Identical visual task areas close to windows and at room depth

Figure 2.79:

Distribution of horizontal daylight illuminance Ep in a classroom

If identical visual task areas in a room are not provided with equal amounts of daylight, it is possible to use the least supplied area for reference regarding daylight-dependent regulation in terms of standard-compliant light supply of all working areas or to differentiate and divide the room up into several regulation areas within which daylight supply can be described as nearly equivalent.

In individual cases, insufficient daylight supply in partial areas can be balanced out via positive offset, meaning elevated levels of artificial lighting. An installation of this type often saves costs compared to the implementation of additional, independent regulation. However, this possibility must be evaluated critically.

In many rooms, daylight supply along window walls is nearly equivalent while varying strongly towards room depth, which is described in photometrics by using the so-called daylight factor (see figure, see also chapter 1.3.5.6). At lintel heights of up to 3 metres, it is safe to assume that e.g. at 5 metres of room depth, less than a third of the average illuminance related to the overall area applies at the working plane at 0.8 metres height. Offset regulation would not be an expedient solution for this ratio. Instead, a provision of permanent 100% operation should be evaluated here.

Figure 2.80: Daylight-dependent regulation in several identical visual task areas

Where luminaire groups in a room are intended to be regulated independently, interfering impacts of luminaire groups among each other must be avoided. To this end, it is recommended to evaluate manufacturers’ notes regarding possible, documented system configurations (see figure). In some cases, parallel operation of several individual systems in adjacent areas in particular can lead to significant malfunctions, which are nearly impossible to master for users, who generally are not experts.

Example for a malfunction: Two parallel systems are connected to a joint on/off push-button. With sufficient daylight supply, the group close to the window switches off, while the group at room depth remains active. Operating the push-button leads to unintended toggle operation (groups alternating between on and off).