Artificial Sky Research Articles

Algorithms for calculation of daylight factors in streets

This paper presents algorithms for calculation of sky components and daylight factors in linear building structures using the solid angle projection method. In order to estimate the precision of calculations two sky models; the uniform sky and CIE overcast sky, both giving equal illuminance on the horizontal plane, are used. Daylight factors calculated for CIE overcast sky are also compared to daylight factors measured in a physical scale model of a linear atrium in an artificial sky of the mirror-box type.

Implementing the partial daylight factor method under a scanning sky simulator

Architects need support for the evaluation of the daylighting performance of their buildings. As experimental tools, sky simulators, used in conjunction with scale models, allow a concrete and intuitive approach to the problem. Yet conventional artificial skies and their measurement technology are of limited use, because they are usually not able to evaluate building performance under a non-standard sky luminance distribution (CIE sky models). The Partial Daylight Factor (PDF) method presented in this paper addresses this problem. It is applied to a scanning sky simulator in conjunction with a methodology of experimental research (experimental plans of Hadamard). Scale model experimental simulations carried out with the scanning sky simulator and the PDF method offer an evaluation of the daylighting performance of a building for any luminous configuration of the sky vault. Coupled to a climatic database, they allow an evaluation of daylighting performance indicators such as daylight sufficiency and average or cumulated illuminance for all types of overcast, intermediate and clear skies, including CIE standard models. Moreover, new concepts, such as the Partial Illuminance Factor (PIF), allow a better knowledge and comprehension of the daylighting strategy.

PA—Precision Agriculture: A System for Testing Plastic Film for Bunker Silage Preservation—Design and Preliminary Findings

The connection between the quality of silo sheets and the ensiling process was investigated. For this purpose a test apparatus, which simulates and standardizes the radiation processes at the silo, was developed according to the principle of an ‘artificial sky’. Subsequently, an experiment was carried out with 130 kg portions of wilted grass, each compacted in plastic containers and covered with one of ten different film types, defined by its thickness, colour and structure. The investigation shows that the temperature course in the silage is on similar principle between different film types. Differences between the investigated film types were mainly discovered directly under the film (average temperature, temperature fluctuations, colour of the silage surface). Quantitatively, these differences do not seem to be very important, especially when taking the high standard deviations and the small effects caused in the middle of the containers into consideration. Further experiments are necessary. A test apparatus, such as the ‘artificial sky’, offers a valuable supplement to standard testing methods in silage research.

Naked-eye star visibility and limiting magnitude mapped from DMSP-OLS satellite data

We extend the method introduced by Cinzano et al. to map the artificial sky brightness in large territories from DMSP satellite data, in order to map the naked-eye star visibility and telescopic limiting magnitudes. For these purposes we take into account the altitude of each land area from GTOPO30 world elevation data, the natural sky brightness in the chosen sky direction, based on Garstang modelling, the eye capability with the naked eye or a telescope, based on the Schaefer and Garstang approach, and the stellar extinction in the visual photometric band. For near-zenith sky directions we also take into account screening by terrain elevation. Maps of naked-eye star visibility and telescopic limiting magnitudes are useful for quantifying the capability of the population to perceive our Universe, evaluating the future evolution, making cross-correlations with statistical parameters, and recognizing areas where astronomical observations or popularization can still acceptably be made. We present, as an application, maps of naked-eye star visibility and total sky brightness in the V band in Europe at the zenith with a resolution of approximately 1 km.

Computer Simulation in Daylight Design: A Comparison

Four of the leading computer lighting simulation programs are compared with physical modelling techniques as a means of predicting daylighting of interior spaces. Lightscape (v3-l.l), RadioRay (v2.0), Microstation/J (v7.1Beta) and ADELINE (v2.0NT) are compared with a physical model under two types of artificial sky. The analysis covers three main aspects of operation; physical accuracy of the output, visual quality of the renderings and user interface of the software. With the exception of RadioRay, the software investigated calculates daylight factors within an average of30% of those produced by a physical model. This is within an estimated experimental error of between 25% and 40% depending on location in the room. The visual quality of the output is variable with ADELINE producing the most compelling results. This paper continues to suggest where improvements to the existing technology may lie particularly in reference to interface design.

The Artificial Sky Brightness in Europe Derived from DMSP Satellite Data

We present maps of the artificial sky brightness in Europe in V band with a resolution of ~1 km. The aim is to understand the state of night sky pollution in Europe, to quantify the present situation and to allow future monitoring of trends. For each terrestrial site the artificial sky brightness in a given direction on the sky is obtained by integrating the contributions from each surface area in the surroundings, using detailed models of the propagation in the atmosphere of the upward light flux emitted by the area. The top-of-atmosphere light flux is measured by the Operational Linescan System of the Defence Meteorological Satellite Program (DMSP) satellites. The modelling technique, which was introduced and developed by Garstang, takes into account the extinction along light paths, double scattering of light from atmospheric molecules and aerosols, and Earth curvature. Use of this technique allows us to assess the aerosol content of the atmosphere.

The artificial night sky brightness mapped from DMSP satellite Operational Linescan System measurements

ABSTRA C T We present a method to map the artificial sky brightness across large territories in astronomical photometric bands with a resolution of approximately 1 km. This is of use in quantifying the situation regarding night sky pollution, recognizing potential astronomical sites and allowing future monitoring of trends. The artificial sky brightness present in the chosen direction at a given position on the surface of the Earth is obtained by the integration of the contributions produced by every surface area in the surroundings. Each contribution is computed via detailed models for the propagation in the atmosphere of the upward light flux emitted by the area. The light flux is measured with top-of-atmosphere radiometric observations made by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System. We have applied the described method to Europe, obtaining maps of artificial sky brightness in the V and B bands.

Daylight availability in top-lit atria: prediction of skylight transmittance and daylight factor

Atrium and skylight shapes are important architectural design elements that influence daylight availability within the space and, therefore, lighting energy consumption. There is a lack of prediction models for skylight transmittance. and daylight availability in atria. A new concept was developed to predict the diffuse transmittance of skylights. A skylight shape is converted into a representative shape through a shape parameter. Generic formulae for the skylight diffuse transmittance were developed under different sky conditions. A zonal model combined with the flux transfer method was developed to predict daylight availability in top-lit atria through the predictions of the average daylight factor (DF) at the atrium floor and ceiling (non-glazed portion of the roof), and the local DF normal to walls. The DF model was compared with currently available models derived from theory and experiments under artificial skies. The results showed that the computed e transmittance for translucent skylights. under r...

Parallax in artificial sky domes

Matt artificial sky domes are prone to parallax errors because the luminance of each element of the sky is independent of the viewing direction. Since the luminance of a real sky varies with the viewing direction, the luminance distribution of a non-uniform matt sky cannot be correct for more than one viewpoint. Unfortunately, a model building has to comprise a variety of viewpoints. Parallax errors can be eliminated if the luminance of each element of the sky dome is permitted to vary appropriately with viewing direction. Implementation, advantages and limitations of this arrangement are discussed.

LIGHT WELLS IN RESIDENTIAL BUILDING AS A COMPLEMENTARY DAYLIGHT SOURCE

This paper presents the results of the illumination measurements and analyses, carried out on the scale model of an energy conscious multi-storey apartment building using light wells as an additional source of daylight. The design of the building is based on a compact longitudinal structure consisting of east or west oriented flats with only one outer wall and a deep ground-plan. To additionally daylight the central areas of the building and at the same time to control the heat gains and losses, three types of innovative light-guiding systems with several variations were devised. The illuminance measurements on the scale models were carried out under an artificial sky. The measurements showed that the best results were obtained by using light well with wide upper and narrow lower part into which the reflecting wall was placed. In all the cases the reference values were reached.

Reflectance distributions and atrium daylight levels: a model study

In this study parametric changes were made to the distribution of reflectances of diffuse surfaces in the well of a square atrium model that was placed inside an artificial sky. The effects of thes...

Artificial light and sun compass orientation in the sandhopper Talitrus saltator (Crustacea, Amphipoda)

Experiments on compass orientation under artificial light were conducted with adult individuals of Talitrus saltator. The aim was to reproduce in the laboratory an orientation based on the sun compass corresponding to that recorded in conditions of the true sun and sky. This was obtained by the creation within an opaque Plexiglas dome of a scenario that permitted variation of the brightness of the artificial sky and sun. The results show that it is possible to obtain sun compass orientation corresponding to the natural situation even in an artificial environment. It can be concluded that sandhoppers identify an artificial light source as the sun if the artificial sky is also illuminated and if the intensities of the artificial sun and sky exceed certain threshold values (1.13 and 10 μW cm−2, respectively). The results of other experiments under the natural blue sky with an artificial sun and with the real sun attenuated are discussed.

Mathematical and Physical Simulation of Indoor Daylighting: A Case Study

Modern lighting technology aims at the developing of energy efficient lighting system, that is, the objective is to provide good visual environment to the occupants as well as to conserve energy by consuming minimum electricity. With the increasing electricity cost there is a renewed interest of the use of daylight.A fair scope of energy conservation is also available by proper utilisation of daylight. The variable nature of daylight makes the daylighting design a complex one. Hence during design stage of a building-project both quantitative and qualitative evaluation of daylighting performance within interior is essential. In this paper, the total glazing area for an office room was calculated for required area-weighted average illuminance recommended by Bureau of Indian Standard using BRE window design formula. The daylighting performance of the room was studied by Mathematical and Physical simulation. The Mathematical simulation was done using CIE Standard overcast sky and Indian clear sky. The physical simulation was carried out under Artificial Sky setup at Illumination Eng. Section of the E.E. Department which can produce sky luminance distribution pattern very close to that of the CIE Overcast sky. The experimental and theoretical results were discussed.

Investigations for improving the daylighting potential of double-skinned office buildings

This study looks at the daylighting implications of several options for the refurbishment of an existing office building in Brussels, with a perimeter ceiling height of 2.5 m and a width of 16 m. Each side has a double-skinned facade, with a 1.4 m wide maintenance walkway in the space between the internal and external glazing. Scale models in an artificial sky, and computer simulations, were used to examine the effects of changes to the walkway. Two changes in the building's form were also examined, re-entrant slots in the facade, and lowering of the central area of floor. The results from these experiments are generally applicable to buildings designed with double-skinned facades, buildings using horizontal solar shading devices, light shelves or buildings with low floor to ceiling heights. If an area of the floor space is considered to be daylit when it receives at least 300 Lux for over 50% of the working year, it was found that using the walkway options alone, the daylit area can be increased by up to 23%. Re-entrant façade slots produced no increase in the daylit area. Lowering the central floor area produced an increase of up to 14%. None of the walkway options were able to produce a daylit area of greater than 53% of the total floor space. Thus, until redirecting glazing becomes commercially viable, it is clear that shallowplan designs are the best option for new buildings. The RADIANCE computer modelling package was used in addition to scale-model measurements. The use of both of these methods of daylighting analysis is compared. The results of both methods show good agreement.

新しい直接照射型人工天空の開発

Daylighting is fundamental and essential in constructing a comfortable interior environment in architectural space.Research work on daylight and daylighting designs are often carried out applying scale models which is an important technique for the prediction of daylit interior spaces.Artificial skies can be used to reproduce sky luminance distribution through artificial light sources. They are the most effective and useful in the evaluation of daylit environments with scale models. As a result, a number of artificial skies have been constructed at various research organizations throughout the world in the last half a century.A new artificial sky was intended to be developed and constructed by the authors. The artificial skies already constructed throughout the world are being surveyed, for the planning of the new facility. These artificial skies can be roughly classified into four categories as follows: 1. Mirror type, 2. Reflection type, 3. Translucent type, and 4. Direct type.After a survey and comparison of the performance of these types of artificial skies, the concept of a new artificial sky will be established.

人工天空システムによる昼光シミュレーション実験

人工天空システムによる昼光シミュレーション実験

人工天空システムによる昼光シミュレーション実験

人工天空システムによる昼光シミュレーション実験

人工天空システムによる昼光シミュレーション実験

人工天空システムによる昼光シミュレーション実験

Study on the Prediction of Illuminance by Daylight in a Retractable Domed Stadium.

A daylighting calculation method for a domed stadium is presented. Based on this method, a computer program has been developed to predict illuminance distribution by daylight in a retractable domed stadium. Direct sunlight and skylight are considered as the daylighting sources in this program. Skylight model is based on the C.I.E. (Commission Internationale de l’Eclairage) Overcast and Clear Sky functions. For the purpose of examine the accuracy of the prediction by the computer program, the calculations were compared with the scale model measurements. A retractable domed stadium was designed and the 1:200 scale model was made. Illuminance measurements were carried out by setting the scale model under an artificial sky. The measured values were compared with the predicted values for the same conditions simulated by the computer program. As for this stadium, the predicted values agreed well with the measured values.

直接照射型人工天空の輝度分布校正について

直接照射型人工天空の輝度分布校正について