Richard Kittler

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.

Daylight measurement data: Methods of evaluation and representation

The International Daylight Measurement Programme will generate a large amount of data from distinct locations worldwide. To ensure comparability of results, data must be identified uniquely and standardisation of data analysis including the determination of derived quantities is necessary. A number of formulae are proposed for the normalisation and analysis of direct beam, global and diffuse irradiances and illuminances and sky luminance distributions. Graphical representation of results is discussed and a graphical approach, the P-G-D diagram, is put forward as a solution for irradiance and illuminance data presentation.

RADIANCE DISTRIBUTION ON DENSELY OVERCAST SKIES: COMPARISON WITH CIE LUMINANCE STANDARD

Abstract In this contribution some data measured in Europe are evaluated to enable the comparison of real radiance distributions with the CIE (International Commission on Illumination) luminance gradation approximation of the densely overcast sky. A question is posed whether such a model sky exists in reality, although the frequency of its occurrence might be different in different seasons and in regions with different climates. Eleven cases are evaluated in Figs. 1–3 with the comparison to the cosine and the exponential approximation curves. It seems that the measurement data agree with the CIE Standard but further tests and results obtained during the International Daylight Measurement Programme have to gather more evidence.

Some qualities of scattering functions defining sky radiance distributions

The construction of empirical sky models necessary for the diffuse/sky irradiance calculations can respect theory and reality better when presuming the primary functional influences of the gradation and scattering redistribution of solar radiation within the atmosphere. The multiple scattering/diffusion and reflection caused by tiny particles of the, more or less, turbid atmosphere form the sky pattern which can be characterized by a radiance/luminance solid or its section, the scattering indicatrix. Model approximations of indicatrix functions are analyzed by using theoretical considerations or by deriving indicatrices from measured radiance sky scans. Advantages of applying the scattering indicatrix concept are documented by the comparison of measured, modelled, and calculated indicatrix courses.

Universal Modelling of Daylight Climates for Design Purposes

Progressive needs of energy conscious design presume a realistic simulation of unsteady-state daylight situations linking skylight with sunlight during sunny periods. Typical momentary sky patterns have been suggested for standardisation based on an universal parametrisation system that allows the predetermination of the effective sky luminance distribution as well as the resulting diffuse skylight and direct sunlight illuminance either in absolute units or in ratios normalised to the extraterrestrial input. This universal system of modelling formulae and parameters is concisely described in this paper with the stress on its world-wide validity and applicability.

Relative scattering indicatrix: Derivation from regular radiance/luminance distribution sky scans

The diffusion/ scattering indicatrix is a section. (enveloping curve) of the luminance solid indicating the relative amount of sunlight (of the originally parallel extraterrestrial ray) scattered or spread in various directions from a typical atmospheric aerosol particle. Since such luminance solids are usually rc~ta.tiaz~a~iy symmetrical about the sun ray, the scattering indicatrix characterises in luminance terms the redirection,/ redistribution of sunlight due to a turbid medium.

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.