Search

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]

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]

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]

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]

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 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]

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: 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]