Indoor Lighting Research Articles

Exploring Asymmetric Lens–Total Internal Reflection (AL–TIR) Optics for Uniform Ceiling Illumination in Interior Lighting

This study presents a significant advancement in LED interior lighting through the development and application of Asymmetric Lens–Total Internal Reflection (AL–TIR) optics, with a focus on enhancing lighting uniformity and indoor comfort by simulating sky-like lighting distribution. AL–TIR technology employs asymmetric lenses combined with total internal reflection to efficiently redirect and spread light, achieving a controlled and even ceiling illumination suitable for various interior applications. This research explored the establishment of ideal luminous intensity curves, devised practical AL–TIR optical designs through numerical calculations, and conducted extensive simulations to assess performance in typical indoor environments. Our findings demonstrated substantial improvements in lighting uniformity, with the AL and AL–TIR systems achieving direct illuminance uniformities of 0.78 and 0.83, respectively, compared to traditional tube LEDs at 0.25. These results, validated in several office rooms, highlight the efficacy of AL–TIR optics in revolutionizing indoor lighting design by balancing optimal lighting distribution with occupant comfort and well-being.

Experimental Evaluation Study of the Comfort and Energy Performance of Suspended Particle Device Smart Windows in a Residential Building: Achieving Optimal Control during the Cooling Season

In contrast to traditional windows, smart windows dynamically affect indoor visual and thermal environments through Visible light transmittance (VT) and Solar heat gain coefficient (SHGC) changes. Therefore, for enhancing smart window application effects, it is necessary to analyze comprehensively the impacts of smart window tinting on indoor visual and thermal environments, and to establish appropriate tinting control methods. This study aimed to determine optimal smart window control strategies for residential buildings during the cooling season by evaluating visual and thermal comfort and energy performance in an actual building equipped with SPD smart windows. An experimental building was located in Sejong, South Korea (36.5°N latitude, 127.3°E longitude; temperate climate zone), and the measurements were conducted from July to August 2023 to compare glare, indoor daylight illuminance, thermal comfort, and cooling and lighting energy between typical and smart windows. And, optimal control methods were proposed from general comfort and energy performance perspectives. The measurements indicated that it was difficult to satisfy all aspects of the visual and thermal environment, and comprehensively it was recommended to employing “always tinting” on summer. However, on a clear day, jointly applying smart windows and lighting dimming control and controlling automatically based on indoor daylight illuminance levels were found to be the most effective as it not only secured visual comfort performance but also reduced lighting energy consumption.

Wide Bandgap Donor can Offer High‐Efficiency LED Indoor Organic Photovoltaic with Indium‐Doped Zinc Oxide Electron Transport Layer

Indoor organic photovoltaic (OPV) cells offer a compelling solution for powering diverse electronic devices integrated into the Internet of Things (IoT) network. They are prized for their robust power conversion efficiency (PCE), mechanical resilience, and ultra‐thin nature. The recent surge in inverted‐structure OPVs reflects their enhanced stability over conventional designs. Despite the advantage, their adaptation for indoor light utilization remains underexplored. Optimal selection of an electron transport layer (ETL) with precise energy band alignment is critical in this system. Herein, an inverted‐structured OPV is fabricated utilizing PBDB‐T as the wide bandgap donor, with a focus on enhancing its PCE under 1000 lx LED illumination through the doping of the zinc oxide‐ (ZnO‐) based ETL with indium (In). The results indicate that the device utilizing undoped ZnO as the ETL achieves a peak PCE of 9.42% under these specified conditions. Conversely, the OPV utilizing In‐doped ZnO as the ETL achieves a significantly higher PCE of 29.78% with 5 at% In, indicates the usefulness of ETL doping by In. This may be caused by the tuning of energy band alignment, improvement in electron mobility, and reduction in surface roughness of ZnO by In doping.

Relationship between indoor environmental quality and guests’ comfort and satisfaction at green hotels: A comprehensive review

Abstract Recent studies have focused on different aspects of green management, practices, and green consumption in the hotel industry. However, there is a need to explore and better understand the association between indoor environmental quality (IEQ) and green hotel guest’s comfort. Therefore, it is essential to explore the effects of IEQ on the comfort and satisfaction of green hotel guests. This study conducts a comprehensive review of the effects of various IEQ parameters, including indoor air quality, thermal comfort, lighting, visual/view, acoustic comfort, building characteristics, decoration, and indoor greenery, on guest’s comfort and satisfaction in green hotels. Based on previous literature, it was also revealed that most current green building schemes lack of comprehensive evaluation of the performance of IEQ dimensions in green hotels. It was also observed that these IEQ parameters show a significant influence on the hotel guest’s comfort and satisfaction. Based on the findings of the literature review, a conceptual model was developed to represent the relationship between the IEQ parameters and guest’s comfort and satisfaction. The proposed conceptual model can be implemented by the hotel management for a comprehensive assessment of guests’ perceptions toward the IEQ in green hotels. The novelty of this study is based on its findings that establish a more effective IEQ evaluation method and serve as the reference scenario of IEQ, which can be a useful tool for both academician and practitioners and contribute to improving the indoor environmental performance of green hotels through highlighting the key IEQ parameters, which affect the comfort and satisfaction of hotel guests.

Modeling impacts of indoor environmental variables on secondary organic aerosol formation

There are numerous air pollutants indoors including chemicals emitted from building environments as well as outdoor-origin species due to human activities. Despite the significance of indoor air quality, the atmospheric process indoors is not well studied. In this study, the secondary organic aerosol (SOA) formation from the oxidation of α-pinene blended with toluene was simulated under varying indoor environments (lamps, NO2, ozone, and inorganic seed) using the UNIfied Partitioning Aerosol Reaction (UNIPAR) model. Explicitly predicted lumping species produced during the atmospheric oxidation of precursors are used in the model and they process multiphase partitioning and aerosol phase reactions. The performance of the model was demonstrated using indoor chamber experiments in both dark conditions (ozonolysis) and light conditions with commercialized fluorescent or LED lamps. α-Pinene SOA was dominated by ozonolysis even in the presence of indoor light. Toluene, which is known to be photochemically processed, was oxidized in the dark condition with OH radicals that were derived from ozonolysis products of α-pinene. At given dark simulation conditions (10 ppb α-pinene, 30 ppb ozone, and 50 ppb of toluene), toluene contributed 15 % of SOA mass. α-Pinene SOA was insensitive to hygroscopicity of inorganic seed, but toluene blended with α-pinene increased the sensitivity to seed conditions due to the formation of oligomeric matter via aqueous reactions of reactive toluene products. In the presence of NO2. α-pinene SOA formation significantly increased with increasing NO2 owing to the reaction of α-pinene with nitrate radicals to form low volatile products. This study concludes that ozone and NO2, intruded from outdoors to indoors, effectively oxidize terpenes and furthermore aromatic hydrocarbons with OH radicals originating from ozonolysis of terpenes. The reaction paths with ozone and nitrate radicals are more effective at forming SOA than that with OH radical under the indoor light condition with commercialized lamps.

The Non-Image-Forming Effects of Daylight: An Analysis for Design Practice Purposes

Daylight plays a crucial role in human health, and as research into its effects expands, it is essential for designers to estimate the non-image-forming impacts of various daylighting and lighting strategies. This allows them to create indoor environments that are both pleasant and comfortable. To support this, daylight measurements were taken in five Chinese cities, focusing on spectral power distribution, correlated color temperature, and illuminance. The study calculated the non-image-forming effects of daylight exposure using metrics like melanopic Equivalent Daylight Illuminance and Circadian Light. A key finding was the development of the action factor SAI, which estimates the potential non-image-forming effects of light in built environments. This factor serves as a proxy for understanding how non-image-forming effects relate to correlated color temperatures. Additionally, the research suggests the possibility of creating a time-variational daylighting and lighting strategy with four distinct periods of non-image-forming effects throughout a 24 h day. These insights could be valuable for architects and designers in optimizing indoor lighting systems.

Unveiling the potential of Cs2AgBiBr6 perovskites for next-generation see-through photovoltaics

Lead-free perovskite solar cells are strong contenders in the race for green and sustainable energy. Among these, cesium silver bismuth bromide (Cs2AgBiBr6) stands out, but its potential was hampered by the need for high-temperature processing, hindering its transition to scalable techniques. In this work, we present the feasibility of blade-coating deposition of Cs2AgBiBr6 layer. Thanks to the temperature control of the substrate during the process, we deposited uniform films at precise thickness enabling the fabrication of fully semitransparent devices with power conversion efficiencies (PCEs) of 3.07 % and 7.7 % under 1 sun and indoor light conditions, respectively. Furthermore, we evaluated important metrics for transparent photovoltaics such as Light Utilization Efficiency (LUE) and Color Rendering Index (CRI) of the devices by varying the Cs2AgBiBr6 thicknesses and the illumination conditions. The results showed LUEs at 1 Sun illumination of 1.1 % (1.5 %) and CRI of 71 (62.5) for 200 nm-thick and 400 nm-thick perovskite films, respectively. Finally, we evaluated the process scalability fabricating 6 cm2-sized semitransparent modules suitable for low-power electronics in Internet of Things field. This study opens the door to the development of non-hazardous, scalable, lead-free perovskite solar cells and modules suitable for integration into our everyday surroundings thanks to their see-through properties.

Investigating the effects of indoor lighting on measures of brain health in older adults: protocol for a cross-over randomized controlled trial

BackgroundThe worldwide number of adults aged 60 years and older is expected to double from 1 billion in 2019 to 2.1 billion by 2050. As the population lives longer, the rising incidence of chronic diseases, cognitive disorders, and behavioral health issues threaten older adults’ health span. Exercising, getting sufficient sleep, and staying mentally and socially active can improve quality of life, increase independence, and potentially lower the risk for Alzheimer’s disease or other dementias. Nonpharmacological approaches might help promote such behaviors. Indoor lighting may impact sleep quality, physical activity, and cognitive function. Dynamically changing indoor lighting brightness and color throughout the day has positive effects on sleep, cognitive function, and physical activity of its occupants. The aim of this study is to investigate how different indoor lighting conditions affect such health measures to promote healthier aging.MethodsThis protocol is a randomized, cross-over, single-site trial followed by an exploratory third intervention. Up to 70 older adults in independent living residences at a senior living facility will be recruited. During this 16-week study, participants will experience three lighting conditions. Two cohorts will first experience a static and a dynamic lighting condition in a cluster-randomized cross-over design. The static condition lighting will have fixed brightness and color to match lighting typically provided in the facility. For the dynamic condition, brightness and color will change throughout the day with increased brightness in the morning. After the cross-over, both cohorts will experience another dynamic lighting condition with increased morning brightness to determine if there is a saturation effect between light exposure and health-related measures. Light intake, sleep quality, and physical activity will be measured using wearable devices. Sleep, cognitive function, mood, and social engagement will be assessed using surveys and cognitive assessments.DiscussionWe hypothesize participants will have better sleep quality and greater physical activity during the dynamic lighting compared to the static lighting condition. Additionally, we hypothesize there is a maximal threshold at which health-outcomes improve based on light exposure. Study findings may identify optimal indoor lighting solutions to promote healthy aging for older adults.Trial registrationClinicalTrials.gov Identifier: NCT05978934.

Environmental Impacts on the RSS-Based Visible Light Indoor Positioning System

To address the shortcomings of the global positioning system (GPS) operating within indoor scenarios, a range of indoor positioning systems (IPS) have been proposed. Among these, visible light IPS garners substantial research interest for its potential as a cost-effective IPS solution. However, susceptibility to environmental influences like external light and non-line-of-sight that can significantly affect its performance hindered its adoption. Hence, a simulation framework capable of simulating these influences becomes crucial in supporting the effective deployment and promoting the adoption of visible light IPS. This paper investigates the feasibility of using a simulation framework to replicate environmental factors affecting the system, including external optical sources and blocked transmitters. The research involved the development of a received signal strength (RSS) based visible light IPS prototype and an associated simulation framework. Subsequently, the prototype was tested in three distinct environments: no influences, with an external optical source, and non-line-of-sight. The prototype achieved an accuracy of 0.0836 m, 0.3541 m, and 1.1519 m for 50% of the time respectively in these three environments. Ultimately, the simulation framework developed is capable of reproducing similar effects for all three environments with a difference in the accuracy of 76.08%, 74.86% and 867%, respectively. Thus, the findings support the use of the developed simulation framework for the effective development of visible light IPS in environments with no influences and with external optical sources.

Dimerized Non-Fullerene Acceptor-based organic photovoltaics for Round-the-Clock functioning

Organic photovoltaics (OPVs) have emerged as a key sustainable energy technology capable of efficiently generating electricity from both direct sunlight and low-intensity indoor lighting. Despite ongoing research to improve their performance, limited efforts have been undertaken to develop OPVs that can operate consistently (24/7/365) under versatile lighting conditions. For effective utilization, OPVs must demonstrate efficient operation under both outdoor and indoor illumination conditions, generating sufficient electrical power to drive microelectronic devices. Low-bandgap non-fullerene acceptors (NFAs) in OPVs are limited by low open-circuit voltage (VOC) under indoor lighting, restricting their performance. While high-bandgap NFAs can improve indoor power-conversion efficiency (PCE) by elevating VOC, they may often reduce outdoor performance owing to reduced light harvesting. Thus, we developed OPVs using the oligomeric dimerized NFA DYBO, which simultaneously achieved an excellent PCE of 16.7 % under simulated solar illumination and a remarkable maximum power output density (Pmax) of 0.079 and 0.396 mW/cm2 under a 5,200 K LED and halogen lamp (1000 lx), respectively, attributed to elevated VOC and reduced short-circuit current density (JSC) losses. The optimized OPVs demonstrated PCEs nearly equivalent to those of the current state-of-the-art under indoor illumination, with a remarkable Pmax capable of autonomously powering a variety of microelectronic devices.

Application of low energy building thermal energy optimization based on image recognition and light sensors in urban green environment planning

The paper analyzes the application of thermal energy optimization scheme based on image recognition and light sensor technology in low-energy buildings, in order to improve building energy efficiency, reduce energy consumption and provide scientific basis for urban green environment planning. In this paper, image recognition technology is used to monitor the light change in the external environment of the building, and the indoor light intensity data is obtained by the light sensor in real time. Combined with big data analysis, building heat optimization model is established, intelligent control system is designed, and the heating and cooling system of the building is dynamically adjusted, so as to achieve efficient use of heat energy. The experimental results show that the thermal energy optimization method based on image recognition and light sensor has a good application prospect in low-energy buildings, which not only effectively reduces energy consumption, but also contributes to the sustainable development of urban green environment.

Dynamic facade potential for indoor lighting uniformity

Abstract The facade is an important part of a building. Its existence affects the comfort of the users. the situation outside the building is often unfavorable for the users, so the facade must be reliable as a protective element. the tropical climate receives an abundance of sunlight throughout the year. its rays can be used for natural lighting. But the rays also carry heat, which makes it uncomfortable. the entry of sunlight can be controlled. one possibility is to make the facade elements move following the sun’s movement. The aim of this research is to compare the performance of static and dynamic facades in terms of the uniformity of light entering the room. The value of lighting uniformity in condition 1 has a relatively small. This is due to the high intensity of light entering the room without obstruction resulting in high contrast Condition 2 uses a static facade. The value obtained is higher in comparison with condition 1. This is due to the presence of a shade that makes the light contrast not occur too large. Condition 3 uses a shade that rotates with the sun movement every hour. The comparison value tends to decrease but, when viewed, the value of the decrease is not as fast as condition 2. Judging from the three facade conditions, condition 3, namely the dynamic facade, has the smallest decrease in lighting uniformity. This demonstrated that the longest lighting uniformity occurs in condition 3

Three-dimensional visible light positioning through fisheye camera

Abstract Visible light can be utilized to achieve indoor high-precision positioning. However, most visible light positioning (VLP) systems only achieve two-dimensional (2D) positioning and require a dense LED layout as the transmitter. Therefore, we propose a novel three-dimensional (3D) visible light indoor positioning system, which uses the fisheye camera as the receiver, designs an LED width comparison method to reduce the requirement of LED density, and realizes 3D positioning. When images captured by the fisheye camera distort, we use the checkerboard calibration method to correct the distortion parameters of the fisheye camera. The parameters can be used to improve the impact of image distortion on the positioning effect. For the LED width comparison method, we set up a discrete height-width database, fit a curve between height and LED width, and calculate the receiver height according to the linear relationship. Extensive results show that the positioning system can achieve a 3D positioning with 9.66cm average error.

Construction of a Model for Assessing the Comfort of Residential Indoor Environment Based on Multisensory Design

Economic development and technological progress have made people’s demand for indoor environments higher and higher, and designing safe, comfortable, and healthy indoor environments through multisensory design is worthy of serious consideration. In order to realize the assessment of indoor environment comfort under multi-sensory design, this paper carries out data assessment from three dimensions of thermal environment, light environment and air environment. Relying on the PMV model of thermal environment comfort, we analyze the trends of indoor temperature and humidity, average radiant temperature, and PMV values. Combine Weber-Fechler and lighting coefficient to study the visual comfort change of indoor light environment, and analyze the lighting illuminance of indoor light environment under different working conditions by illuminance uniformity. From the basic principle of indoor wind environment, the changes of effective temperature difference and blowing sense caused by air temperature and wind speed are investigated. The temperature difference of the south-facing room decreased between 12.14% and 15.65% before and after the heating was stopped, which is a small change. The average indoor ambient radiant temperature values at different measurement points were up to 27.59 °C, and the fluctuations of the average indoor thermal ambient PMV values were within the range of [-1.2,1.6]. When the indoor light ambient illuminance value increased from 200 lux to 600 lux, the visual comfort improvement was more significant than from 600 lux to 1000 lux. The indoor air distribution characteristic ADPI value was 100% when the air velocity was 0.15m/s and 0.25m/s. Based on the results of indoor environment comfort assessment, multisensory optimization of indoor environment comfort from heat, light and air environments is proposed to provide guidance for improving people’s satisfaction with indoor environment.

Optimizing Classroom Lighting: Balancing Illuminance Uniformity and Glare Control with Led Technology

Indoor lighting environment significantly impacts students’ concentration and learning performance. Optimal lighting conditions enhance reading speed, accuracy, and comprehension abilities. In contrast, poor lighting conditions may lead to decreased concentration and increased errors in tasks. Therefore, classroom lighting is an important factor to consider in classroom design to optimize cognitive efficiency of students. Current classroom lighting solutions using LED systems have met European Norm (EN) standard in terms of illuminance and energy efficiency. However, although the issue of glare has been addressed, it has not been completely resolved. This study introduces a solution for glare-free classroom lighting that maintains uniformity while adhering to existing standards. This approach aims to create a visually comfortable learning environment, balancing effective lighting with glare reduction.

Three-dimensional evaluation of the responses of two species of flies (Diptera) to an indoor light trap

Abstract We used the Photonic Fence Monitoring Device (PFMD) to evaluate orientation by Musca domestica L. (Diptera: Muscidae), and Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) to the Zevo Flying Insect Trap Model 3. The PFMD’s dual cameras record infrared light (IR) reflected from a wavelength-specific fabric; insects do not reflect IR at the same wavelength and are tracked in 3 dimensions as moving objects. The plug-in trap emits ultraviolet and blue light from behind an opaque shield; attracted insects enter the space between the shield and the wall and are trapped on a sticky cartridge facing the wall. An experiment (N = 10) with replicates of approximately 40, 1- to 7-day-old mixed-sex flies of each species was conducted in a 6.1 m3 arena. Prior to turning the trap on, the fly movement was not directed toward the trap on the back wall of the arena, regardless of whether the overhead light was on or off. When the overhead light was off, the mean first catch of both species occurred within 5 min after the trap was turned on, and 33.1% and 41.8% of M. domestica and C. vicina, respectively, were caught. House flies flew toward the trap, many approaching from below, while C. vicina apparently walked or flew outside the field of view of the PFMD until they appeared on the vertical reflective surface, and then walked toward the trap from all directions. Our results show that the Zevo Trap attracts and catches flies, and that the PFMD can be used to track flying and walking flies.

Research on the health lighting scheme of university library reading room

The quality of the indoor lighting environment in the reading space of the university library is essential for students' visual perception, emotional evaluation, and cognitive efficiency. The design of the lighting environment considering the change of natural light is one of the important development directions to improve the light environment quality of the reading room and meet the health requirements of students. This paper from the perspective of reading vision, emotion, and cognitive probes into the natural light environment lighting design, builds a reading lighting environment laboratory, using subjective evaluation, task performance, and physiological indicators of the measurement method, first analyses the weight of different indicators under different time, establish lighting environment comprehensive evaluation index I and artificial illumination and desktop illumination prediction model. The experimental results show that experimental results show that visual discomfort and clarity are the key factors in the early and later stages. In the transition phase, emotional indicators become particularly important. The model of dynamic lighting design scheme during 17:30–20:30 is: y = 227753.1746–900120.63492x+ 1179428.57142x2-512000x3, R2 = 0.99702; the fitting formula of desktop illumination in 17:30–20:30 period is: y = 566.666667–197.08995x + 158.73016x2-37.03704x3, R2 = 0.95238. The results aim to provide a theoretical basis for the design and optimization of dynamic lighting under natural light in the library reading room.

The use of UV-A radiation for biofortification of lettuce and basil plants with antioxidant phenolic and flavonoid compounds

Stable plant production is a crucial concern of modern agriculture facing increasing food demands and the risk of less predictable weather conditions in the open field. Alternative approaches for plant production are greenhouses and indoor farming. Modern LED-based artificial lighting indoor facilities allow not only to fill the gap in the supply chain of food production, but to produce plants characterized with higher concentration of essential phytochemicals. Thus, in this study, we attempt to analyse the efficiency of short-term supplementation of spectrum within ultraviolet A light (UV-A, 365 nm) to increase the antioxidant potential of leafy plants, assessed by total phenolic (TPC) and flavonoid (TFC) content. To this end, two distinct cultivars of baby leaf lettuce (Lactuca sativa var. crispa L.) and microgreens basil (Ocimum basilicum L.) plants were grown under red-green-blue spectrum supplemented prior to harvest with low doses of UV-A radiation. Analyses showed that UV-A exposition enhanced TPC and TFC with green leaf cultivars, compared to dark-pigmented ones. The analysis also proved that plants exposed to UV-A presented higher overall antioxidant potential measured with 1,1-diphenyl-2-picrylhydrazil (DPPH). Results are crucial for better understanding the potential of UV-A supplementation to produce functional plants which are natural sources of dietary antioxidants.

Retraction Note: Application of indoor light sensor based on monitoring image recognition in basketball sports image analysis and simulation

Retraction Note: Application of indoor light sensor based on monitoring image recognition in basketball sports image analysis and simulation

Optical characteristics, Judd-Ofelt analysis of enhanced luminescence by flux in thermally stable, novel Eu3+- doped BaZr(PO4)2 phosphor for indoor lighting applications

A series of novel single phased Eu3+ doped BaZr(PO4)2 phosphor were synthesized employing simple solid-state reaction route and studied the influence of different chlorides as fluxes (NH4Cl, KCl, LiCl and NaCl) on structural and photoluminescence properties. The structural characterization reveals pure phase formation of the as prepared phosphors with monoclinic crystal structure. The photoluminescence (PL) spectra recorded under 392 nm excitation depicts intense emission at 612 nm. Further, the concentration of Eu3+ ion was well tuned by carefully studying the PL spectra and the optimised amount of Eu3+ ion in BaZr(PO4)2 is found to be 3.0 mol%. The luminescence properties of phosphor with added aforementioned fluxes were also studied in detail. NH4Cl was found to be the best among all the fluxes taken and the photoluminescence intensity of phosphor gets enhanced by 1.43 times of without flux. The Judd-Ofelt theory was employed for determination of spectral parameters from photoluminescent emission spectra. The temperature dependent photoluminescent studies establishes stability of phosphor emission at operating temperatures. The CIE coordinates were evaluated that confirms the pure red emission under n-UV excitation. All the studies indicate the potential of the said phosphor in phosphor converted white light emitting diodes as red emitter and indoor lighting.