Daylight can provide lighting for visual tasks either wholly or in part. Daylight changes its illuminance as well as its spectral composition over the course of the day, and thus creates variability in indoor spaces. Due to a nearly horizontal incidence of light through lateral windows, daylight can create specific modelling and a particular luminance distribution in the room.
Windows can establish visual contact to the outside world, which is preferred by most people. In rooms with lateral windows, however, the daylight level decreases rapidly with increased distance to the windows. In order to ensure the required illuminance at workstations as well as a balanced luminance distribution in the room, additional artificial lighting is necessary. Automatic or manual switching on and/or dimming can be used to achieve a suitable interplay of electrical and natural lighting. To avoid glare through windows, shielding should be provided where appropriate. This applies e.g. for rooms with VDU workstations (see also chapter 1.4.3 "Lighting of offices and rooms with VDU workstations").
The use of daylight and its influence on energy efficiency are described in detail in chapter "Light and ecology".