Stanislav Darula

Parametric definition of the daylight climate

Solar radiation and sunlight are the universal and free sources of renewable energy available everywhere and the survival of life and health as well as the conditions of environmental comfort and prosperity are dependent on their effective utilisation.

Daylight Science and Daylighting Technology

Preface.- Introduction.- Short historical review of daylight utilisation by living creatures.- Daylight photometry: history, principles and empirical development.- Propagation of light in the atmospheric environment.- Sky luminance characteristics.- Possibilities to simulate year-round changes of the local daylight climate.- Fundamental principles for daylight calculation methods.- Analytical calculation methods and tools for the design of un-glazed apertures.- Daylight methods and tools to design glazed windows and skylights.- Modelling daylight distribution in complex architectural spaces.- The neurophysiology and psychophysics of visual perception.- Discomfort and disability glare in the visual environment.- Index.

Outdoor Illuminance Levels in the Tropics and their Representation in Virtual Sky Domes

Abstract This paper presents two ways to predict outdoor illuminance levels in the tropics. The first one is based on calculations mainly following the recent CIE/ISO Standard General Sky. The second one applies Virtual Sky Domes (VSD) and Virtual Sky and Sun Domes (VSSD) generated for use with standard light simulation software. The accuracy of the VSD and VSSD methods in predicting illuminance levels with and without sunlight is evaluated and shown to be very close to the calculations. Thus, VSD and VSSD can eventually become useful tools to be added into standard lighting simulation software.

The simultaneous occurrence and relationship of sunlight and skylight under ISO/CIE standard sky types

In daylight science the availability of sunlight and skylight at different times has been studied because of the desire to use daylight in both exterior and interior spaces. Exterior skylight illuminances under overcast skies were adopted as a standard for window design in the past. Current ISO/CIE sky types are standardised as relative luminance patterns normalised to the zenith. In this paper, the zenith luminance in candela/square metre and the resulting diffuse illuminance in lux are determined for all sky types. Furthermore, the proportions of sunlight and skylight under different levels of turbidity are found and documented. Efforts to harmonise electric lighting and daylighting standards need to analyse the data on available daylight in physical units in order to ensure energy savings that respect human requirements as well as providing information suitable for computer-aided design.

Parametrization problems of the very bright cloudy sky conditions

Abstract When exterior global/direct and diffuse illuminance, as well as zenith luminance, is regularly measured and recorded, a selection and specification of the most light efficient skylight conditions is needed. A routine representation of all 1- or 5-minute data on the P–G–D diagram can show extreme diffuse, i.e. skylight ratios normalized to the simultaneous extraterrestrial horizontal illuminance level, which indicate the bright cloudy sky conditions. A new method of cluster analysis was developed to select sky conditions associated with sunlight under specific turbidity or cloudiness conditions at actual solar altitudes, while a rough classification of the sky luminance pattern is possible using the ratio of zenith luminance to diffuse illuminance. Some characteristic data recorded in Bratislava, Slovakia during 1995 and during the three year period 1994–1996, demonstrate the parametrization and selection method used, and document detailed dynamic changes occurring during the brightest days.

A Methodology for Designing and Calibrating an Artificial Sky to Simulate ISO/CIE Sky Types with an Artificial Sun

ABSTRACT Artificial skies are now commonplace in laboratories for daylighting studies in university schools of built environment studies. However, these research and educational devices are often not used to their full potential because they are not calibrated to model even location-specific International Oganisation for Standardisation (ISO)/CIE sky types. Nevertheless, sky luminance patterns and parallel sunbeam produced by an artificial sun in a sky simulator are required for realistic physical modeling. These facilities must be designed and calibrated in well-documented protocols to achieve the scale ratios that proportionally model real outdoor skylight and sunlight conditions. Such exacting tasks can be accomplished by respecting several technical imperatives that this article was written to elaborate and discuss.

The 250th anniversary of daylight science: Looking back and looking forward

This year it is appropriate to celebrate an event of great significance for all illuminating engineers. This year is the 250th anniversary of the publication of major books by Pierre Bouguer and Johann H. Lambert. These books summarise the principles of photometry and of daylight science in particular. It is also an opportunity to mention the basic criteria of daylight design and evaluation still used today, that is the Daylight and Sky Factors together with the methods for the calculation of window solid angles developed by Lambert and several approximations derived later. All 20th Century daylight design tools, for example diagrams, nomograms or protractors are based on these. Although the simplified Daylight or Sky Factors are obsolete now, the solid angle for large area sources with a particular sky luminance specification is still needed for calculating the Daylight Coefficient or absolute illuminance in computer programs.

Applying Solar Geometry to Understand the Foundation Rituals of ‘Old Kingdom’ Egyptian Pyramids

Abstract The republication of the interesting book by Rossi (2003, 2007) has provoked questions about the orientation of Egyptian pyramids from the architectural science point of view. The main concern of this paper is to explain several hypothetical possibilities for orientation of the first step Egyptian pyramid. The oldest monumental step pyramid complex, at Saqqara, was built by Imhotep in the 3rd millennium BC, 3rd Dynasty of the ‘Old Kingdom’. Pre-construction involved a foundation ritual, during which the pyramids south orientation and plan were determined by ‘stretching the cords’, a site design procedure partially illustrated on stone engravings. Though helpful, these illustrations incompletely depict the method of pyramid plan design and orientation. Due to rhombic signs on mastaba foundation stones, some Egyptologists claim that geometry was the primary method used for pyramid plan design and orientation. However, due to the solar equinox festive day and the pharaohs presence at the festival, it is possible that the solar equinox was the day chosen for the ceremony. During the equinox, the gnomon shadow would directly indicate the E-W cardinal points. It is plausible, therefore, that solar geometry, at the equinox, was chosen to establish the primary orientation of the pyramid complex. Sundials based on the equinox sun-shadow were commonly used during the 3rd century BC. This paper discusses methods that could have been available to determine the orientation of pyramids.

Daylighting on the working plane in oriented attic rooms under overcast and clear sky

Abstract The evaluation of daylight conditions in building interiors is based on the Daylight Factor concept after current Slovak standards. Criteria and requirements determined in these standards consider the worst daylight exterior conditions which are described by CIE overcast sky model. The sky luminance distribution of overcast sky is centrical to the zenith, so independence of window orientation to cardinal points is characteristic in daylighting calculations. The sky luminance distribution modelling is one of the main task of the daylight source research more than 50 years. It is evident that also other types of sky conditions exist in nature. An introduction of a new criterion based on photometric variables, which also consider sunlight influence, is expected. This article represents a study of the influence of the interior orientation on distribution of daylighting in attic spaces under an overcast and clear sky

Occurrences of Standard Skies and Luminuos Turbidity Factor in Bratislava

Levels of daylighting in nature continually changing and their daily courses are different day to day. Effectiveness of daylight utilisation in buildings depends on exterior luminous conditions resulting from sunny and sunless situations. Generally, prevailing interiors are illuminated by diffuse skylight during year but sunny orientated rooms can be often exposed by direct sunlight. To describe these conditions the occurrence of sky luminance patterns and light attenuation properties of atmosphere expressed e.g. by luminous turbidity factor are needed. This paper presents the comparison and evaluation of occurrences of ISO/CIE General Standard Sky and luminous turbidity factor in two distant years on the base of measured instantaneous global and diffuse horizontal illuminance, global and diffuse horizontal irradiance and zenith luminance taken during 1995 a 2002 at ICA SAS in Bratislava. The different occurrences of luminous situations described by general standard sky types were found. Results of the luminous turbidity factor calculation show that various atmospheric pollutions during sunny situations can be expected.