Sunlight and the monochrome linear relief

Abstract

The paper focuses on the visual impression of a modern linear relief illuminated by sunlight. It starts with the reference to the ancient stone reliefs from Egypt and Persia and discusses the typology of stone relief: sunk, mid and high relief. Then modern Norwegian architectural examples of wall relief are shown, including the oak wall in the Opera House in Oslo and works of contemporary fine artist Edith Lundebrekke. The method of developing modern reliefs is totally different, most often it is based on the fastening of wooden slats to the wall and consequently the relief shape is dominated by linear elements that may differ in regard to thickness, width, length and colour. A series of parameters influencing perception of modern linear reliefs have been examined with the help of calculations of the sunlit part of a relief and with visual studies of previously prepared coloured relief plates that were illuminated by an artificial sun in the Daylight Laboratory at the Norwegian University of Science and Technology (NTNU), Light & Colour Group. The common opinion saying that the lightness (perceived luminance) of a relief depends mostly on its depth has been challenged. The depth is of course very important, but for observation angles close to the incidence angle of the sunlight the relief lightness is high even for very deep reliefs and for angles opposite to it the only essential parameter is the relation between the widths of the outer and the inner surfaces. The main conclusion is that in addition to the design of the relief itself, i.e., its colour and the widths of the inner, outer and side surfaces, there is a combination of the light direction and the observation direction that decides how much of the relief image (as seen from the observer) is illuminated by the sun and consequently how light the relief appears.