Daylight Glare: a review of discomfort indexes

Daylight, in interior lighting design, is more and more frequent, not just for physiological and psychological causes, but also for energy saving that could be obtained through a suitable daylighting and an optimal integration between daylight and electrical light. Also the new European standard EN 15193 (2007), “Energy performance of buildings – energy requirements”, about energy saving in buildings, considers the lighting system as a relevant element for building energy performance evaluation. The advantages related to daylight presence into the working areas make this illumination system the favourite one by designers and engineers. However, glare is often inter-related to daylighting and is generated by: High level of lighting from direct solar radiation or from sky vault (when any part of it is in the observer field of view); Secondary reflection of light from internal and external surfaces, characterized by high reflection factor. In this paper, after a brief description concerning glare phenomena, it is made evidence of the uncertainty and complexity of DGI applications. Furthermore, the main glare indexes in the current technical literature are analysed, making a comparison analysis of the measurement methods of the parameters and of the equations used for calculation.