As for now, it seems to be infeasible to predict or measure the perceived degree of discomfort glare from windows. Within an international research project between Delft University of Technology and Berlin University of Technology, user acceptance studies are carried out in full-scale rooms under real sky conditions to study discomfort glare in daylit situations. The aim of the studies was to draw up a relation between glare assessments and measured quantities. For this purpose two test rooms are used: one room was occupied by the subject. in the other one the required measuring equipment was placed, An electronic questionnaire was developed for these studies and installed on the computer of the subject. Continuous measurements were necessary, to link subjective assessments to measured quantities that are obtained concurrently. The obtained relation can be used to predict the average visual comfort evaluation under specific lighting conditions and to propose visual comfort criteria to maintain visual comfort. The study showed that the vertical illuminance measured near the facade and the average sky I luminance measured from the back of the room are good measures to monitor visual comfort under intermediate and overcast sky conditions. The visual comfort criteria should nonetheless be used with care, since the diversity of individual preferences is large. The user preferably has an user inter-face to overrule the glare protection when it is controlled on these visual comfort criteria. (C) 2002 Elsevier Science Ltd. All rights reserved.