Daylight Modelling Research Articles

Hyperspectral environmental illumination maps: characterizing directional spectral variation in natural environments.

Objects placed in real-world scenes receive incident light from every direction, and the spectral content of this light may vary from one direction to another. In computer graphics, environmental illumination is approximated using maps that specify illumination at a point as a function of incident angle. However, to-date, existing public databases of environmental illumination specify only three colour channels (RGB). We have captured a new set of 12 environmental illumination maps (eight outdoor scenes; four indoor scenes) using a hyperspectral imaging system with 33 spectral channels. The data reveal a striking directional variation of spectral distribution of lighting in natural environments. We discuss limitations of using daylight models to describe natural environmental illumination.

Evaluation of climate-based daylighting techniques for complex fenestration and shading systems

The latest advancements in glazing technology are driving facade design towards complex and adaptive fenestration systems. Accurate simulation of their optical properties and operational controls for building daylight performance evaluation requires advanced modelling techniques, such as climate-based daylight modelling (CBDM). At the same time, computational efficiency is key to quickly simulate this complex performance over a full year. Over the years, several CBDM techniques were developed to answer these two main challenges, but they were never systematically benchmarked against each other. This paper compares state-of-the-art Radiance-based simulation techniques in terms of annual daylight performance metrics required by national guidelines and international green building rating schemes. The comparison is performed on three different shading systems: diffuse Venetian blinds, specular Venetian blinds, and perforated solar screens. Findings show that simulation methods are characterised by significant differences in their implementation and visual rendering, but most annual daylight metrics result in consistent values (within ± 20%). A notable exception is Annual Sunlight Exposure, which is highly sensitive to the chosen simulation method, with differences of up to 47 percentage points. Additional outcomes from the present work are used to compile a list of generalised recommendations for designers and policy makers.

A circadian design assist tool to evaluate daylight access in buildings for human biological lighting needs

This paper reports on the development of a simulation-based Design Assist Tool capable of assessing the circadian performance of architectural daylighting strategies during the design process. The tool integrates GIS site data, parametric modeling of multi-level building forms and multi-spectral lighting simulation of biological lighting effects into a Climate Based Daylight Modelling (CBDM) workflow capable of automatically performing hourly (or sub-hourly) time-series evaluations over selected days throughout the year. Outputs of the tool can be used to visually and quantitatively assess the extent to which a prospective daylighting design complies with emerging circadian lighting requirements over an annual period using daylight. An example application of the Design Assist Tool is presented to differentiate performance of varying building forms located on an urban site in Downtown Los Angeles.

Photon mapping in image-based visual comfort assessments with BSDF models of high resolution

Data-driven models replicate the irregular Bidirectional Scattering Distribution Functions (BSDFs) of optically Complex Fenestration Systems in daylight simulation. RADIANCE employs the tensor tree to store the BSDF at high directional resolution. Its application in backward ray-tracing is however challenging, since the density of stochastic samples must match the model resolution. BSDF proxy and peak extraction address this problem, but are limited to cases when either the fenestration geometry, or the shape and direction of the transmission peak are known. Photon Mapping is proposed to efficiently sample arbitrary BSDFs from the known sun direction. The existing implementation in RADIANCE is extended to account for light sources and their reflections in the field of view, that are of particular importance for visual comfort assessments. The method achieves a high degree of accordance with ray-tracing, and reduces simulation times by ≈95% with data-driven models of high resolution.Abbreviations: BRT: Backward Ray-Tracing; BSDF: Bidirectional Scattering Distribution Function; CBDM: Climate-Based Daylight Modelling; CFS: Complex Fenestration System; DGI: Daylight Glare Index; DGP: Daylight Glare Probability; FPM: Five Phase Method; GPGPU: General Purpose Graphics Processing Unit; LCP: Laser Cut Panel; OoC: Out-of-Core; PM: Photon Mapping; RMSE: Root Mean Squared Error

Analytical Prediction of Tubular Light-Pipe Performance Under Arbitrary Sky Conditions

The tubular light guides are devices allowing deliverance of solar light into deep interior rooms, offices, or underground spaces. Due to considerable costs of such systems, the reasonable assessment of their lighting performance is desirable. To predict accurately their efficiency, precise numerical computations have to be performed. Such computations may be strongly time consuming, mainly when mass calculations are required as it is in case of the so-called climate-based daylight modeling. This paper presents an analytical solution to the optical efficiency of cylindrical straight pipes that is applicable over a wide range of pipe’s parameters and under arbitrary sky luminance conditions. The proposed method gives results in good agreement with ray-tracing numerical simulations—the mean absolute percentage errors are less than 3%—but unlike them, the calculations are much faster. Therefore, it appears to be convenient for daylight modeling, which takes into account utilization of tubular light guide systems in buildings.

Climate-Based Daylight Modelling for compliance verification: Benchmarking multiple state-of-the-art methods

Climate-Based Daylight Modelling (CBDM) gives designers the possibility to evaluate complex, long-term luminous environment dynamics. This complexity can be challenging to simulate, and even more challenging to communicate effectively through the use of performance metrics. A multiplicity of CBDM techniques and metrics has been developed over the last two decades, but these were rarely assessed against each other. This paper reviews four state-of-the-art techniques based on the Radiance raytracing engine and systematically compares them against a benchmark CBDM method. Four classroom spaces are used to carry out an inter-model comparison between performance metrics commonly used for compliance verification obtained from all analysed techniques. Additional sensitivity analyses assessed how changes in input variables influence such metrics.Results from the inter-model comparison showed that the representation of direct sunlight is markedly different between the various CBDM techniques, and that metrics based on horizontal direct sunlight are very sensitive to the choice of simulation method. This led to differences in predicted Annual Sunlight Exposure up to 39 percentage points. Metrics that consider both direct and inter-reflected light were found to be more robust, with variations from benchmark results within ±15%. The analysis of the input variables showed that sensor grid spacing and time-step interpolation do not significantly affect any of these metrics. Changes in orientation and sky discretisation scheme had different effects depending on the metric and technique considered. The need for authoritative benchmarking systems when introducing new performance metrics for compliance verification or new simulation methods is also discussed.

Dynamic evaluation of daylight availability in a highly-dense Chinese residential area with a cold climate

Daylight utilization in urban areas is receiving increasing attention from urban planners and developers, architects and engineers. This study investigated the daylighting availability within buildings of a highly dense residential urban area under a cold climate in north-east China. Based on innovative simulations using climate-based daylight modelling (CBDM), three typical urban layouts have been assessed according to vertical daylight illuminance at the building facade. A comprehensive analysis of daylighting potential has been completed through various approaches including typical time (9 a.m., 12 p.m. and 3 p.m.), yearly average daylight illuminance and a proposed external daylight metric based on the frequency. Several interesting relationships are found between daylighting potential, urban forms, and climate conditions. A number of design strategies and guidelines are produced to support early stage urban planning and design.

Safety effects of street lighting on roadway segments: Development of a crash modification function

Objective: Nighttime crashes are overrepresented on the U.S. highway system. Roadway lighting, which provides additional visibility by supplementing vehicle headlights, has been identified as an effective countermeasure to improve nighttime safety. However, the existing literature does not provide a thorough understanding of the effects of street lighting photometric characteristics on nighttime crash occurrence on roadway segments. This study aimed to investigate the relationship between lighting photometric measures and nighttime crash risk on roadway segments and develop a crash modification function/factor (CMF).Methods: The research team collected horizontal illuminance data on 440 roadway segments between 2 successive signalized intersections in Florida for 2012–2014 and matched 4 years of nighttime and daylight crash data (2011–2014). Random parameter negative binomial models were estimated for both nighttime and daylight crash frequencies. The expected night-to-day crash odds ratio, as an equivalent of CMF, was derived from the fitted models with the correction of estimation variances. The confidence intervals (CIs) of the developed CMF were estimated using the Cox method.Results: The coefficient of the mean of horizontal illuminance is significantly negative in the nighttime model. The coefficients of the standard deviation of horizontal illuminance are significantly positive and normally distributed in both the nighttime and daylight models. The significance of the standard deviation in the daylight model captures the confounding effects—a high standard deviation correlates with high traffic exposures, poor safety design standards, and low maintenance quality. The CMF based on the expected daylight-to-day odds ratio was developed as an exponential function of the increments and the increment squares of the mean and the standard deviation of horizontal illuminance. Its 95% CIs indicate that the CMF is almost significant over the whole range. Other significant variables contributing to nighttime crash risk include annual average daily traffic, truck percentage, segment length, access density, undivided roads, and urban/city limits.Conclusions: Horizontal illuminance characteristics have a significant impact on nighttime crash risk on roadway segments. An increase in the mean of horizontal illuminance, indicating an improvement in average lighting level, tends to decrease nighttime crash risk; an increase in the standard deviation, representing a poor uniformity of lighting pattern on a roadway segment, is more likely to raise nighttime crash risk. Because the 2 measures are strongly correlated in a low mean range (<0.44 fc), the 2 photometric measures need to be considered together to interpret the safety effects of lighting patterns. The standard deviation shows better performance in measuring lighting uniformity on a roadway segment than the traditional ratios (max-to-min and mean-to-min). However, a new photometric measure is needed to capture the true lighting pattern influencing driver vision at night.

Investigating Night Flushing Potential in a Multi-Storey, Open-Plan Office in Germany Using TRNLizard with TRNSYS 18

Despite growing interest in sustainable office buildings and technological advancements, often either comfort or energy is sacrificed at the expense of the other in the conventional approach. Designers and architects tend to lean towards fully glazed buildings in a multi-floor office building due to its light structure, transparency and more access to daylight compared to traditional buildings. However, their energy efficiency and impact on occupant comfort – thermal, glare and visual – are questioned. Some practitioners, therefore, prefer a fully sealed façade with a low glazing ratio to reduce energy consumption. This paper argues that wellness and energy savings are not contradictory aspects of design. It is shown that measures to create an exceptional, healthy environment for occupants drive conservation and energy efficiency. Such design needs special considerations at the early stages that significantly affect decisions regarding passive strategies. To help drive first decisions, an accurate and fast simulation tool that considers dynamic thermal, daylight and airflow models is required. However, some passive measures such as natural ventilation are more difficult to simulate and validate due to the complex, non-linear relationship between wind forces and thermal buoyancy. The aim of this paper is to demonstrate the use of TRNLizard, an integrated thermal, daylight and airflow simulation tool based on Rhinoceros 5, Grasshopper, TRNSYS18, DaySIM and TRNFlow to develop and validate the concept for an energy efficient office building with a healthy, comfortable environment. The office building is located in Germany with a highly glazed façade and night ventilation for passive cooling. It is shown that night flushing reduces annual end-use cooling energy and peak cooling load of mechanical air conditioning systems by 55% and 15%, respectively.

Daylighting Metrics: an Approach to Dynamic Cubic Illuminance

Advances in research work in the field of numerical analysis of daylight performance have generated in-depth knowledge on photometric measurements of daylight quality. Most dynamic metrics are based on illuminance, which is a two-dimensional concept insofar as it is concerned with the density of luminous flux incident at a point on a surface. In order to extend dynamic metrics into the third dimension and consider the distribution of illumination at a point in space, it is important to generate new advances in simulation environments and consider spatial illumination metrics. In this context, the main objective of the present work was to advance in the development of cubic dynamic daylight metrics, as a complement to the two dimensional analysis currently employed, promoting the use of Climate Based Daylight Modelling (CBDM). For this purpose, cylindrical to horizontal illuminance ratio is applied to dynamic simulation paradigm developing the concept of useful modeling indexs (UMIs). The research methodology applied in this work is divided into two main parts: (i) two dimensional concept: spatial daylight autonomy (sDA(300lx,50%) -horizontal-, sDA(175lx,50%) -vertical-) and uniformity, and (ii) three dimensional concept: useful cylindrical to horizontal illuminance ratio (uEcl/Eh(0.3-0.6)). In order to assess this method, two spaces (RR1 and RR2) of the Lavalle Public Library, located in Mendoza-Argentina, were taken as a case study. Results show important differences in horizontal illuminance between RR1 and RR2 (∆sDA(300lx, 50%) &gt; 80%). Similar values of uEcl/Ewp(0.3-0.6) -useful cylindrical to horizontal illuminance ratio- are detected in both rooms (RR1= 69.32 % and RR2= 72.24 %) in nodes near north opening. Yet there are significant differences (&lt; 36%) of uEcl/Ewp(0.3-0.6) between nodes located near the south wall, this is due to the obstruction of a south opening in RR2. Furthermore, it is important to mention that 2D metrics display a more uniform behavior than 3D metrics. This shows itself clearly if we take into account that difference in sDA are much lower than difference in uEcl/Eh(0.3-0.6), if we compare nodes closest to the north windows to does that are far from it, in both rooms (RR1 and RR2). This results from the fact that cubic metrics are more sensitive to the direction of light. This is of crucial importance for daylight studies in clear sky condition, due to the defined direction of direct solar radiation. Finally, a new approach to daylighting performance analysis based on the addition of cubic metrics to dynamic daylight paradigm is proposed: useful modelling indexs (UMIs). UMIs make it possible to quantify annual occurrence of proper light modelling conditions. As an initial approach, cylindrical to horizontal illuminance ratio (Ecl/Ewp(0.3-0.6)) has been considered, due to its current use in international standards.

Daylight Performance of Classrooms in a Mediterranean School Heritage Building

In school buildings, natural light has considerable physiological benefits, and increases energy efficiency while reducing the operational energy consumption of buildings. It is thus crucial to maximize the amount of daylight, as well as to improve its quality, in educational premises. In Italy and other European countries, many historic buildings are reused as school buildings, changing their original function. This process of adaptive reusing is one method for conserving heritage buildings, however sometimes this process sacrifices the quality of daylight and well being of pupils. It has therefore become apparent that it is difficult to reconcile the cultural value of historic buildings with comfort standards. This study aimed to investigate the natural lighting performance of a school located in an historic building, and proposes different technological solutions to improve the visual comfort in classrooms whilst also respecting the cultural value of built heritage. Daylight performance was carried out in a representative classroom in the ‘Caserma Gaetano Abela’, an historical building located in Siracusa (Italy). A daylight model built in Radiance was first validated against an illuminance measurement campaign, and was then used to run detailed dynamic simulations. Climate Based Daylight Modelling (CBDM) metrics were used to show the achievable improvements in visual comfort conditions by means of proposed retrofit interventions. These interventions may also be used in other areas of southern Europe with similar climatic and constructive/distributive characteristics of architectural heritage.

Daylight Performance of a Translucent Textile Membrane Roof with Thermal Insulation

Daylight usage in buildings improves visual comfort and lowers the final energy demand for artificial lighting. The question that always occurs is how much conservation can be achieved? New or rare materials and constructions have a lack of information about their application. Therefore, the current investigation quantifies the daylight and energy performance of a rare multi-layer textile membrane roof. A translucent, thermal insulation with a glass fibre fleece between the two roof membranes combines daylight usage and heating demand reduction. A sports hall built in 2017 is used as a case study building with 2300 m2 membrane roof surface. The optical properties of the roof construction were measured with a total visual light transmittance τv of 0.72% for a clean surface. A climate-based annual daylight modelling delivers daylight indicators for different construction scenarios. The results show that, in comparison to only one glass façade, the additional translucent and thermally insulated membrane roof construction increases the annual daylight autonomy (DA700) from 0% to 1.5% and the continuous DA700 from 15% to 38%. In the roof-covered areas of the sport field, this results in a 30% reduction of the electricity demand for artificial lighting from 19.7 kWhel/m2/a to 13.8 kWhel/m2/a, when a dimming control is used. The study also found that the influence of the soiling of one layer decreases its light transmittance by a factor 0.81. Two soiled layers lower τv by a factor of 0.66 to 0.47%. This increases the electricity demand for lighting by only 12%. The results should be very valuable as a comparison and benchmark for planners and future buildings of a similar type.

Simulasi Desain Fasad Optimal Terhadap Pencahayaan Alami Pada Gedung Prodi Arsitektur Universitas Malikussaleh

The department of architecture’s building of Malikussaleh University was found problematic with its daylighting distribution through out the spaces. Also, earlier research had acknowledged the situation. However, the previous research did not offer an appropriate solution particularly regarding its optimum façade design. This research attempted to optimize the daylight harvest into the spaces by comparing its façade design for daylighting. There were three types of façade designs, perforated, vertical and horizontal screens, examined fot its most optimum daylight harvest. This study utilized digital simulation using Grasshopper and Ladybug Tools to calculate Annual daylight condition within the building. Within the tools this study integrated Climate Based Daylight Modeling (CBDM), which was Useful Daylight Illuminance (UDI) for the condition of Lhokseumawe. Next, it compared and suggested the result for the three types of façade design for optimum daylight distribution. Based on UDI, the targetted optimum daylight was in the range of 100-2000 lux. It was discovered that horizontal screen work best to almost entire building façades which covered 13 out of 15 examined-spaces within the building.

Application of Climate Based Daylight Modelling to the Refurbishment of a School Building in Sicily

This paper aims at promoting the use of Climate Based Daylight Modelling (CBDM) and related state-of-the-art metrics by discussing a range of design options to improve daylight fruition in rooms with different orientation, shape, function, and furniture of an elementary school that is located in the Mediterranean climate of Agira (Italy). The local climatic conditions, with clear skies for most of the year, require the integration of different shading and re-directing systems with the existing envelope and rooms’ layout. Results show that the dynamic modelling is a powerful and ‘creative’ tool in the designer’s hands, which helps to inform about the choice of the most appropriate technological solutions and on their architectural integration. Comparison with mostly used static daylight metrics, such as the average Daylight Factor (aDF) and the Uniformity Ratio (UR), reveals a contrast with what would be suggested if considering these metrics alone, as prescribed by the Italian legislation. These outcomes rebate the need of performing more accurate and dynamic daylight simulations using recorded (i.e., varying) rather than fixed sky conditions to correctly inform the design process.

Design and development of a low-cost angular sky luminance measurement system

Energy efficient building design requires simulated assessment of overall performance through reliable models, taking into account the daylight variations along with other significant parameters such as ventilation, plug loads and occupant behaviour. A robust indoor daylight model applicable to locations across the globe needs to incorporate local variations of sky luminance on a spatial and temporal basis, and needs an affordable system for dynamic angular daylight measurement to be used as part of a wider distributed network. In the present work, a low-cost prototype based on Light Dependent Resistors for measurement of angular daylight luminance distribution is developed and analyzed. This device was used to capture the angular analog data for 221 sky segments (20 azimuthal x 11 altitudinal segments and Zenith). The analog data was further converted to luminance data, and the visualized data was compared with sky-dome photographs and also with simulated polar daylight maps for a few Commission International de l’Eclairage (CIE) skies. The repeatability of the experiment was assessed by comparing the luminance data for selected sky segments over multiple time-segments for consecutive days. Measured data was found to be an acceptable fit with the CIE-models over various time segments, validating the prototype.

Sky Luminance Measurements Using CCD Camera and Comparisons with Calculation Models for Predicting Indoor Illuminance

In this study, we address the algorithm of the calculation formula from sky luminance distribution to vertical illuminance and indoor illuminance. To predict daylight, studies about sky luminance distributions and the DeLight daylight model were investigated. This paper compared three well-known sky distribution models (Perez model, Igawa model, and CIE standard sky model) with measured data. The charge coupled device (CCD) camera was used as a measurement method for sky luminance distribution. Indoor illuminance values calculated with those well-known sky distribution models are compared with measured indoor illuminance data. The following conclusions were obtained: (1) In the results of R2, mean bias error (MBE), and Cv(RMSE) analysis, the CIE standard sky model showed the lowest error rate with measured data. Between the Perez model and Igawa model, the Igawa model showed a lower error rate; (2) When we compared the sky classification of the Perez model and the Igawa model, both models classified the sky similarly to the CIE standard sky model in March. However, the classification of the sky in the CIE standard sky model, the Perez model, and the Igawa model differed in some of the July data because of high solar elevation; (3) The illuminance of the center point of the room was calculated using the well-known sky luminance distribution model, the Igawa model has a lower error rate than the Perez model in Korea.

Some simple methods for reducing daylight simulation time

ABSTRACTA significant barrier to routine use of Climate-Based Daylight Modelling in early design is the long time that it takes to run full annual simulations. Quick checks of design ideas are thus inconvenient, which discourages examining large numbers of design options or doing routine sensitivity analysis. Two ways of reducing required simulation time are to not simulate all the daytime hours of the year, or to simulate far fewer grid ‘measurement’ points. This paper demonstrates the effectiveness of taking smaller samples of random days throughout the year to reduce simulation time. By using a selection process to select “representative” samples of hours, simulations using only 5 days/month provide results with <6% error in performance estimates – well within accepted tolerances. The paper also shows the insignificant difference in design information provided by oft-recommended dense sensor grids compared to a 5 × 3 or 10 × 5 grid across a room plan.

An integrated method and web tool to assess visual environment in spaces with window shades

The current article presents a synthesis of the most recent metrics (visual comfort autonomy, lighting energy use, and view clarity) for assessing the visual environment performance of spaces with window shades, in the form of an integrated framework—interactive web-based tool. A daylighting and glare simulation model is used to calculate interior daylight distributions, luminance mapping, and annual spatial visual performance metrics. Then, a decision strategy was developed for selecting fabric properties based on different priorities: maximizing outside view, maximizing energy performance, or a balanced approach with fixed or flexible criteria to avoid compromises, all under visual comfort constraints. The models and decision strategies were implemented into a web-based tool, which includes a database of different design configurations (climate, envelope configuration, orientation, glazing size and properties, comfort restrictions, occupant view directions, etc.) and either provides recommendations for selecting shade properties based on the variation of the three visual performance metrics, or compares different configurations with detailed output information. The tool, under further development, is currently available to the public and can be used to obtain preliminary information about the comfort, energy, and view clarity performance of spaces will roller shades, without the need of high expertise or complex simulations.

Developing an advanced daylight model for building energy tool to simulate dynamic shading device

Recent developments in materials engineering create a possibility of new building envelope systems to increase various aspects of building performance. One of the recent developments is a dynamically responsive material that changes its phase based on ambient environmental conditions. This is a major development in materials engineering, and exemplifies a material that responds to ambient temperature and changes its shape. This is a good candidate as a shading device that changes its location to block or allow sunlight during the daytime, to increase visible and thermal comfort of indoor spaces.Current building simulation tools are limited in testing new materials. The major hurdle is that existing building simulation tools are developed for conventional materials and have difficulties in modeling new dynamically responsive materials. This paper presents a method to capture the complexity of physical behaviors in new material through building energy simulations. A more efficient simulation tool to test new materials will allow for more reliable results and the advancement in innovative building materials.This paper develops a method to evaluate a new daylight control system that includes an analysis of a new dynamically tunable material. To assess the daylight control system composed with the new material, the paper integrates a daylight model, a whole-building energy model, and a Kriging model to evaluate the new system’s performance.

Daylighting buildings: Standards and the needs of the designer

Despite widespread research on daylighting, there are insufficient data to justify a definitive statement on daylighting design criteria. This paper reviews the requirements for daylighting codes and guidelines, doing so from two different viewpoints. The first considers standards and regulations, the second is focused on development and the scope of climate-based daylight modelling.