Analysis Parameters
15°
Daylight Availability Calendar
Night (sun below horizon)
Low-angle (0° – 15°)
Useful (15° – 45°)
High-angle (> 45°)
Annual Daylight Summary
Seasonal Pattern
Available daylight peaks in June and bottoms in December — a geometric inevitability of latitude. Useful daylight follows the same curve but never quite as much, with the low-angle margin biggest in summer (long shoulder hours) and smallest in winter (shorter days, but more compressed sun arc).
Method: Solar altitude is computed at the midpoint of each hour using
the standard NOAA equations (declination from day-of-year, equation of time, hour angle
with longitude correction relative to the local standard time meridian). A grid cell is
classified as night if the sun is at or below the horizon; low-angle
if altitude is between 0° and the threshold; useful if above the threshold up
to 45°; and high-angle above 45°. The default 15° threshold reflects the
conventional daylighting heuristic: below this altitude, exterior illuminance drops
sharply (air mass > 4), the beam is nearly horizontal (severe glare on east/west
facades), and the cosine factor on horizontal workplanes is < 0.26. Monthly totals
use the representative day (15th) of each month scaled by days in month.
What this is — and what it isn't: This tool answers a purely geometric question: of the hours the sun is in the sky, how many deliver meaningfully useful daylight to a building? It does not account for sky cover (cloudy vs. clear), interior workplane illuminance (which depends on glazing, geometry, and obstructions), or visual comfort metrics like UDI on the workplane. It complements rather than replaces those analyses.
What this is — and what it isn't: This tool answers a purely geometric question: of the hours the sun is in the sky, how many deliver meaningfully useful daylight to a building? It does not account for sky cover (cloudy vs. clear), interior workplane illuminance (which depends on glazing, geometry, and obstructions), or visual comfort metrics like UDI on the workplane. It complements rather than replaces those analyses.