Annual Probable Sun Hours Extension


Annual Probable Sun Hours (APSH) represents the sunlight that a given window may expect over a year period. APSH is expressed as the percentage of direct sunlight hours divided by number of hours when sky was clear with sun. The sunny hours information is provided by the weather data file.

DL-Light extension APSH

APSH is a measure over a year period. The extension also provides the Winter Probable Sun Hours indicator variant (WPSH) that uses the period from 21st September to 21st March.

APSH is measured on the outside face of the window. If the windows of the model are defined by components, you may need to use the 'Create copy in instances' feature to ensure each window has its own sensor. The default value for the virtual surface offset is set to 1cm for this extension, so the sensor would be 1cm above the surface of the window component. About copy in instances, see page Create virtual surfaces.

APSH of a point on the facade depends on building site weather and environment (relief, obstruction buildings), building shape, facades orientation and sun protections. It is independent on materials used on facades or environment and on building interior.

In UK policies, APSH is often used as a ‘spot’ measure on the mid-point of a window, thus by default this extension uses a 'single sensor in the center', however any kind of sensor grid can be selected.


In UK, policies usually refer to the BRE Handbook ‘Site Planning for Daylight and Sunlight 2011: A Guide to Good Practice, Second Edition’ (2011). The BRE Handbook gives not mandatory guidelines drafted primarily for use with low density suburban developments.

Sunlight is heavily influenced by orientation, north facing windows may receive sunlight on only a handful of occasions in a year, and windows facing eastwards or westwards will only receive sunlight for some parts of the day. Therefore, BRE guidance states that only windows with an orientation within 90 degrees of south need be assessed.

BRE recommends that the APSH received at a given window in the proposed case should be at least 25% of the total available, including at least 5% in winter. Where the proposed values fall short of these, and the loss is greater than 4%, then the proposed values should not be less than 0.8 times their previous value in each period.

How to use APSH Extension

  1. Open SketchUp model. Follow next instructions to prepare your model for DL-Light calculations.

  2. Open APSH dialog from toolbar apsh_dialog_icon or menu Extensions -> De Luminae -> APSH -> Activate extension and enter the parameters of the calculation.

    DL-Light extension sketchup APSH General tab

    Fields description:

  3. Palette of false colours can be defined with precision. 3 options for palette are given, Automatic, Gradient and Custom:

    DL-Light extension sketchup APSH Panel tab
  4. After entering the parameters, select one or few surfaces and press Render or run_selected button.

    DL-Light extension sketchup APSH SketchUp selection

    Calculation time depends on number of selected surfaces and model's complexity.

  5. When results are imported, selected surface will have appropriate false colors and Palette and Report dalogs will be opened.

    DL-Light extension sketchup APSH SketchUp result imported -
            automatic palette
  6. Results analysis.

  7. For further calculations in the same model:

    DL-Light uses a calculation cache algorithm. It automatically detects if a surface requires recalculation or if a previous result can be reused. By default, the cache keeps the information of the last 10 calculations (value configurable in the preferences).

  8. Archiving results:

    DL-Light allows to archive all the results of a calculation: reports, textures and calculation steps (exported Radiance model, weather file, ...). This archive can be reloaded on the model, subject to using exactly the same model as during the calculation.

    See the page Archiving results for more informations about this feature.

    See the page Comparison of results for more informations about comparison of archives.

  9. Snapshots:

    Current SketchUp model view with imported results can be exported with palette snapshot_with_palette_icon or without palette snapshot_icon to png format. Open the folder of images with open_snapshot_folder_icon.
    This option is not supported in trial version of the extension (see licence information).

    DL-Light extension sketchup APSH SketchUp model snapshot image