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Light pipes are innovative daylight lighting systems often used linearly which transmit light through reflections on carrying surfaces. However, in order for the system to be used in more complex buildings, it should be possible to integrate one or more elbows into the system if needed with the purpose of deliberately change the direction of light transmission. In this study, attention is drawn to the assumption that the light carried in the elbowed light pipes is related to the design of the elbow geometry as well as variables such as pipe length, diameter (aspect ratio), reflectance and transmittance values of the components, sky conditions, solar angles, latitude-longitude data, elbow angle, etc. The purpose of the study is to investigate the daylight performance of elbowed light pipe system and different elbow geometries. In this respect, the models used in scientific studies and commercial products were compared and new elbow models were proposed. Daylight levels (lux) and Daylight Factor (DF) achieved through a numerical simulation software based on a correct method and well-established algorithm were evaluated as performance measures. Whether the light levels reached as a result of the analyses alone are sufficient to illuminate the space varies depending on the dimensions, function and duration of use of the space. [ABSTRACT FROM AUTHOR]

• TDDs require smaller roof opening, provide light deeper than conventional skylights. • Evaluation of light delivery and visual comfort performance of TDDs under real sky. • Studied influence of TDD dome, diffuser, diameter and other factors. • Prismatic domes provide more rounded daily illuminance profile. • No visual discomfort detected. Tubular daylight devices (TDDs) require a much smaller roof opening than conventional skylights and, because of their highly reflective tube, they can deliver daylight farther away from the building envelope. This can provide lighting energy savings, increasing resilience in new and existing buildings. Different types and configurations are available amongst commercially available TDDs, including domes/diffusers with varying optical properties and the diameter of the TDD. This paper presents a comprehensive experimental evaluation of the lighting and visual comfort performance of multiple configurations of commercially available TDDs, varying dome type (prismatic and clear), diffuser type (Fresnel and prismatic), and diameter (53 and 35 cm), under a range of environmental conditions (different times of day/year, sky cover). Based on illuminance measurements, estimated lighting energy use is also presented. Results indicate that, for clear sky, light levels increase and energy use decreases with solar altitude (e.g., 16 Wh/m2 daily energy use intensity on a high maximum daily solar altitude (MDSA) day and 34 Wh/m2 on a low MDSA day) and TDD diameter (e.g., 34 Wh/m2 and 69 Wh/m2 for 53 cm and 35 cm TDDs, respectively, for low MDSA). The daily illuminance profile is more rounded for prismatic domes and has higher peaks for clear domes; this translates into a somewhat higher average daily useful daylight illuminance (DUDI) for prismatic domes (86 %) when compared to clear domes (80 %). No clear impact of diffuser type was apparent. Measurements indicated no discomfort glare for any of the conditions tested. [ABSTRACT FROM AUTHOR]

Light pipes are more and more used for underground lighting as a way of daylighting. The luminous environment of mine will be greatly improved if this technology can be applied in the mine underground spaces. However, the tube transmission efficiency is low in the morning, evening and the whole winter because of the low solar altitude. More sunlight was introduced into the room by adding reflectors inside the dome of light pipes. Considering the change of solar altitude angle and azimuth angle, TracePro software was used to simulate the influence of different domes and reflectors on the daylighting efficiency of light pipes under direct sunlight in sunny days. The simulation results show that after adding reflector into spherical dome, the daylighting efficiency can be improved by 13. 52% on the vernal equinox and 79. 56% on the winter solstice, while drop by 4. 11% on the summer solstice. Experimental measurements were carried out in two offices in Tongzhou, Beijing, China including clear and cloudy days. On sunny days, the average incident luminous flux could be increased by 8. 67% by adding reflectors, and the error between the simulation results and the measured results was less than 20%, which verified the reliability of the model. On cloudy days, the incident luminous flux introduced was reduced after adding reflectors, indicating that reflectors are not conducive to the collection of diffuse light. Besides weather and solar movement rules, the length of the light pipes also has a great impact on the daylighting efficiency of light pipes. How to ensure the daylighting efficiency under the condition of long-distance needs further research. [ABSTRACT FROM AUTHOR]

Highlights • Performance evaluation of structurally modified light-pipe. • The study has been done for a composite climate with clear sky condition. • The study focusses on the mode of saving energy by utilizing day-lighting techniques. • Ray-tracing simulations provided an enhanced analysis of the opto-mechanical properties of different light-pipes. • Improvement in day-lighting utilisation through modified light-pipe has been supported by simulation and experiments. Abstract Nowadays, an escalation in the development of day-lighting systems is observed as people are fascinated towards day-lighting incorporation so as to get benefitted of the lighting energy savings, along with other intangible benefits like health, well-being, and productivity of the occupants. Light-pipe is one such day-lighting system that enables the natural light to enter the spaces which are located far away from the periphery area of a building and thus, cannot be illuminated by windows or other daylighting devices. Light-pipe, while illuminating the interior spaces, also blocks UV rays, which contributes to the heat gain of a room. The study focuses on the design, optimization, simulation and experimental evaluation of the modification in the conventional light-pipe design towards achieving more light through the pipe. This includes modeling of several structural design modifications in light-pipe and their corresponding ray-tracing simulations in TracePro. Out of these modifications over the conventional straight pipe, the design with the best results has been selected and developed so as to experimentally validate the simulation results. The simulation as well as experimental evaluation of the modified light-pipe in comparison to the conventional light-pipe in terms of the average internal illuminance of the room and the light transmission efficiency of the light-pipe indicates an improvement with the modified design of light-pipe. [ABSTRACT FROM AUTHOR]

Light pipes are popularly used for transporting outdoor sunlight into deep spaces of the building, and hence, use of artificial lighting could be substantially reduced. Performance prediction of a light pipe is an essential step before its use in buildings, so that energy saving potential of the light pipe could be quantified. This paper deals with experimental validation of three existing semi-empirical models for light pipes with different aspect ratios, installed on a windowless test room, at IIT Delhi, New Delhi. Two new semi-empirical models based on the existing correlations are developed. The new model found to perform better with mean bias error (MBE) and root-mean-squared error (MSE) of 0.076 and 0.01, respectively. The better performing new model is used for the evaluation of hourly internal illuminance by the light pipe in a typical meteorological year (TMY) in New Delhi. From hourly internal illuminance in a typical meteorological year, the energy saving potential and CO2 mitigation potential of light pipe system for the test room are evaluated. Monthly average energy saving potentials of the light pipe-fluorescent tube light system are found to be 50% for continuous dimming control and 38% for three-step on-off control. Results show that the light pipe-fluorescent tube light system, with different lighting controls, could reduce CO2 emissions to 15-50%. [ABSTRACT FROM AUTHOR]

Tubular Daylight device (TDD) and solar water heater (SWH) are two power saving solutions that are commonly employed individually in residential and industrial premises. This paper proposed a novel merged power saving system consisting of TDD and SWH in one model, which is the first attempt to integrate these two systems. The idea of merging the TDD with SWH is based on utilizing the existing area around the TDD to implement the SWH around the TDD tube through a serpentine collector. The main purpose for such integration is to enhance solar energy saving, space area saving, and to decrease the fabrication cost. The illumination and thermal performance of the new proposed model were tested and analysed experimentally in different seasons in Cairo - Egypt to assess its performance in practical use. The obtained results indicated that the merged system succeeded in transferring an acceptable illumination rate and increasing the water temperature. The transferred internal illuminance has reached approximately to 6.5 W/m 2 that fulfils the required needs of lighting. Additionally, the system increased the water temperature up to 62 °C, with a performance instantaneous efficiency that reached 21.17% which is very satisfactory. Furthermore, the performance of thermosyphon SWH with different serpentine collector coil number of turns has been evaluated. The results proved that, the collector number of turns has significantly affected the SWH performance in a directly proportional relation. [ABSTRACT FROM AUTHOR]

A comprehensive study of straight light pipe efficiency and illuminance distribution below ceiling level is performed using HOLIGILM tool. The recommendations for light guide systems can be made for different latitudes and sky luminance patterns using the data computed here. The computational results show that the light pipe transmittance is a monotonic function of solar altitude, except for low-sun angles. Redistribution of photons at the light pipe base can be characterized by a scalar value called “asymmetry parameter”, g . A use of g is an efficient attempt to the classification of a large number of luminous intensity distributions. The minimum value of g is at low solar elevations (between 10° and 30°) because of balanced contribution of diffuse light of a sky and the direct sunbeams. The low values of g indicate the redistribution of light is more uniform. Luminous intensity solid determined by means of HOLIGILM tool is used to compute illuminance distribution at a working plane. The peak intensity and intensity gradient of a bright ring projected onto a working plane can be used to characterize the optical properties of different light pipes in different climatic zones. [ABSTRACT FROM AUTHOR]

The vertical straight pipes are a desirable technology for delivery daylight into interior spaces because this concept benefits from luminance distribution of the whole upper hemisphere, including sunlight that is most important source of light under clear sky conditions. Vertical pipes can transport sunbeams to deep interiors independent of solar azimuth and/or room orientation. Currently, the tools for modelling different pipes are widely available, but their accuracy decreases as the aspect ratio of a light-pipe increases. In sunny environments with high solar altitudes and favorable clear skies the tubular light-guides allow to deliver daylight into deep offices, halls, or even underground spaces in building cores. The optical efficiency of such systems strongly depends on number of reflections the beams undergo on their path from the top to the bottom of a light pipe. In general, dense-grid and high CPU requirements meet when accurate numerical predictions are required. Such computations are non-attractive if intended for routine (mass) modelling. In this paper we introduce an analytical solution to the optical efficiency of straight pipes that is applicable to all aspect ratios and provides accurate predictions with very low demands on processor time. The new analytical model is validated and benchmarked against accurate HOLIGILM calculations, while showing the percent deviations are kept below 10% for most cases studied. [ABSTRACT FROM AUTHOR]

Ballooning in fuel clad and pressure tubes of light water reactors due to the Loss of Coolant Accident (LOCA) has been a topic of intense research for the past few decades. The possibility of the phenomenon in fast reactors has been ignored due to the preclusion of LOCA in the design relatively low operating pressure and better high temperature resistant structural materials. Albeit these merits, the high burn-up, high flux and therefore, high temperature in fast reactors poses an onus to the fuel clad. The key question is thus whether ballooning will take place in fast reactors and at what conditions. Experimental investigation of the behavior of the clad tubes at various operating conditions of pressure, temperature and heating rates suggest that ballooning takes place in fast reactor fuel clad at higher burn-up (which results in an increase in pressure and temperature of the clad tube) and lower heating rates. This paper gives an insight into the first of its kind approach for the investigation of ballooning in fast reactors using the Rupture And Ballooning In Tubes (RABITS) facility which is indigenously developed. It is observed from the experimental results that the rupture life of the clad at high temperature, i.e. 950 °C, is considerably lower than that predicted by the creep rupture equation available for the material. This reduction in life of the clad is attributed to the change in damage mechanisms at higher temperature (∼0.6 T melting point ), which can be the damage due to the ballooning phenomenon. [ABSTRACT FROM AUTHOR]

An essential impact which can improve the indoor environment and save on power consumption for artificial lighting is utilization of daylight. Optical fiber daylighting technology offers a way to use direct daylight for remote spaces in a building. However, the existing paradigm based on the precise orientation of sunlight concentrator toward the Sun is very costly and difficult to install on the roof of buildings. Here, we explore an alternative approach using mirror-coated lens array and planar waveguide to develop a flat optical fiber daylighting system (optical fiber daylighting panel) with lateral displacement Sun-tracking mechanism. Sunlight collected and reflected by each mirror-coated lens in a rectangular lens array is coupled into a planar waveguide using cone prisms placed at each lens focus. This geometry yields a thin, flat profile for Sunlight concentrator. Our proposed concentrating panel can be achieved with 35 mm thickness while the concentrator's width and length are 500 mm × 500 mm. The commercial optical simulation tool (LightToolsTM) was used to develop the simulation models and analyze the system performance. Simulation results based on the designed system demonstrated an optical efficiency of 51.4% at a concentration ratio of 125. The system can support utilizing a lateral displacement Sun-tracking system, which allows for replacing bulky and robust conventional rotational Sun-tracking systems. This study shows a feasibility of a compact and inexpensive optical fiber daylighting system to be installed on the roof of buildings. [ABSTRACT FROM AUTHOR]

Light pipes can provide daylight and improve lighting conditions in buildings. Knowledge of their optical performance is a prerequisite for their successful integration into buildings. This article presents and analyses the experimental performance and the specific efficiency characteristics of a light pipe as integrated into an experimental test-cell. Extensive measurements are performed for eight continuous months under clear, cloudy and intermediate sky conditions. The spatial and temporal variability of the indoor illuminance is analysed using clustering techniques. It is found that there is an almost exponential relation between the average and the maximum indoor illuminance with the exterior illuminance levels. In parallel, a strong spatial inhomogeneity is observed under all sky conditions. The transmissivity or Daylight Penetration Factor of the light pipe is found to present a strong daily variation during the clear days while it was almost constant under cloudy sky condtions. A clear correlation of the light pipe’s Daylight Penetration Factor is found against the solar azimuh and solar altitude especially under clear sky conditions. [ABSTRACT FROM AUTHOR]

Tubular daylighting device (TDD) or light pipe is an effective way of energy saving and has been found increasing acceptance for indoor lighting. This article presents a new method to evaluate the TDD’s optical performance by the output luminous flux. The method is using position (α, d) and angular distribution of luminous flux (φ, θ, Φ) information to describe the optical properties of the TDD’s light collecting cover. With the optical information, the ray tracing simulates the output luminous flux basing on the structural and reflectivity of the light pipe. Our method makes a complete optical description of light ray passing through a top cover, thus enable the subsequent ray tracing of light pipe. As an application, lambertian beam pattern is used as light source which goes through from the cover, and then the results on various length to diameter ratios of light pipes are compared. [ABSTRACT FROM AUTHOR]

We introduce a way to simultaneously measure the light density, light vector and diffuseness of the light field using a cubic illumination meter based on the spherical harmonics representation of the light field. This approach was applied to six light probe images of natural scenes and four real scenes built in our laboratory, and the results were compared to those obtained using Cuttle’s method. We also demonstrated a way to simultaneously and intuitively visualise the global structure of the light distribution using light tubes and colour coding for the light density, light flow and diffuseness variations through the space. Together with Mury’s work, we have a complete way to describe, measure and visualise the local and global low-order properties of light distributions in three-dimensional spaces. [ABSTRACT FROM AUTHOR]

Film type panoramic aerial camera mounted on the aircraft is a fine optical instrument to photograph the ground scene, Dynamic resolution detection is an important judgment to evaluate the imaging quality when camera is in the flying situation or motion scene is imaged. According to its principle of work to design a set of indoor detection system with dynamic resolution detection. Based on the analysis of its working principle and performance index, The overall scheme of the dynamic resolution detection device is proposed. Far target simulation system-large field view parallel light pipe, dynamic graphics system and dynamic graphic generation system structure are designed in detail, Proposing the test method to core parameters of parallel light pipe and dynamic graphics generator, this detection system meet the needs of dynamic resolution detection By theoretical analysis and practical testing. [ABSTRACT FROM AUTHOR]

A coupled system consisting on a heliostat and a matrix of light-pipes inside one road tunnel where the heliostat injects sunlight, is proposed. Its reliability and efficiency from theoretical calculations and a mock-up, is analyzed as a function of tunnel orientation. The heliostat is fixed above the road some meters before the portal gate of the road tunnels. It continuously seeks the correct orientation so that the angle between sun, heliostat and light-pipes in the portal gate, injects of parallel sunrays every moment. Then, these rays are guided through the light-pipes and distributed on the road in the threshold zone with a remarkable improvement of the efficacy of light-pipes and the relevant savings in electrical consumption and number of luminaries. The results of calculations and measurements on mock-up, that show energy savings above 20% in the most favorable tunnel orientations and 14% in arbitrary orientations, as well as a discussion about the most accurate tunnel orientations are analyzed and presented. [ABSTRACT FROM AUTHOR]

In a concerning global energy context, the construction industry must be able to respond both in terms of energy management and the comfort of its buildings’ occupants. In this context, innovative devices using daylighting can provide an obvious answer. The Tubular Devices Guide Systems (TDGS) are innovative daylighting processes based on light transport. They offer a real response to the diurnal energy consumption (frequently in tertiary). However, today's design will make tomorrow's building. This is why it is necessary to better adjust our prediction tools to optimize the use of these technologies and their coupling to active processes (artificial lighting). The literature reveals a disparity in performance prediction tools for light pipes. Two causes are targeted: the adjustment of semi-empirical models and their accuracy. This article offers some solutions to both problems. We propose a new form of model (improved accuracy) associated with a generalized modelling protocol (response to the adjustment) through a model generator named HEMERA. Our approach is organized around a Galilean sequence, i.e., we rely on observation and results of an experimental study in real weather conditions to better understand the phenomena and validate the developed model. Energy autonomy and user comfort in the building are at the heart of our concern, and we will provide evidence to validate the use of TDGS in buildings. In this context, we propose an energy equivalence between the light pipe and artificial lighting. [ABSTRACT FROM AUTHOR]

Vibration fatigue failure is a critical problem of hydraulic pipes under severe working conditions. Strain modal testing of small and light pipes is a good option for dynamic characteristic evaluation, structural health monitoring and damage identification. Unique features such as small size, light weight, and high multiplexing capability enable Fibre Bragg Grating (FBG) sensors to measure structural dynamic responses where sensor size and placement are critical. In this paper, experimental strain modal analysis of pipes using distributed FBG sensors ispresented. Strain modal analysis and parameter identification methods are introduced. Experimental strain modal testing and finite element analysis for a cantilever pipe have been carried out. The analysis results indicate that the natural frequencies and strain mode shapes of the tested pipe acquired by FBG sensors are in good agreement with the results obtained by a reference accelerometer and simulation outputs. The strain modal parameters of a hydraulic pipe were obtained by the proposed strain modal testing method. FBG sensors have been shown to be useful in the experimental strain modal analysis of small and light pipes in mechanical, aeronautic and aerospace applications. [ABSTRACT FROM AUTHOR]

This paper describes recent research on the prediction of the performance of light pipes and the ways to optimise their design, in order to house artificial lighting, able to supplement daylight in a space. The research has resulted in an algorithm, for the easy and quick calculation of the interior illuminance provided by light pipes, and in a procedure for the calculation of the power of the necessary artificial lighting (light emitting diodes [LEDs]) and the energy savings for lighting, due to the daylight provided by the light pipes and the daylight linked controls of the LEDs. [ABSTRACT FROM PUBLISHER]

Double loaded corridors in educational buildings generally experience a low daylight level, as they do not have enough direct contact with the outdoor environment. The task light level in those corridors is lower than that in reading or office spaces. Double loaded corridors normally depend on artificial light. On the other hand, double loaded corridors need to be lit all the day during the occupation period as one can not specify when different users could use it. This research explores the possibility of using tubular light systems in addition to some architectural solutions to provide double loaded corridors with the required daylight. The research used anidolic, light pipe and ceiling cavity systems in addition to high windows from side offices to improve daylighting in double loaded corridors. The experimental study, which has taken place at JUST, showed that anidolic systems could provide double loaded corridors with sufficient lighting levels. On the other hand, radiance simulations showed that anidolic and some other solution systems can provide corridors with sufficient daylight in lower floors, while light pipes can provide corridors with sufficient daylight in upper floors. [ABSTRACT FROM AUTHOR]

The formation of light fields of various structure and real-time control of their parameters with the help of inexpensive and technologically simple adaptive devices is an urgent problem of modern optics. A 4-channel liquid-crystal (LC) modulator (LC focusing device) can serve as such a device. An analysis of longitudinal light lines and hollow light beams formed by this device is performed. Such fields are realized due to the possibility of creating a phase delay distribution over the aperture of an LC focusing device in the form of a truncated cone (quasi-axicon). Spatial and energetic characteristics of these light fields are considered from the standpoint of their potential applications in problems of three-dimensional manipulation. It is shown that by varying the voltages applied to the contacts of the focusing device it is possible to control the width of the light contour, the size of the zero-intensity region, the lengths of the light tube and light line segment, and the energy characteristics of the formed fields. The results obtained may be of use in the formation of three-dimensional optical traps in problems involving the manipulation of transparent and nontransparent micro-objects. [ABSTRACT FROM AUTHOR]

This paper presents a daylighting experimental analysis of a novel vertical light-pipe which incorporates side apertures serving multiple levels to a deep-plan building. A light-pipe system that serves three floors has been developed in which the ground floor is illuminated via a light-pipe by a conventional ceiling mounted diffuser while the first and second floors are lit with daylight outlets on the sidewalls. Illuminance at each level of the three storey building relative to a work plane height, as well as the distance from the luminance source have been determined. The relationship between illuminance level on the work plane and the aperture area for different vertical apertures has been found and the results are presented. To determine the ratio of aperture opening area, A o , to the work plane height, H wp , that produces the same illuminance at representative points on a desk at each level, a 1:13 scale model was built to avoid sensor sensitivity problems. A 75 mm-diameter tubing was used to construct a scaled-model designed to emulate the largest 1000 mm-diameter light pipe available, yielding the largest aspect ratio, and thus light transmission at a scale of 1:13. Experiments with outdoor illuminance levels of 11,000 and 14,000 lux gave illuminance at specified reference points of 532 and 80 lux respectively. Importantly, the methodology used in this research can be adopted by architects and building engineers when developing case-specific designs or redevelopment of existing buildings. [ABSTRACT FROM AUTHOR]

Performance of conventional vertical light pipes with acrylic domes is highly dependent on the solar altitude since for lower solar elevation the acceptance angle is limited due to the small inlet aperture. A profiled Fresnel collector with a multi-lens system is useful in enhancing light in a light pipe at low solar altitudes but suffers losses due to multiple reflections during transmission. In this paper we show that further enhancement of light during the morning and evening hours is possible by using a profiled Fresnel collector integrated with graded laser cut panels, i.e. laser cut panels with bands of varying depth to width ratio that can redirect low altitude sun rays axially down the light pipe. The effect of various depths to width ratios of the laser cut panel with respect to variation in incident light on the performance of a light pipe is also presented in this paper. The graded laser cut panel performed better than other laser cut panels. Optimum tilts of the laser cut panel at which maximum light is deflected for various incident angles of the source were identified. Maximum light output for the graded laser cut panel was for lower incidence of solar altitude angle. The graded/profiled laser cut panel was integrated with Fresnel north and south facing collectors and the performance was assessed in daylight. Good redirection of light was observed for the Fresnel collector in the morning and evening hours when compared to a light pipe with an acrylic dome or a Fresnel collector without a laser cut panel. The light is redirected more parallel to the axis of the pipe thus minimizing the reflections on the internal lining and thereby increasing the performance of the light pipe. [ABSTRACT FROM AUTHOR]

This paper examines the feasibility of using vertical light pipes to naturally illuminate the central core of a multilevel building not reached by window light. The challenges addressed were finding a method to extract and distribute equal amounts of light at each level and designing collectors to improve the effectiveness of vertical light pipes in delivering low elevation sunlight to the interior. Extraction was achieved by inserting partially reflecting cones within transparent sections of the pipes at each floor level. Theory was formulated to estimate the partial reflectance necessary to provide equal light extraction at each level. Designs for daylight collectors formed from laser cut panels tilted above the light pipe were developed and the benefits and limitations of static collectors as opposed to collectors that follow the sun azimuth investigated. Performance was assessed with both basic and detailed mathematical simulation and by observations made with a five level model building under clear sky conditions. [ABSTRACT FROM AUTHOR]

Nowadays, there exist many innovative daylighting technologies which could be used to enhance natural illumination for buildings that use more electric light during the day such as schools, industrial buildings. This study describes the passive zenithal light pipe daylighting technology’s performance through the scale model method. The yield of passive zenithal light pipe was improved and was achieved by incorporating a light collimator in the light pipe. Through the design and fabrication of the light collimator, illuminance in the classroom has been improved from 178 lux distributed by commercial diffuser to 370 lux (illuminance average from 9 a.m. to 4 p.m. under sunny days from October to December 2013). A range of reflector materials were tested on the interior lining of the collimator for consistent illuminance distribution and it was discovered that rough re-used aluminum cooking foil distributed uniformly and increased illuminance. All data used has been obtained from measurements at a test location in Stellenbosch, South Africa throughout the year. [ABSTRACT FROM AUTHOR]

Light pipes transmit daylight into building interiors. Their installation into thermally insulated roofs of low energy buildings can be a problem because of thermal bridges and condensation problems. This article is focused on a CFD simulation thermal analysis that includes four variations of light pipes with a segment of a flat roof. Common light pipes with a hollow light guiding tube were compared to special light pipes containing an additional glass unit located inside the tube. The additional glass units increase thermal resistance and reduce condensation risks of the light guiding systems. The light pipes were compared in two different simulation models run in ANSYS Fluent software and the CalA program. Temperature profiles and air flow patterns of the cross sectional profiles of the light pipes served to determine the total heat transmittance and heat losses of the studied light pipes installed in a segment of a thermally insulated flat roof. The paper compares simplified 2D rotational–symmetrical numerical model based on the thermal diffusion equation with the complex 3D CFD numerical simulation. The results confirm that the simplified 2D numerical model is suitable for the thermal evaluation of the light pipes containing an additional glass unit, too. The additional glass unit with the triple glass improves thermal resistance up to 88% in case of light pipe with diameter 600 mm and reduces optical transmittance to 28%. [ABSTRACT FROM AUTHOR]

Traditional windows, as the major source of daylight, have a common problem which is uneven distribution of daylight in the room. Several innovative daylighting systems such as light shelves, fixed and movable reflective louvres, reflective sills, prismatic glazing, light pipes, etc., have been developed to address this problem. This paper reports on a research programme that investigates retrofitted solutions to uneven distribution of daylight in deep-plan office buildings. The work presented here follows initial investigations into the design and applicability of an automated retrofitted panel thermal shutters which can also act as a sunshade and daylighting system. The system has a patented function which allows each shutter/louvre to be controlled and placed separately from other louvres. This study evaluates the effectiveness of the system when acting as a sunshade, light shelf, reflective louvre, and reflective sill under clear, overcast, and sunny sky conditions. According to the results, the system significantly improved daylight distribution and reduced the need for artificial lighting by 60%. [ABSTRACT FROM AUTHOR]

Abstract: Tubular daylighting systems are designed to guide light to the building׳s core using a highly reflective pipe. The intensity of the transmitted light is essential for the performance of the system. For the qualitative perception of the provided illumination, the color of the delivered light is also an important aspect. For highly reflective mirror light pipes, spectral variations are generally assumed not to affect the color of the transmitted light. Here, spectrophotometric measurements and ray tracing simulations of mirror light pipes are used to verify this commonly made assumption. The characterization methods employ spectral evaluations for both direct and diffuse incident light. The color properties are evaluated for mirror light pipes with a length to diameter aspect ratio of up to 16, using the CIE chromaticity diagram and CIELAB coordinates. For the xy chromaticity diagram, a larger color shift was noted for different illuminants than as a result of the optical properties of the reflective material. Using the CIELAB coordinates, a small color shift was noted for light incident at low solar altitudes. Overall, highly reflective films with spectral variations of a few percent do not markedly affect the color of the transmitted light. [Copyright &y& Elsevier]

Abstract: Tubular light guides represent a convenient concept for illumination of windowless parts of buildings by natural light. The transmittance of this optical device generally varies with geometrical characteristics as diameter and length and also with its properties. A high light transmittance of the roof dome and diffuser as well as high quality of the inner reflective surface facing of the light guiding central duct are required. External daylight conditions such as sky cloudiness or sky luminance distribution have undoubtedly a vital influence on the tubular light guide efficiency. A daylight computer simulation study focused on an evaluation of the tube light efficiency is presented in the article. The efficiencies of straight tubular light guides are computed for the standard overcast and clear sky luminance distributions. The results obtained can be useful for predetermination of a luminous flux emanating a light guide, for evaluation of indoor daylighting, and for elaboration of various daylight strategies. [Copyright &y& Elsevier]

This article presents the development and validation of a simplified model to compute the thermal characteristics (solar heat gain coefficient and thermal conductance (U-factor)) and surface temperatures of tubular daylighting devices. The model takes into account the three modes of heat transfer: conduction, convection, and surface-to-surface radiation. A one-dimensional heat conduction model is applied to tubular daylight device glazing layers. The convective heat transfer from tubular daylight device surfaces to their adjacent air spaces uses existing correlations for natural flows in enclosed air cavities and free stream air spaces. A zonal model, in which the pipe air space is divided into a number of thermally stacked zones, is used to predict the vertical average temperature distribution in the air cavity and wall surface of pipe. Thermal radiation exchange among surfaces uses the formulation of the form factor applied to the aforementioned zonal model. An iterative sequential procedure is proposed to solve the temperature distribution in tubular daylight device glazing layers and air cavities. The U-factor predictions of the simplified model are compared with the National Fenestration Rating Council certified product rating measurement data and detailed computational fluid dynamic simulations. Four tubular daylight device products are simulated under the National Fenestration Rating Council standard rating conditions for the residential (insulation at ceiling level) and commercial (insulation at roof level) settings. The temperatures of the tubular daylight device glazing layers and vertical temperature distribution inside the pipe air space are also compared with the computational fluid dynamic simulations. The results show that the U-factor predictions of the simplified model are in good agreement with the measurement data and computational fluid dynamic simulations, within a maximum deviation of 15% for both the residential and commercial rating conditions. [ABSTRACT FROM PUBLISHER]

Tubular daylighting devices are systems that collect and channel daylight from building roofs into deep interior spaces. To meet high standards of building energy efficiency and glare-free indoor environments, tubular daylighting device technologies have been rapidly and continuously evolving over the past two decades. However, this pace has been counteracted by a lack of reliable computer design tools. This article presents the development of analytical models to compute the optical characteristics (transmittance, reflectance, and layer absorptances) of various types of complex tubular daylighting devices New metrics for the optical and lighting performance are developed. The optical models are based on the ray-tracing technique, and account for the spectral (monochromatic) or broad-band optical properties of tubular daylighting device glazing panes. Experimental validation of these models is presented in an accompanying paper (Laouadi et al., 2013c). [ABSTRACT FROM PUBLISHER]

This article presents the development of a methodology to measure the visible transmittance of complex configurations of tubular daylighting devices under direct sunlight, and conducts a comparison study between the measurements and computer simulations using the new optical model developed in the first part of the study. A large integrating box was built and calibrated, and the procedure was benchmarked by comparing the measurement of a transparent glazing sample with the manufacturer data. Two commercially available tubular daylighting devices with prismatic and frosted elements built into the glazing and a custom-made tubular daylighting device with a complex pipe having roof and ceiling elbows were selected for the comparison study. The model predictions were overall in good agreement with the measurement for the tested tubular daylighting device configurations, and the sources of discrepancies were clearly identified. [ABSTRACT FROM PUBLISHER]

Abstract: Approximately, 20% of the electricity consumed in the world is spent for lighting. More efficient utilization of the sun, as a natural source of light, for lighting would save electricity used for lighting. The aim of this study is to illuminate a windowless room via a light-pipe and dimmable electronic ballasts. Light-pipe is used for the illumination of the space during the daytime. In case of inadequate daylight, artificial lighting is made via dimmable electronic ballasts and fluorescence lamps. Artificial lighting is supervised by a fuzzy logic control system to keep the illumination level at 350lux. When there is a motion in the room, the system works with the message of the motion sensor, which, thereby, enables energy saving. Additionally, dimming the lamps result in conversation of the electrical energy used for illumination. After the experimental studies, 350lux value targeted in the work plane is achieved with ±10lux error. [Copyright &y& Elsevier]

Abstract: This research investigates the design constraints and potential of applying the remote source solar lighting system to the enclosed lift lobbies of high-rise residential buildings in Hong Kong. No natural light is usually provided to these lift lobbies, which depend on electric lighting for illumination. The application of conventional light pipes requires minimum 3m headroom and is not feasible to be applied in the high-rise residential buildings of 2.8m floor height in Hong Kong. A remote source solar lighting system is specifically designed to solve the headroom problem. The daylighting system uses small diameter side-emitting fiber optic as light transmission medium. The factors of solar altitude, solar azimuth angle and solar irradiance are investigated. The shadowing effects caused by neighboring buildings and the supporting framework are analyzed in details. Design parameters of the natural daylight system are defined. Design guidelines and a model design are developed as a reference for building designers in designing a remote source solar lighting system. The design addresses both the functional application as well as the esthetic design. The remote source daylighting system can be integrated into the architectural design of the external facade and lift lobbies. [Copyright &y& Elsevier]

Materials integration in semiconductors, wafer fabrication process development, and device packaging have seemingly evolved at an exponential pace over the last decade. While microprocessor and memory chip manufacturers are the leading drivers of innovation, several other technology sectors benefit from the technologies that enable Moore's law scaling. Image sensor manufacturers, in particular, have realized many advancements from the selective use of advanced wafer fabrication and packaging developments. The motivations for the imaging industry to pursue advanced technology generation scaling are comparable to that of the broader semiconductor industry. In addition, image sensor companies seek a reduction of the camera module form factor, an increase in camera resolution, and an increase in pixel array performance. The pixel size of recent camera phone sensors has shrunk to 1.12 \mum. This is about half the pixel size of leading edge devices of six years prior, and yet mobile imaging sensors have dramatically increased in performance. Design innovation continues to have an increasing contribution to the performance of leading edge pixels; however, to date, it has been fabrication process development that has substantially enabled the continuous breakthroughs in digital imaging. Current image sensor fabrication process flows mark a significant departure from conventional CMOS logic processes. Beyond silicon foundry processes, digital imaging companies must also concern themselves with the optical systems, packaging solutions, and image processing chips required to integrate their silicon devices with the consumer electronics supply chain. Chipworks, as a supplier of competitive intelligence to the semiconductor and electronics industries, monitors the evolution of image sensor technologies as they come into production. Chipworks has obtained charge-coupled devices and CMOS image sensor chips from leading manufacturers and performed structural, compositional, and design analyses to benchmark the successful technologies employed by the market leaders. [ABSTRACT FROM PUBLISHER]

Theoretical and numerical analysis of the transmission function of the focusing system with high numerical aperture was conducted. The purpose of the study was to form a thin light tube in a focal area using the azimuthally polarized radiation. It was analytically shown that, due to destructive interference of two beams formed by two narrow rings, it is possible to overcome not only the full aperture diffraction limit but also the circular aperture limit. In this case, however, the intensity at the center of the focal plane is significantly reduced, which practically leads to the tube rupture. It was numerically shown that long thin one-piece tubes may be formed through the aperture apodization with diffractive axicon phase function or with complex transmission function of Laguerre-Gaussian or Airy-Gaussian beams. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents comparative monitoring of various sized commercial lightpipes at a purposely built test shed with a pitched roof. The purpose of monitoring is to simultaneously compare the performance of lightpipes of different geometries and also to provide data for establishing a formula for performance prediction. The photometric integrating box, which BRE (Building Research Establishment) has adopted as an approximation to the photometric integrating sphere, is employed to determine the lumen output of the lightpipes under real sky condition. This study presents monitoring of four sized lightpipes: straight Φ530mm, elbowed Φ530mm (with a tilted entrance), elbowed Φ450mm and elbowed Φ230mm. A mathematical model is proposed to correlate the measured lumen output, horizontal global illuminance, the diameter and length of the lightpipe, the specular reflectance, solar altitude and azimuth, and orientation of elbow if an elbowed lightpipe is tested. The coefficients in the formula are determined by regression of the monitoring data. The formula is then used to predict the lumen output of a lightpipe from the measured global illuminance for the given geometry and time. The agreement between the measured and predicted lumen output is generally satisfactory. The formula may be a useful design tool as it can predict the lumen output of a lightpipe from the global illuminance value such as those given in EnergyPlus weather data. [Copyright &y& Elsevier]

The article describes an experimental design for gel electrophoresis quantification densitometry using a flatbed optical scanner and lighting from the fluorescent lamp lightpipe in a dismantled liquid crystal display (LCD) computer monitor screen. Topics include the assembly of the apparatus, preparation of a recombinant fusion protein sample, and the gel scanning procedure. It is noted that the apparatus can be used in chemical teaching laboratories without access to a commercial densitometer.

Abstract: The utilization of energy from classical natural sources has some limitations therefore new possibilities for its enhancement are sought. Tubular light guides (TLG) are simple devices that allow the transmission of daylight into interiors of domestic or commercial buildings. The light transmission efficiency (LTE) is important indicator of the light guide performance. It depends on the geometry and optical parameters of the light guide but it seems also on the sky conditions. LTE can be investigated by measurements or calculations. Measurements under a real sky meet with difficulties of sky luminance distribution stability because sun is continually moving and properties of atmosphere are changing. Measurements of the LTE made under the artificial sky with the precisely defined sky luminance distribution can give answer to the question: “Depends the light transmission efficiency of tubular light guides on the sky type determined by the luminance distribution?” It was found that theoretical prediction methods combined with numerical methods could be used to answer this question. In this paper are presented results of theoretical calculations of the tubular light guide transmission efficiency using ray-tracing prediction method compared with measurement results obtained under the artificial sky installed at the Institute of Construction and Architecture of Slovak Academy of Sciences in Bratislava. The main aim of this paper is to offer a method for determination of tubular light guide inner reflectance and mathematically prove that light guide transmission efficiency is different for various standardized overcast sky types. [Copyright &y& Elsevier]

Abstract: Tubular daylight-guidance systems are linear devices that channel daylight into the core of a building. The development, over the last decade, of materials with high specular reflectance has led to a large number of passive zenithal systems; the most commercially successful type of daylight guidance being installed in many parts of the world. The rapid change in technology has not been matched by the development of either reliable and standardised design methods or design criteria against which the systems may be evaluated. This paper presents the results of several surveys of daylight guidance systems in 13 working buildings. These give an indication of the conditions created, which are used as the bases of suggested design criteria. A critical review of existing performance prediction methods notes that these lag far behind comparable methods for electric lighting and conventional glazing. A number of improved methods of prediction, currently under consideration by the CIE Technical Committee TC3-38, are presented and each is tested against measured data from the installation surveys. [Copyright &y& Elsevier]

Abstract: There are now several ways of predicting the illuminance produced for different configurations of light pipe. This study is an overview of two such methods for two slightly different forms of light pipe diffuser. Both models are partly empirical in nature but have been formulated using significantly different techniques. Their outputs are also different in presentation, although both models deal with illuminance predictions (with one of the models offering luminous flux predictions also). The models have also used separately obtained measurements in their formulation and so can be seen as being two independent methods, using similar logic, to achieve similar goals. While the two sets of predictions cannot be compared to each other directly (due to the difference in diffuser in each case), the two models can be presented as an indication as to how modelling procedures of this type can be approached. [Copyright &y& Elsevier]

Abstract: Light pipes are simple means of directing daylight (diffuse and direct light) into interior spaces. Previous work by the authors described the initial work on a luminous flux and illuminance predictive model for straight light pipes, using a basic equation for illuminance distribution as a function of horizontal distance. Further work has now produced a model that uses the cosine law of illuminance to describe the distribution of light from the light pipe diffuser as well as takes into account pipe elbow pieces or bends. The resulting illuminance model can be described as a quartic cosine model. By producing a “luxplot” prediction for any given light pipe application, it is possible to maximise the potential of these daylight providers and design their configuration to suit any given need. As part of this study, wide-ranging illuminance and luminous flux data were collected both for the formulation of this model (as the formula is semi-empirical) and its validation. [Copyright &y& Elsevier]

Daylight represents a free source of illumination of building’s internal spaces. For the right and optimal use of this resource, in addition to the resort to some simple designing expedients that can be brought back to the practice of “building in a workmanlike manner”, it is possible to adopt specific devices able to improve the sunlight captation. Among these devices a class that presents a very interesting compromise between simplicity of realization, costs and daylighting performances is represented by the so-called “light pipes”. Light pipes usually work by means of a device placed on an external closing element which attends to collect, redirect and in some cases, concentrate or collimate the incident luminous flux, and a device situated inside the environments able to transport the daylight inwards the building and distribute it into the deep zone of the rooms so as to obtain a better illuminance distribution. In this work, we propose a light pipe equipped with a flat captation system suitable to be integrated in a building’s facade, without any protrusion as to the architectural envelope.This system includes: a planar closing element, a sunlight’s collecting and deflecting device that optimizes the direction of the incoming solar rays as the solar position varies, a rectilinear duct with optical properties suitable for the transport of the sunlight and for its introduction into the room that has to be illuminated.The daylighting performances are simulated in different conditions of external illuminance and it is done an assessment of the lighting energy savings in a test room simulating a class room. At the end, some considerations and applying indications useful for the designer are presented. [Copyright &y& Elsevier]

A light pipe is an excellent solution to transport and distribute daylight into environments without or with little lighting, guaranteeing comfort inside the rooms. As stated in the literature, the evaluation of the performances of light pipes presents numerous complexities, making the work very difficult for technicians and designers. This study is aimed to present a methodology that is able to identify the potential of light pipes using indices such as daylight autonomy (DA), continuous daylight autonomy (DAc), and useful daylight illuminance (UDI). This paper presents an analysis of daylight obtained by several configurations of simple models of light pipes installed into a 5 × 5 m plant area room. All simulations are carried out in a DAYSIM environment, which allows calculating the annual availability of daylight based on a RADIANCE raytracer backward. Several daylight conditions were analyzed for different light pipe configurations, considering different pipe lengths and a variable number of light pipes. The light pipes are tested also in the horizontal position, for different orientations. The results of all the combinations were compared with the performances of a window with dimensions equal to 1/8 of the internal surface, which was in accordance with the minimum value to be guaranteed by the Italian Regulation (D.M. 5 July 1975 n. 190) for different orientations. The results indicated a difference in daylight distribution, showing a strong correlation between the percentage levels of DA and DAc with the length and number of pipes, during different periods of the year. The simulated model is strongly influenced by the aspect ratio (R = diameter/length). The results show that the illuminance levels decrease drastically, increasing the length. [ABSTRACT FROM AUTHOR]

AlGaN‐based deep ultraviolet light‐emitting diodes (DUV LEDs) are featured with small size, DC driving, no environmental contamination etc., and they are now emerging as the excellent solid‐state light source to replace the conventional mercury based light tubes. Nevertheless, the DUV LEDs are currently affected by the poor external quantum efficiency (EQE), which is caused by the low internal quantum efficiency (IQE) and the very unsatisfying light extraction efficiency (LEE). In this work, the authors disclose the underlying mechanism for the low EQE and summarize the technologies that have been adopted so far for enhancing the EQE. This paper comprehensively reviews III–V nitride based deep ultraviolet light‐emitting diodes (DUV LEDs), which are suffering from the low external quantum efficiency (EQE). This article conducts an in‐depth investigation on the issues that DUV LEDs are encountering now. The strategies that are taken by the research community to improve the EQE are summarized and analyzed. [ABSTRACT FROM AUTHOR]