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eng.daylight-factor Calculator
Calculates the daylight factor (interior illuminance / exterior illuminance × 100%) for a room from window area, glazing transmittance, and room dimensions. Daylight factor above 2% provides adequate natural lighting for office tasks — UK building regulations consider this adequate for working areas.
Inputs
Ew Lux
Reference formula or conversion factor shown for context.
Ei Lux
Reference formula or conversion factor shown for context.
Window Area M2
Two-dimensional surface extent (m²). For complex shapes, break into simpler sub-shapes and sum.
Floor Area M2
Two-dimensional surface extent (m²). For complex shapes, break into simpler sub-shapes and sum.
Results
daylight factor DF (%)
A dimensionless multiplier applied in the calculation.
window-to-floor area ratio (WWR)
The proportional relationship between two quantities.
expected DF from WWR (rough)
Reference formula or conversion factor shown for context.
DF = (Ei/Ew) × 100%
Reference formula or conversion factor shown for context.
BREEAM targets
Reference formula or conversion factor shown for context.