Office buildings in regions with abundant sunlight may still fail to make effective use of daylight: the difficulty in controlling variations in natural illumination, which may be substantial, often results in extensive use of artificial lighting. A solution to this paradox was sought by means of a controlled experiment designed to investigate the effect of several strategies to reduce glare and to achieve visual comfort in a test room configured to represent a typical side-lit office. Subjects performed office tasks such as reading or operating a computer, and completed a detailed questionnaire about their work environment, whose physical parameters were monitored in great detail. The study showed that if the window is exposed to direct sunlight, the use of tinted glass may not be an adequate response. Internal Venetian blinds, if deployed correctly, may prevent glare and provide visual comfort to workers near the window - but they require frequent adjustment and reduce the depth at which daylighting may still be enjoyed. A light shelf with an exterior part to shade the view pane from direct sunlight in summer and an interior part to reflect light to the ceiling resulted in superior daylighting and better visual comfort in all room configurations. It is suggested that since windows in offices fulfil multiple roles (daylighting, natural ventilation and a view outdoors), their functioning could be improved by subdividing them into panes to optimize their provision.