Views on ancient lighting: Modelling lighting devices and their effects in architecture
Creators: name: Grobe, Lars Oliver
name: Noback, Andreas
name: Bielfeldt, Ruth
name: Henkelmann, Vera
name: Lang, Franziska
Publisher: name: Zenodo
Year: 2021
Subjects: lighting simulation
luminaire modelling
lychnology

description: Artificial lighting and daylighting as methods to deliberately bring light into the dark respond to the design and use of architecture. If these are altered or lost, our knowledge about the history of that practice is inferred from archaeological evidence of preserved lighting devices, indications for window openings sometimes accompanied by finds of glass panes, and other sources such as texts and illustrations. From this fragmented knowledge the effects of lighting, which often results from the combined utilisation of daylight and other lighting devices, can be reconstructed employing computational simulation (Noback et al, 2020). Pre-modern lighting devices, or luminaires, such as torches, open fires, candles, and oil lamps (Garnett et al., 2019), almost exclusively rely on flames as light sources. Modelling light emission of such flames can be based on an analytical representation of the combustion processes, or phe- nomenological approaches e. g. data acquired from photometric measurements. The luminaire is illuminated by the initial, approximately uniform emission of light from the flame. Mirror-like sur- faces or diffractive solids, e. g. reflecting metal disks or glass lamps filled with clear fuels, can modulate the flame light and form complex distributions (Kider et al., 2009). If based on valid geometric models of the luminaires, simulation produces descriptions of lighting in terms of physical quantit- ies: imagery representing luminance distributions in the field of view, or tabular data, e. g. illuminance distributions on defined surfaces. Based on these, metrics and models of human visual response allow to analyse effects of lighting on architectural spaces and features (Doulos et al., 2019). These can be functional, e. g. the provision of illuminance for visual tasks, or perceptual, e. g. on the appearance of space and surfaces (Noback et al., 2020) or the luminaires themselves. A plentitude of approaches exist in computer graphics to model flames and their visual effects by flames. These techniques often focus on the dynamics of flames, e. g. by particle systems, but do hardly aim at physical validity. Physically valid luminaire modelling that is applicable in lighting simulation of architectural spaces with potentially many light sources has to maintain validity but hide the complexity of internal processes in the flame. This paper presents a method for the study of lighting and perception based on modelling luminaires and their effects on the illumination of architectural spaces with the lighting simulation suite Radiance. In the presented, preliminary phase, the model of the flame is static, i. e. not accounting for movement, flicker and intensity changes. The applicability of the method to selected cases of lighting devices and preliminary results shall discussed, leading to an outlook into the authors’ ongoing and future research activities in the field.