the states of switchable glazing by optimising visual comfort, thermal comfort and energy effectiveness.

Evaluation of Occupants’ Visual Perception in Day Lit Scenes: A Virtual Reality Experiment

Daylight improves indoor environmental quality, the physical and mental health of occupants, and their efficiency. Research in the area of human-centric lighting that considers the visual and non-visual effects of light on human vision, have focused on examining human visual perception in response to a wide variety of lighting aspects. To investigate the effect of surface materials, window size, and shading patterns on participants’ evaluation of brightness, daylight distribution, contrast, and satisfaction with view, a virtual reality experiment is implemented in a university classroom. Moreover, responses are compared with metrics (i.e., RAMMG and illumines level) to evaluate their performance and robustness. Thirty-three subjects evaluated thirteen immersive virtual environments (IVEs) with different glazing visible light transmittance, reflectance coefficient of surfaces, window to wall ratio, number of windows, and shading geometry using a Likert-type scale survey. The results indicated that participants’ evaluation of brightness is influenced by reflection coefficient of the surfaces and WWR. While daylight distribution is affected by number of windows and shading geometry in addition to other studied parameters. Based on the subjects’ responses the contrast is only affected by reflection coefficient of the surfaces. Their satisfaction with amount of outside view is also influenced by WWR and number of windows. Moreover, based on statistical results defining a specific range of acceptable contrast based on the RAMMG metric is not suggested, and users' evaluation depends on the surface material in addition to the reflection coefficient of them. Furthermore, the level of lighting perceived by people is affected by materials and their color (beside the reflection coefficient of the surfaces), number of windows (even with similar WWR), and shading pattern (even with the same aperture ratio) as well as the glazing visible light transmittance.