Overcast Daylight Autonomy
The percentage of occupied time a point meets or beats the target illuminance (typically 300 lx) under an overcast sky, the worst case for daylight.
DAo = 50% → for half the working day no electric light is needed.
A faithful reimplementation of the University of Seville method
Turn a Daylight Factor into overcast daylight autonomy, instantly.
A scientific calculator that turns the static DF into the dynamic DAo and DAo.con metrics: for a single point, a vertical section or a whole floor-plan matrix, with heatmaps and response curves.
Scroll
- 3
- Calculation modes
- 8,320
- Sky samples / point
- 0.000%
- Error vs. reference
Interactive conversion
Fair40.5%autonomy
68.5%continuous
3.00%
Daylight supports part of the occupied time. Computed for latitude 37°, an 08:00–17:00 schedule and a 300 lx target. Everything is adjustable inside the calculator.
01How it works
From Daylight Factor to DAo, step by step
The hard part, simulating a full overcast-sky year, happens in your browser in milliseconds. You only ever supply the Daylight Factor.
- 01
Enter the Daylight Factor
Provide DF at a point, along a vertical section, or across a whole floor-plan grid. DF is a static indicator of a space's daylight performance and, under an overcast sky, it doesn't depend on which way the windows face.
- 02
We model the overcast sky
For every 15-minute step of the occupied year we compute the CIE overcast-sky exterior illuminance from solar geometry, then the interior illuminance as E_int = E_ext × DF/100.
- 03
Read DAo & DAo.con
DAo is the share of occupied time the point meets or beats your lux target; DAo.con also credits partial daylight. Results render as gauges, curves and heatmaps.
02The method
A faithful annual daylight model
This tool reproduces the original University of Seville workbook exactly. The Daylight Factor is orientation-independent, because an overcast sky spreads its light evenly in every direction; DAo, however, does depend on latitude, schedule and the illuminance threshold you set.
Try it nowCIE Standard Overcast Sky · 300 lx default
Solar geometry
δ = asin(0.4 · sin[(d − d₀) · 360 / 365.2422])Solar elevation
γ = asin(sin δ · sin φ + cos δ · cos φ · cos H)Exterior illuminance
Eext = (7/9) · π · (100 + 7580 · sin1.36 γ)Interior illuminance
Eint = Eext · DF / 100DAo / DAo.con
DAo = Σ[ Eint ≥ Et ] / N · DAo.con = ⟨ min(Eint / Et, 1) ⟩γ solar elevation · δ declination · φ latitude · H hour angle · d day of year (d₀ reference) · E_ext exterior light · Eₜ threshold · N occupied steps per year · ⟨·⟩ mean.
03The metrics
Two figures you grasp at a glance
Continuous Overcast Daylight Autonomy
A finer version that also credits partial daylight: a point at 150 lx against a 300 lx target contributes 0.5 instead of being discarded.
DAo.con = 75% → on average, 75% of the target is reached.
Three ways to calculate
From a single DF reading to a full floor-plan heatmap.
Explore
Bring it to your space
Play with room depth and compare design scenarios, all driven by the real calculation engine.
Put numbers on your project's daylight.
Open the calculator and convert your Daylight Factors into DAo and DAo.con. No install, no spreadsheet, visuals straight away.
