Architecture
Daylight Factor Calculator
Rough check of how well-lit a space will feel. DF >= 2% means the space is well-daylit; >= 5% means daylight is dominant.
DF target by use
- Bedroom / corridor: 1% (background daylight, supplemental electric)
- Living room / kitchen: 2-3% (well-daylit)
- Office desk: 2-5% (daylight dominant)
- Classroom / studio: 5%+ (daylight should illuminate without electrics)
- Museum: 1-2% (visibility but UV control critical)
FAQ
What's daylight factor? +
DF = (indoor illuminance / outdoor illuminance) × 100%, under overcast sky. So a DF of 2% means when it's 10,000 lux outside, you have 200 lux inside.
Why average DF? +
Average is a fast metric. For real design you'd compute point-by-point with simulation (Radiance, Diva, ClimateStudio).
Is this LEED-compliant? +
LEED uses spatial Daylight Autonomy (sDA300/50%) from simulation, not DF. DF is older but still useful for quick design checks.