Workplane Illuminance Research Articles

On the interaction between lighting and thermal comfort: An integrated approach to IEQ

A sustainable building design should be compliant with the even more pressing energy saving requirements – as in NZEB – and high levels of Indoor Environmental Quality. Despite it is accepted that different facets of IEQ could have antagonistic effects on building energy demand, relatively few studies are aimed at investigating the mutual interaction among its four components. From this point of view, the hue-heat hypothesis is based on the idea that light and colors can affect the thermal perception. Particularly, spectral power distributions of light shifted to short wavelengths seem to promote a cooler thermal perception and vice-versa. To verify this still debated hypothesis, this paper is focused on a subjective investigation carried out in a special mechanically conditioned test room provided with white-tuning LED sources. 163 volunteers have been exposed to two different lighting scenarios characterized by warm (3000 K) and cool lights (6000 K) at a fixed work-plane illuminance value (300 lx) at two different operative temperature values (20 °C and 25 °C). Obtained results seem to confirm that warm light results in a warmer thermal sensation. Probably due to thermohygrometric conditions relatively close to comfort, no effects on thermal evaluation, and thermal preference were found under both microclimatic scenarios. This was also about the effects of CCT on humidity perception and game performances.

Ceiling and Wall Illumination, Utilance, and Power in Interior Lighting

The common use of electric lighting in interiors has led to the need to search for user- and environmentally-friendly solutions. In this research, the impact of the luminaires and room parameters on the selected parameters of general lighting in interiors was assessed. To achieve the objective of this work, a computer simulation and statistical analysis of results were conducted. The illuminance uniformity on work plane, ceiling and wall relative illuminances, utilance, and normalized power density of lighting installations for 432 situations were analyzed in detail. The scenarios were varied in terms of room size, reflectance, lighting class, luminaire downward luminous intensity distribution, and layout. The lighting class was a factor having the highest impact on ceiling and wall illumination, utilance, and power. It was also shown that the impact of lighting class on ceiling illumination, utilance and power, was different in interiors of various sizes. The impact of reflectances and luminaire layouts on the analyzed parameters was significantly lower. The results also demonstrated that the use of different lighting classes gave the possibility of reducing the power of general lighting in interiors at a level of 30% on average. Based on the results, a classification of energy efficiency in general lighting in interiors was also proposed. Understanding the correlations between the lighting system used and the effects achieved is helpful in obtaining comfortable and efficient lighting solutions in interiors.

Evaluation of Illuminance Measurement Data through Integrated Automated Blinds and LED Dimming Controls in a Full-Scale Mock-Up

In this study, the indoor illuminance of a full-scale mock-up with LED system and external automated blinds was quantitatively evaluated by performing experiments involving integrated blinds and LED dimming controls. Actual illuminance experimental data were constructed and analyzed using commercialized blind control logic. The results revealed changes in the LED dimming ratio (turning-off ratio), and that the indoor illuminance required for the indoor space of 500 ± 30 lx could be secured in all cases when daylight was introduced according to weather conditions. It was found that because the angle and vertical position (VP) were fixed, manual blind controls could not efficiently use daylight, even though they could cut off solar radiation. When the blinds were automatically controlled in three-steps based on the exterior vertical illuminance under clear sky, the dimming rates of Zones A and B were found to be 68 and 50%, respectively. When the blinds were automatically controlled in four-steps, the dimming rates of Zone A (1.5 m from the window) and Zone B (4.5 m from the window) were found to be at 70% and 52%, respectively. If the VP and slat angle could be adjusted without lowering all the blinds, it would be possible to secure work plane illuminance, because the inflow of daylight increases, without the direct impact of direct sunlight and glare. These results indicate that integrated blinds and LED dimming controls can contribute to maintaining standard illuminance and saving lighting energy using daylight.

Performance Evaluation of Control Methods for PV-Integrated Shading Devices

This study aimed to develop a building-integrated photovoltaic (BIPV) device and optimal control methods that increase the photovoltaic (PV) efficiency and visual comfort of the indoor space. A louver-type PV-integrated shading device was suggested and an artificial neural networks (ANN) model was developed to predict PV electricity output, work plane illuminance, and daylight glare index (DGI). The slat tilt angle of the shading device was controlled to maximize PV electricity output based on three different strategies: one without visual comfort constraints, and the other two with visual comfort constraints: work plane illuminance and DGI. Optimal tilt angle was calculated using predictions of the ANN. Experiments were conducted to verify the system modeling and to evaluate the performance of the shading device. Experiment results revealed that the ANN model successfully predicted the PV output, work plane illuminance, and DGI. The PV-integrated shading device was more efficient in producing electricity than the conventional wall-mount PV systems, the control method without visual comfort constraints was most efficient in generating electricity than the other two with such constraints, and excluding the constraints resulted in less comfortable visual environment and reduced energy benefit. From the results analysis, it can be concluded that based on the accurate predictions, the PV-integrated shading device controlled using the proposed methods produced more electricity compared to the wall-mount counterpart.

Occupant-centered optimization framework to evaluate and design new dynamic shading typologies.

Dynamic solar shading has the potential to dramatically reduce the energy consumption in buildings while at the same time improving the thermal and visual comfort of its occupants. Many new typologies of shading systems that have appeared recently, but it is difficult to compare those new systems to existing typologies due to control algorithm being rule-based as opposed to performance driven. Since solar shading is a design problem, there is no single right answer. What is the metric to determine if a system has reached its optimal kinematic design? Shading solutions should come from a thorough iterative and comparative process. This paper provides an original and flexible framework for the design and performance optimization of dynamic shading systems based on interpolation of simulations and global minimization. The methodology departs from existing rule-based strategies and applies to existing and to complex shading systems with multiple degree-of-freedom mobility. The strategy for control is centered on meeting comfort targets for work plane illuminance while minimizing the energy needed to operate space. The energy demand for thermal comfort and work plane daylight quantity (illuminance) are evaluated with Radiance and EnergyPlus based on local weather data. Applied to a case study of three typologies of dynamic shading, the results of the methodology inform the usefulness and quality of each degree-of-freedom of the kinematic systems. The case study exemplifies the iterative benefits of the methodology by providing detailed analytics on the behavior of the shades. Designers of shading systems can use this framework to evaluate their design and compare them to existing shading systems. This allows creativity to be guided so that eventually building occupants benefit from the innovation in the field.

Sensor minimization method for integrated daylighting control by a mathematical approach

We proposed a simplified integrated daylight control (SIDC) system, which is a mathematical daylight control approach for multiple personal offices that use a couple of sensors installed in the outside of buildings. After the window plane illuminance that could reflect the external obstruction and the solar position was predicted, the correlation between the window and the work plane illuminance was analyzed through the pre-calculation phase. We allowed this correlation to reflect the roller-shade position. The roller-shade control approaches were proposed using two methods: one is a method of control via the position of the sun, and the other is a method of control via effective window plane illuminance based on the discomfort illuminance level of the work plane. After simple equations to predict the work plane illuminance according to the roller-shade positions in the pre-calculation phase were derived, the SIDC system was controlled with one of two roller-shade control methods. We used climate-based simulations for verification. As a result, roller-shade control using effective window plane illuminance was more efficient than control using solar position. 90.21% of all office hours were met with satisfactory visual comfort conditions. Energy usage was reduced by 86.96% compared to that of on/off control.

Analysis of the performance of prism daylight redirecting systems with bi-directional scattering distribution functions

Simulation with two types of bi-directional scattering distribution function (BSDF) was used to model the prism daylight redirecting fenestration (PDRF) in the indoor luminous environment. A goniophotometer was used to develop two different BSDF data sets: Klems data and Tensor tree data. Coefficient of determination and linear regression of the illuminance values with Klems and Tensor tree BSDF data were analyzed at low, medium, and high solar altitudes under Perez sky models with various sky conditions. The comparisons indicate that the Klems and Tensor tree angular data of PDRF materials show strong correlations and good linear regression relationships in general with PDRF daylighting clerestories. The study results demonstrated that using measured Klems data for combined daylighting and energy simulation of PDRF system is feasible as the simulated illuminance levels with Klems and Tensor tree data are similar under Perez sky conditions. The simulation results also showed that the PDRF daylighting windows above vision windows increase the work plane illuminance (WPI) opposite the window wall under clear sky conditions.

Experimental demonstration and performance evaluation of a complex fenestration system for daylighting and thermal harvesting

Two significant design strategies for mitigating building energy consumption are daylight redirection and solar energy harvesting. Effective daylighting implementation enhances the amount of useful natural light within a space and offsets the need for electric lighting. Solar energy harvesting systems can mitigate energy costs from mechanical systems by managing incoming thermal loads or capturing solar energy that can be used to supplement thermal systems in the building. While there are many available façade-based technologies that can perform daylighting or solar thermal energy harvesting, there remains a limitation in available systems that can perform both of them simultaneously. This paper, describes the design and experimental demonstration of a Liquid Filled Prismatic Louver (LFPL) system, which combines both energy-saving strategies. The LFPL system was installed in a south-facing room in New York City and evaluated for indoor daylight penetration and potential for thermal energy harvesting. Daylight redirection is achieved through the prismatic louver geometry and proper orientation, whereas thermal energy harvesting is achieved through IR absorption from the liquid (e.g., water) within the prisms. Daylighting performance was evaluated by illuminance measurements at key locations within the space, whereas thermal harvesting performance was evaluated through temperature measurements and thermal imaging analysis. We show that the LFPL system, with all prismatic elements oriented at the same angle, achieve a 2-fold and 8-fold enhancement in daylight redirection to the ceiling, for prism orientations of 10° and 20°, respectively. We also demonstrate the system’s capability to adjust to specific lighting needs, within the space, through the dynamic individual orientation of prismatic elements; thus, achieving a concentrated ceiling illuminance enhancement of ~100 times and ~200 times at 2.5 and 4.3 m away from the window sill, providing workplane illuminance enhancement of 6 and 2 times more than in the case of the control room with regular windows. Furthermore, we show a reduction of potential heating loads at locations close to the window from the combination of infrared absorption in the water volume and the redirection of the incoming solar radiation, leading to a reduction of the workplane temperature by an average of 7–10 °C.

Performance assessment of an active sunlight redirection system in areas with different climate: A comparison

The aim of this work is to assess the impacts, both in terms of daylight efficiency and energy impacts, of an advanced daylighting system that utilizes a heliostatic configuration for sunlight redirection in a deep South oriented office room in two (2) different climate conditions. Conventional daylighting systems such as windows, and clerestories placed on building facades, for a variety of reasons, have been proven ineffective in solving the problem of deep interior daylighting. This effect even with the use of modern daylighting techniques can effectively maintain the required illuminances. In such cases, systems that are designed to take advantage both the direct and diffuse natural light while maintaining and improving occupant visual comfort, particularly at greater distances from the external walls can provide higher work-plane illuminance levels deeper into the space. The results summarized here demonstrate that, if selected according to daylight climate and integrated appropriately with electric lighting controls, the system can enhance daylight in building interiors and thereby promote energy savings. It should be noted, however, that the performance of these systems is dependent on daylight availability. Nonetheless, the information presented in this paper demonstrates the potential benefits and shortcomings from the use of sunlighting technologies in different climate zones.

Daylight regulated by automated external Venetian blinds based on HDR sky luminance mapping in winter

Automated shading systems have the potential to exploit daylight in buildings to save energy of artificial lighting and cooling loads and improve occupants’f visual comfort. This paper investigates the daylighting performance of automated Venetian blinds based on sky luminance monitoring and lighting computation in winter. ‘fIn-situ’f experiments were carried out in a daylighting test module when the solar elevation angle was 21.7. at noon. Experimental results showed the automated shading was able to maintain work-plane illuminance within [500, 2000] lux range for 88% of the working time under a clear sky and for 83% of the working time under a partly cloudy sky, while mitigating discomfort glare for occupants.

Performance assessment of the BTDF data compression based on wavelet transforms in daylighting simulation

The bidirectional transmittance distribution function (BTDF), which is used to characterize the light transmission of a complex fenestration system (CFS), commonly involves bulky volume of data that can be a challenge to data storage and transmission in lighting simulation tools and on compact platforms. This paper introduces a compression scheme that is based on planar wavelet transforms with three levels of decomposition to efficiently compress the BTDF data of CFSs and maintain fidelity in daylighting simulation. The root-mean-square error (RMSE) and transmittance error (TE) of compressed medium-resolution BTDF data using three different wavelet bases were evaluated for five different CFS samples at various compression ratio. Based on the results, the generic error from compression did not exceed 20% with CDF9.7 basis for compression ratio up to 200. In the case of rendering an image of a scene in which a CFS was installed at the upper daylighting section of an unilateral façade, errors began to be noticeable at a compression ratio above 70. The uniformity factor g1 was discovered to be relatively sensitive to compression (below 15% error), while the average horizontal illuminance and daylight glare probability (below 10% error) were immune to compression ratio below 100. Compression was also evaluated for a high-resolution BTDF data of external Venetian blinds in the simulation of work-plane illuminance (WPI). With a HDR imaging technique based sky luminance map, the WPI simulation had unnoticeable errors for compressed BTDF data within a compression ratio of 100.

Split-pane electrochromic window control based on an embedded photometric device with real-time daylighting computing

Well-designed electrochromic (EC) glazing control can improve the energy performance of buildings and visual comfort of occupants in highly glazed buildings. This paper designed and demonstrated a compact integrated EC glazing automation system to control tint states of a split-pane EC window according to variations of sky conditions. The control is based on monitoring the luminance distribution of the sky and real-time lighting computation for a building interior, using an embedded photometric device (EPD). It optimizes tint states of EC glazing to offer sufficient daylight provision and temper discomfort glare for occupants, which potentially mitigates excessive solar heat gain. ’In-situ’ experiments were conducted in a full-scale testbed to demonstrate the daylighting performance under various sky conditions. Experimental results showed 83% of the working time for work-plane illuminance (WPI) and 95% of the time for daylight glare probability (DGP) were constrained in comfort range (WPI∈[500, 2000] lux, DGP ≤ 0.35) by the automated EC glazing (controlled by EPD) under clear skies; 68% of the time for WPI and 94% of the time for DGP in confined range under clear skies with thin clouds; 62% of the time for WPI and 85% of the time for DGP in confined range under partly cloudy skies.

Automated ‘Eye-sight’ Venetian blinds based on an embedded photometric device with real-time daylighting computing

Optimal shading control can improve occupants’ visual comfort and increase energy savings on artificial lighting and cooling loads during warm seasons. A highly integrated automated shading system is presented in this paper. Designed to regulate daylighting according to the varying sky conditions in decentralized applications, it optimizes visual comfort for occupants and maximizes their view outwards. The shading control is based on real-time lighting simulation for a building interior based on sky (and landscape) luminance distribution monitoring. Its lighting simulation quality was validated in a daylighting test module showing a 10% root-mean-square error in both work-plane illuminance (WPI) and daylight glare probability (DGP). Conducted under various sky conditions during summer, autumn and winter, the shading control demonstrated its capability in regulating daylight provision, mitigating excessive solar heat gain, tempering discomfort glare, and maximizing outside view for occupants with minimal delay. The results showed that the WPI was maintained within the range of [500, 2000] lux in 96% of working time under clear skies and in between 79% and 88% of working time under partly cloudy skies. The expected mitigation of cooling loads due to excessive solar heat gain (SHG) was estimated to reach 47% during a warm climate, compared with no shading protection. The automated shading system was also demonstrated to successfully occlude glare due to secondary reflections on specular surfaces from surroundings.

Optimum Glazing Configurations for Visual Performance in Algerian Classrooms under Mediterranean Climate

Daylight quality and quantity in Algerian schools show serious problems in ensuring visual comfort of students and teachers. Some problems are due to window design, which leads to excessive amount of sunlight penetration into the classrooms. The consequences are glare and heat gain. This study investigates the effective glazing pattern for classroom to achieve optimum daylight performance and visual comfort in Algerian classrooms. Field measurements of typical classrooms were carried out in a selected school in Algeria during solstice summer (under clear sky condition) and solstice winter (under overcast sky condition). The data of outdoor daylight illuminance were used to validate Integrated Environment Solution Virtual Environment (IESVE) daylight simulation. This study used three different glazing types, namely, clear, tint and reflective glass with different glazing proportions, subsequently, seven patterns of glazing window design were used for an extensive simulation exercise. The results of the investigation from the site measurements show that the work plane illuminance was found to be beyond the range of 300 lux to 500 lux, which exceeded recommended value, except for the south-east orientation with clerestory typology, which were recorded at 2.98% of daylight factor, in contrast the daylight uniformity in tested classrooms is appropriate. Furthermore, the simulation revealed that combination of 75% clear glass and 25% reflective glass with 30% wall-to-window ratio has achieved 41.41% during winter and 47.82% during summer of Useful daylight illuminance. The use of different glazing configurations shows a significant improvement on daylight distribution and the reduction of glare comparing to the reference model. However, such improvement in the quality and quantity of daylighting was inadequate which arises the need of further enhancement.

High-Performance Accuracy of Daylight-Responsive Dimming Systems with Illuminance by Distant Luminaires for Energy-Saving Buildings

In a conventional daylight-responsive dimming system (DRDS), all the luminaires are turned off during the calibration process except for the luminaire under consideration in order to sense only the workplane illuminance of that luminaire. However, the workplane illuminance of the luminaire is influenced by other luminaires. Therefore, the final workplane illuminance of the actual operated system is higher than the target workplane illuminance, reducing the energy-saving efficiency of the DRDS. Herein, to improve the conventional DRDS, an advanced commissioning prediction method of daylight illuminance, and a dimming control algorithm considering the influences by distant luminaires are proposed. To evaluate the accuracy of the proposed prediction method of daylight illuminance, the daylight illuminance on the workplane and the photo sensor values of six points were measured in a full-scale mockup for 27 consecutive days from 22 June to 18 July 2018. As a result of root-mean-square error (RMSE) analysis of daylight illuminance and the photo sensor values, the RMSE (64.86) of P3 located in the middle of the room was the highest, and the RMSE value (17.60) of P5 located near the window was the lowest. In addition, the power consumption of the luminaires, and the target illuminance accuracy of the proposed DRDS were measured and analyzed for 32 consecutive days from 19 July to 19 August 2018 in a full-scale mockup. The average target illuminance accuracy was 96.9% (SD 2.2%), the average lighting energy-savings ratio was 78.4%, and the daylight illuminance prediction accuracy was 95.5% (SD 3.4%).

Daylighting simulation for external Venetian blinds based on HDR sky luminance monitoring with matrix algebraic approach

An accurate daylighting simulation can potentially improve the quality of pre-planing buildings and regulating daylighting to achieve the goal of green buildings. However, standard sky models can hardly reproduce real skies in real-time for a specific location within its micro-climate. This paper investigates an embedded photometric device based on high dynamic range (HDR) sky luminance monitoring with high resolution mapping in simulating real-time horizontal work-plane illuminance distribution. To increase time efficiency in the iterative process for the illuminance calculation, a matrix algebraic approach was employed and adapted for the device. The photometric device was validated experimentally in a daylighting test module with external Venetian blinds at different tilt angle of slats. The results indicate the embedded photometric device based on monitored sky can improve accuracy in simulating real-time daylighting provision by over 3 times, with 15%∼37% average error, compared with a common practice using the Perez all-weather model.

Towards New Design of Laser Cut Acrylic Panels for Windows

Daylight quality and quantity in Algerian schools show serious problems in ensuring visual comfort of students and teachers. Some problems are due to window design, which leads to excessive amount of sunlight penetration into the classrooms. The consequences are glare and heat gain. This study investigates the effective glazing pattern for classroom to achieve optimum daylight performance and visual comfort in Algerian classrooms. Field measurements of typical classrooms were carried out in a selected school in Algeria during solstice summer (under clear sky condition) and solstice winter (under overcast sky condition). The data of outdoor daylight illuminance were used to validate Integrated Environment Solution Virtual Environment (IESVE) daylight simulation. This study used three different glazing types, namely, clear, tint and reflective glass with different glazing proportions, subsequently, seven patterns of glazing window design were used for an extensive simulation exercise. The results of the investigation from the site measurements show that the work plane illuminance was found to be beyond the range of 300 lux to 500 lux, which exceeded recommended value, except for the south-east orientation with clerestory typology, which were recorded at 2.98% of daylight factor, in contrast the daylight uniformity in tested classrooms is appropriate. Furthermore, the simulation revealed that combination of 75% clear glass and 25% reflective glass with 30% wall-to-window ratio has achieved 41.41% during winter and 47.82% during summer of Useful daylight illuminance. The use of different glazing configurations shows a significant improvement on daylight distribution and the reduction of glare comparing to the reference model. However, such improvement in the quality and quantity of daylighting was inadequate which arises the need of further enhancement.

Does typical weather data allow accurate predictions of daylight quality and daylight-responsive control system performance

Though Typical Meteorological Year (TMY) data is widely used for predicting daylight quality and daylight-responsive control system performance, few studies investigated whether the predictions were accurate. In this study, daylight simulation was performed for a real space using the TMY data and an actual local weather data with a one-minute interval. The former was used to predict the daylight quality, to design a closed-loop daylight-responsive dimming control system, to select the calibration hours, and to predict the control system performance; the latter was used to characterize the actual daylight quality and control system performance. Though the actual weather conditions can provide 30% higher daylight levels to the space, which seemed to suggest a potential to achieve a greater energy saving, none of the existing CBDM measures suggested such a difference. The TMY data was used to design a closed-loop dimming control system, to select the appropriate weather conditions for system calibration, and to predict the energy saving of the system by limiting the occurrence of over-dimming below 2% of the occupied hours. It was found the predicted energy saving was generally accurate if the system calibration was performed when the weather conditions were similar to those identified using the TMY data. When the calibration was performed under the inappropriate weather conditions, the system achieved lower energy saving and had a much frequent occurrence of over-dimming conditions. In addition, performing the system calibration under the weather conditions that resulted in higher photosensor signal to workplane illuminance ratios may be helpful to reduce the occurrence of over-dimming conditions caused by the larger variation of the weather conditions in reality.

Investigation of an integrated automated blinds and dimmable lighting system for tropical climate in a rotatable testbed facility

Performance of automated blinds and auto-dimming lighting system in providing lighting energy savings and occupant visual comfort was studied in a rotatable testbed facility located in tropical Singapore. The automated Venetian blinds system, consisting of a daylight-redirecting top portion and a glare-controlling bottom portion, was controlled by an in-house developed control algorithm designed specifically for tropical climate of Singapore to introduce maximum daylight while minimising Daylight Glare Probability (DGP). The auto-dimming lighting system used Digital Addressable Lighting Interface (DALI) controller to control T5 fluorescent and LED luminaries. Energy consumption by the lighting system, working plane illumination distribution and DGP were monitored by a network of sensors and high-dynamic range (HDR) camera systems. Compared to non-dimmable T5 lighting, LED lamps provided about 24% of lighting energy savings. Auto-dimming technology showed about 46% lighting energy savings. LED lamps coupled with auto-dimming showed around 80% lighting energy savings. Without window blinds, the working plane illuminance exceeded the recommended 3000 lx level during certain time of the day and DGP exceeded 0.35. The automated blinds effectively eliminated glare discomfort, and with the automated blinds working in conjunction with the auto-dimming, significant lighting energy savings was achieved without compromising the illuminance level at the working plane. 75% of lighting energy savings was achieved for North orientation and 63% for East orientation. Façade orientation was found to have a significant impact on the lighting energy savings potential, with the North orientation achieving higher daylight savings due to higher daylight redirection possibility throughout the day. The lighting energy savings potential is higher for clearer sky conditions due to higher daylight availability. Implementation of daylight re-directing shading system has significant lighting energy savings in the tropics. These lighting energy savings can be captured by deploying an auto-dimming system. With careful design of the system and control algorithm, the lighting energy savings can be achieved while maintaining good visual comfort.

Design and validation of a compact embedded photometric device for real-time daylighting computing in office buildings

Studies have shown that the exposure to daylight can have substantial visual/non-visual benefits for building occupants. To optimise daylighting provision while maintaining a comfortable visual environment, daylighting control systems have been investigated by architectural design and academic research for a number of years. However, real-time regulation of daylighting in buildings requires transient daylighting simulation with high accuracy and, daylighting simulation, as performed to date, is significantly impacted by the employed sky luminance distribution models which only crudely reproduce the real sky characteristics due to oversimplification and limited luminance sampling inputs.In this paper, an embedded photometric device is proposed to combine high dynamic range (HDR) imaging based high-resolution sky luminance monitoring with quasi real-time on-board daylighting computing, composed of a low-cost image sensor and a field programmable gate array (FPGA) micro-processor. A deliberate calibration procedure of the whole imaging system, regarding its spectral response (spectral correction error f’1 = 8.89%), vignetting effect and signal response, was formulated and validated experimentally. The device was made to measure a wide luminance range (150 dB) including that of the direct solar disk, sky vault, and landscape simultaneously. Finally, experiments during predominant clear and overcast sky conditions were conducted respectively to assess its performance in daylighting simulation, both qualitatively and quantitatively. The experimental results demonstrated its quality in solar tracking as well as its capability to reduce daylighting simulation error to 17∼13 of that of a common practice using the conventional Perez all-weather sky model for workplane illuminance calculation in office buildings.