Location
Room & window
Outside the window
Opposite buildings, a garden wall or trees. A house across a narrow street typically blocks 25–40°.
Room sunlight simulator
Set the direction your window faces and watch where the sun actually lands on the floor — hour by hour, and month by month.
Floor plan
Direct sun hours by month
Clear-sky maximum — cloud will reduce thisWhen the sun reaches this room
| Month | First direct sun | Last direct sun | Hours of direct sun | Deepest reach into room |
|---|
"Deepest reach" is how far the sunlit patch extends from the window wall at its furthest, on the 15th of that month.
What the simulation does and doesn't include
The sunlit patch is a true projection: every corner of the window is traced along the real sun direction onto the floor plane, then clipped to the room. What it leaves out is glazing bars, deep window reveals, curtains, and light bouncing off walls — all of which soften the edges in reality. It also assumes a clear sky, so treat the hours as an upper bound for a cloudless day rather than an average.
Common questions
How do I find which way my window faces?
Three ways, in ascending order of reliability: a phone compass held flat while you look out of the window; a north-up satellite map, reading the angle of the wall the window sits in; or the sun itself, by noting the time the sun shines squarely through the opening and comparing that against the sun's known bearing at that moment. The last is the most accurate because it ignores magnetic interference and uses true north.
Why does the sunlit patch move so quickly in the evening?
Because the sun's bearing changes fastest when it is low. Near midday the sun is high and its compass direction barely shifts, so the patch of light creeps. Within an hour or two of sunset the bearing swings quickly and the sun's altitude drops, which stretches the beam and slides it rapidly across the floor. That is also why evening light feels like it changes minute by minute while midday light does not.
What counts as a good number of sun hours?
It depends entirely on what the room is for. A bedroom rarely benefits from long afternoon sun; a living room used in the evening does. As a rough guide, four or more hours of direct sun makes a room feel bright and warm in summer and risks overheating without shading, while under an hour gives the even, cool light that suits screens and studios. The monthly chart matters more than any single day.
Does this account for curtains, glazing bars or deep reveals?
No. The patch is a clean projection of the window opening, so real edges will be softer and slightly smaller. Deep reveals in thick walls cut low-angle sun noticeably, glazing bars break the patch into sections, and light bouncing off walls and floors spreads illumination well beyond the direct patch. Treat the shape as the direct beam only.
My room has more than one window — what then?
Run it once per window and add the results, remembering that the hours may overlap rather than sum. A room with east and west windows gets morning sun through one and evening sun through the other, so its total sunlit hours are close to the sum; a room with two windows in the same wall gains area but not hours.