R. M.J. Bokel, C. I. Kranenburg, M. van der Voorden
Delft University of Technology, Faculty of Architecture,

Building Physics Group, PO Box 5043, 2600 Ga Delft, The Netherlands

1. Introduction

Large contrasts within the field of view are very unpleasant to the eye. This phenomenon is called discomfort glare. This discomfort glare is often perceived at the transition between a window and the inside of a facade. There are two possible ways to decrease this type of discomfort glare. The first is switching on an artificial lighting system in the room; the second is the application of some kind of daylighting element at the window. As the first diminishes the potential energy saving which can be reached by using daylight, the focus of our research is the investigation of materials and methods which diminishes the discomfort glare around a window.

The large contrast ratios between the window opening and the inside of the facade in the horizontal direction will not be reduced by using daylighting systems in the upper part of the window plane, which is the focus of most research [1]. A vertical element was therefore developed which decreases the luminance contrast ratio between the window and the inside of the facade [2,3]. At first a semi-circular vertical windowsill of a highly reflecting material was investigated. A more optimal shape, an anidolic shape, was also investigated and was shown to increase the amount of light on the inside of the facade and thus decrease the luminance contrast ratio between the window and the inside of the facade. However, the question remains whether cheaper and simpler methods would not work just as well to reduce the luminance contrast ratios between the window and the facade.