Lighting calculations involving iteration or repetition present a problem of interest for many lighting tasks. Repeated calculation is needed, for example, in a design process for the best design evaluation or when a lighting system performance simulation is required A fast solution of the repeated calculation problem can be of special value for the computer-aided design of a lighting system. This paper discusses how the problem of repeated lighting calculations could be handled by the LU decomposition method. This method is commonly used by numerical mathematics for the solution of a single system of linear equations Ax = b, when there is more than one light-hand side b. To speed up the process of repeated solutions, the method involves decomposing a matrix A into an equivalent pair L and U, where L and U are lower and upper triangular matrices, respectively. The proposed LU decomposition method is compared with the traditional solution methods and its performance is shown. Examples of its use are presented to illustrate a possible field for the application of the method.

Glare from very small sources is grossly overrated by the UGR (Unified Glare Rating) formula. Experiments were carried out on glare from small sources at interior lighting distances. Results varied widely but were of adequate statistical accuracy. They showed that a small glare source is characterised by a constant projected area of 0.005 m2, not a constant solid angle; that glare from a source below 0.005 m2 is determined by its intensity, not by its luminance; and that the UGR formula is applicable to small sources if it is suitable modified (L2ω becomes 200I 2/R2).

This paper complements the data presented in phase I of this study. This paper looks at three new escape lighting systems, and compares them with three systems tested previously. In addition to testing their suitability for 30 people with different visual impairments, results are presented for 12 normally sighted people. Using the facilities at the Building Research Establishment, it has been possible to examine the performance of ceiling-mounted emergency luminaires providing two levels of illuminance, LED strips in two configurations, LED strips with overhead luminaires and miniature incandescent wayfinding strips. Speeds of movement are presented here, along with subjective responses. Comparisons are made with findings from normally sighted people. There are no significant differences in the walking speeds under the lighting systems, but the visually impaired subjects had significantly different opinions on the ease with which they could see where to go.

This paper examines the relationship between the physical parameters of a lit environment and visual comfort, as expressed by visual performance, pleasantness and satisfaction, through the comparison of three systems with different light distributions and uplight percentages in an experimental study in a real office. This relationship was evaluated both by measurement of the physical quantities and from subjective responses to the lit environment.

The method presented in this paper is a practical procedure, which can be easily implemented in computer software, for the derivation of illuminances on the surfaces of urban canyons with balconies in sunlit areas, permitting the designer to explore a series of possibilities. The development of the method is based on the division of an urban canyon into a series of structural elements connected to each other for the purpose of illuminance calculations by flux transfer equations.

The merits and limitations of the unified glare rating (UGR) system are discussed, especially the significance of proportionality with the size of the glare source which assures a rational application to multiple-source installations. The compatibility flf recent glare research with the UGR is analysed.

The paper provides a method for measuring the emission time for the voltage-controlled preheating mode of a fluorescent lamp cathode. The method is based on monitoring the lamp voltage. The paper presents the difference between the thermionic emission curves obtained by the method based on the ratio of hot to cold coil resistance (Rh/Rc ) and by the lamp voltage monitoring method. It is supposed that the Rh /Rc method curve is mainly influenced by the heterogeneous cathode heating. The cathode is composed of the filament coil and the emissive material, the specific heat capacities of which differ. It is believed that this difference makes it difficult to create a thermal balance in the whole cathode when the emissive coating reaches the emission temperature at a time soon after the initial current surge. This makes it difficult to describe the thermionic emission characteristics dynamically by the Rh/R c method. An equation is proposed for the thermionic emission curve provided by the lamp voltage monitoring method. Energy supplied to the cathodes until the emission time is reached is examined in terms of the average resistance of the cathode.

The performance of a luminaire with twin fluorescent lamps and a louvre is modelled. The surface reflectance and the size of louvre have a large influence on both the luminaire efficiency and restriction. It is shown that surfaces reflecting vertically would increase glare. Although the luminaire efficiency decreases with increasing louvre depth, the glare may be restricted in the vertical and parallel directions. As the cell pitch of the louvre decreases, the in the corresponding direction decreases in direct proportion, as does the luminaire efficiency.