While there is no doubt daylighting can offer great benefits in terms of energy consumption, sustainability and health, it is also highly sensitive to a careful planning and control. Not only must we try to increase the availability and use of daylight inside buildings, we must also ensure its quality and therefore its energy-efficient and user-responsive control. Any daylighting strategy has to be approached from an integrated perspective, encompassing its potential for illumination, heating and pleasantness and considering its liabilities in terms of glare, thermal discomfort, extra cooling needs and variability. This requires a careful planning based on accurate predictions, for which detailed transmission and reflection data of the fenestration components are essential.