Glossary
sDA
Plain-Language Definition
Spatial Daylight Autonomy — the percentage of floor area that receives sufficient daylight (≥300 lux) for at least 50% of annual occupied hours. A metric for evaluating natural lighting quality.
Technical Context
sDA is calculated using annual climate data and building geometry modelling. sDA ≥55% is considered "Preferred" and sDA ≥75% is "Highly Preferred" by IES LM-83. LEED v4.1 awards daylight credits based on sDA. sDA captures both the spatial distribution and temporal consistency of daylight, making it superior to simple daylight factor calculations.
Why It Matters
Good daylighting reduces artificial lighting energy by 30-50% and improves occupant wellbeing, productivity, and circadian rhythm. Studies show employees near windows with good daylight take 6-12% fewer sick days. sDA is increasingly required for WELL and LEED certification.
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