These systems sequentially turn off lights floor by floor or the entire building. Although not necessarily a control system, manually turning off lights when not in use can result in significant energy savings. This strategy uses the light from clear sky or overcast sky as an interior light source. Daylighting is more common in commercial operations where building use coincides with natural availability. Partly cloudy skies often produce the highest level of illumination.
Overcast skies produce the most uniform levels of illumination.
Daylight penetration is 2.5x the head height. Daylighting is accomplished through the strategic use of windows, light shelves, clerestoreys and skylights. However, the benefit of skylights can be offset by the reduced insulation value in the ceiling. Further, the use of windows can result in solar gains that may require additional cooling thereby offsetting the benefits. It is recommended that computer modeling be performed to see if there are energy benefits associated with the use of a daylighting strategy.