Surprising results from a Post Occupancy Evaluation of the way internal roller blinds impact perceptions of visual discomfort

Blinds and shutters are one of the few products in the built environment that affect perceptions of visual and thermal comfort. However, in general, internal roller blinds are more frequently installed in UK offices to improve visual comfort as opposed to thermal comfort. With the increased frequency in warmer weather events resulting from climate change it is likely that blinds will be extended more frequently to improve thermal comfort as well as reducing perceptions of glare and visual strain. When internal shading products are extended it is assumed that glare and visual strain will no longer be experienced. However, when conducting a Post Occupancy Evaluation (POE) into whether the position of roller blinds (either fully extended or fully open) affected perceptions of glare, a greater level of visual discomfort (specifically glare) was experienced by occupants when shading products were closed. Distributions of light around the task area play an important role in improving visual comfort when occupants are carrying out desk-based activities yet moveable shading is frequently excluded from daylight simulation assessments of visual comfort. The closure of blinds can affect the distribution of daylight within a space and thus occupants can perceive glare issues from other internal sources of light. This research suggests that the deployment of shading products should be considered in the assessment and predictions of internal lighting conditions to provide lighting designers with a more holistic view of visual comfort throughout the year. Furthermore, in POE it would be beneficial to ask occupants what they believe the glare source to be.