Visual alliesthesia: The gap between comfortable and stimulating illuminance settings Zhonghua Gou a, * , Stephen Siu-Yu Lau b, c , Hai Ye b a Faculty of Built Environment, University of New South Wales, Sydney, Australia b Department of Architecture, Tongji University, China c Department of Architecture, University of Hong Kong, China article info Article history: Received 26 May 2014 Received in revised form 19 July 2014 Accepted 7 August 2014 Available online 16 August 2014 Keywords: Alliesthesia Comfort Stimulation Lighting Productivity Environmental design abstract Based on the theory of “alliesthesia”, there is a gap between how people evaluate an environmental stimulus and how they actually react to the stimulus that changes the state of the interior milieu. Oc- cupants preferred a low illuminance for comfort without or with less stimulation, but the comfortable setting might fail to generate productive environments because comfort is a reference to elimination of discomfort, which assumes that absence of stimulus (such as brightness) is good. A lighting experiment is conducted to identify the gap between comfortable and stimulating illuminance settings. Participants were asked to conduct a visual task and to respond a questionnaire under different illuminances ranging from below 200 Lux to above 900 Lux. The illuminance setting (401e500 Lux) on which subjects felt neutral and most comfortable well complied with current lighting standards. However, the illuminance setting (above 900 Lux) on which subjects scored highly in the visual task and perceived the visual task stimulating was much higher than the most comfortable and neutral setting. As an alternative to pur- suing comfort based on neutrality, this article argues designing stimulating environments with restor- ative elements for productivity and well-being. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Building design has been widely acknowledged as the most cost-effective strategy to increase occupant productivity [1]. This belief leads to numerous lab- or field-based studies to identify comfortable indoor environment settings on temperature, desktop illuminance, etc. [2e5]. In these studies, comfort is defined as the state of mind when subjects express satisfaction with the envi- ronment [6]. The prerequisite for comfort is the absence of envi- ronmental discomfort and a condition in which majority of building occupants do not express dissatisfaction. The comfortable envi- ronmental setting is achieved by neutrality, in other words, main- tenance of neither warm nor cold, neither bright nor dim, etc. [7,8]. However, literature review on thermal comfort found that it would be wrong to assume that neutrality was always the desired thermal sensation [9]. It also disclosed that neutrality was unnecessarily the desired thermal sensation; instead people might prefer other than neutrality [10]. The definition of thermal comfort has been questioned inten- sively, which elicits questions on other environmental design as- pects, such as lighting. The provision of adequate lighting in workplaces is thought as an important contribution to productivity and human well-being. Currently some international standards suggest an illuminance of 500 Lux for normal desk-based office tasksdwriting, typing, reading, data processing [8]. Therefore, 500 Lux is pursued in design practices as an optimum desktop illumi- nance. Occupant surveys [11e 14] confirmed that this standard was a popular setting in today's office environments. People were found to prefer even lower illuminance. In a study that examined the preferred electric light [15], sixty per cent of the participants were satisfied with the desk illuminance between 230 and 730 lux. This study also found that three levels of illuminance from artificial lighting were preferred: less than 250 lux, around 300 lux, and around 500 lux. People chose low artificial light levels when daylight was available, in order to benefit from daylight [11]. Given the choice of artificial light and daylight, most people added no more than 280 lux of artificial light to the daylight available on their desk, even when daylight levels were below 100 lux [16]. * Corresponding author. Faculty of Built Environment, Red Centre West Wing, University of New South Wales, Sydney NSW 2052, Australia. E-mail addresses: gouzhonghua@gmail.com, z.gou@unsw.edu.au (Z. Gou). Contents lists available at ScienceDirect Building and Environment journal homepage: www.elsevier.com/locate/buildenv http://dx.doi.org/10.1016/j.buildenv.2014.08.001 0360-1323/© 2014 Elsevier Ltd. All rights reserved. Building and Environment 82 (2014) 42e49