Design Solution · Lighting
Design Solution · Dream about it
Optimise average daylight factor to balance natural light against solar gain.
Average daylight factor is computed across floorplates and used as an optimisation target so glazing ratio, shading and layout deliver good natural light without excess solar gain. Better daylight cuts electric lighting energy and improves occupant wellbeing.
Average daylight factor has been the standard daylight metric in UK building regulation and schools design guides for decades, so using it as an optimisation target is methodologically settled rather than innovative — the value here is in the discipline of making the calculation drive facade and layout decisions rather than arriving post-design as a compliance check. The practical benefit is real: good daylight factor distribution reduces electric lighting hours and improves occupant wellbeing and cognitive performance, and the optimisation trade-off against solar gain is a design problem with well-tested solutions in shading, glazing specification and orientation. The limitation is increasingly acknowledged in current guidance: average daylight factor is a sky-only metric that ignores sun position, surrounding obstructions and internal reflectance variation, and it can be satisfied by designs that deliver poor spatial daylight distribution despite an acceptable average. CIBSE LG10 and the newer spatial daylight autonomy metrics offer more discrimination for occupied space quality, and BREEAM Hea 01 has moved toward illuminance-based metrics. A specifier running this as a sole daylight strategy on a dense urban site risks meeting the metric while producing poor daylit environments; complement it with point-in-time and annual climate-based metrics before fixing glazing and shading strategy.
#daylight #ADF #facade #wellbeing