Sun path and shadow diagrams
How the «Sun & shadow» tab computes the sun path and the shadows on the 3D model of the surrounding buildings, what can be set, and how it differs from a daylight and sunlight assessment.
Overview
The «Sun & shadow» tab extrudes the buildings around the site in 3D and shows the sun path and the shadow at the chosen time. A shadow study needs a model of every surrounding building; this tab builds that model and its shadows in the browser, without modelling in Rhino or SketchUp. Use it at concept stage for layout and orientation.
How to use
- Open the «Sun & shadow» tab. If there is no 3D model yet, build it first on the 3D tab
- Choose the date: 21 June (summer solstice), 21 March (spring equinox), 23 September (autumn equinox) or 21 December (winter solstice)
- Set the time with the time slider. The sun position and the shadows follow it
- If needed, turn on «Cast shadows only»
- Fix the view with «North up» or «Plan view» and press «Save PNG»
Settings
| Setting | Value or range | Description |
|---|---|---|
| Date | 21 June · 21 March · 23 September · 21 December | Reference day for the sun path and shadows |
| Time | Greenwich Mean Time (GMT, UTC+0) | Without British Summer Time |
| «Cast shadows only» | On · off | On: face colours stay fixed and only shadows cast by neighbouring buildings show. Off: faces turned away from the sun also darken |
Method
Sun position
Solar altitude and azimuth are computed from latitude, longitude, date and time with the solar position algorithm of the US National
Oceanic and Atmospheric Administration (NOAA). No external service is called. The noon altitude can be checked against
90° − |latitude − solar declination|, with a declination of +23.44° at the summer solstice and −23.44° at the winter solstice.
Values for Bloomsbury (51.52° N), in GMT, computed with the same algorithm:
| Bloomsbury | Sunrise | Solar noon | Noon altitude | Sunset | Theoretical |
|---|---|---|---|---|---|
| Summer solstice 21/6 | 03:43 | 12:02 | 61.9° | 20:22 | 61.9° |
| Spring equinox 21/3 | 06:01 | 12:08 | 38.8° | 18:15 | 38.5° |
| Winter solstice 21/12 | 08:04 | 11:59 | 15.0° | 15:53 | 15.0° |
The equinox altitude differs from the theoretical value because the declination on 21 March 2026 is +0.35°, not exactly 0°. Solar noon moves with the date because of the equation of time (up to about ±16 minutes). London is close to the Greenwich meridian, so the longitude adds only about half a minute.
Time reference
The time is Greenwich Mean Time. British Summer Time is not applied, and the screen labels the time «GMT».
Between the last Sunday of March and the last Sunday of October, add 1 hour to the time shown to get clock time. On 21 June sunrise is shown at 03:43 GMT, which is 04:43 BST on the clock.
Reference dates
| Date | Sun path |
|---|---|
| Summer solstice (21 June) | Highest and longest |
| Equinoxes (21 March · 23 September) | Between the two. The sun rises due east and sets due west |
| Winter solstice (21 December) | Lowest and shortest |
Shading
| Type | State | Test |
|---|---|---|
| Self-shading | The face is turned away from the sun | N·L ≤ 0 |
| Cast shadow | The face looks towards the sun but something blocks it | Facing the sun and occluded |
With both shown, whole buildings turn grey and neighbouring shadows are hard to read. «Cast shadows only» keeps face colours fixed and leaves only the shadows of neighbouring buildings; this suits plates. «North up» rotates the view so north is up without changing tilt or zoom; «Plan view» looks straight down, which is the most accurate view for measuring shadow length.
Limitations
This tab is not a daylight and sunlight assessment. Assessments to the BRE guidance (BR 209) follow their own tests and methods.
The model has no trees, awnings or retaining walls. Heights come from Environment Agency LiDAR flown 2016–2022. Where LiDAR gives less than 2 m (for example on buildings completed after the survey), the height falls back to the OpenStreetMap height, then OpenStreetMap storeys × 3 m, then 3 m. For planning submissions, a model from measured data and a specialist assessment are needed.
Sun hours map
The 3D shadow shows one time of day. The total over a day is on the sun hours map and the SUN HOURS plate.
