Vertical Sky Component Extension


Vertical Sky Component (VSC) is a measure of the amount of sky visible from a given point. It is expressed as a percentage. It is the ratio of the illuminance at a given point due to the light received directly from an overcast sky to the illuminance on an unobstructed outside plane under the same sky (CIE standard overcast sky).

DL-Light extension VSC

VSC 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 in front of the surface of the window component. About copy in instances, see page Create virtual surfaces.

In UK policies, VSC is a ‘spot’ measure of the skylight reaching 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.


The use of vertical daylight metrics is still not widely acknowledged, and the VSC seems to be used mainly in United Kingdom, Hong Kong and Sweden. Policies uning VSC usually also use other indicators like APSH.

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.

The maximum percentage value for a vertical window with a completely unobstructed view through 90° in every direction is about 39.6%. In order to maintain good levels of daylight the BRE guidance recommend that the VSC of a window should be 27% or greater.
However, the 2011 BRE handbook makes allowance for different target values in cases where a higher degree of obstruction may be unavoidable such as historic city centres or modern high rise buildings. The guide states that the 27% value is:
"...purely advisory and different targets may be used on the special requirements of the proposed development or its location".

How To Use Vertical Sky Component Extension

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

  2. Open Vertical Sky Component dialog from toolbar VSC dialog icon or menu option Extensions-> De Luminae -> Vertical Sky Component -> Activate extension and enter the parameters of the calculation.

    DL-Light extension VSC Vertical Sky Component 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 VSC palette tab
  4. After all data are entered in VSC dialog, select one or few surfaces and press Render or run_selected button.

    DL-Light extension VSC 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 VSC Sketchup result imported - 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. To explore created images user can open folder where they are saved open_snapshot_folder_icon.
    This option is not supported in trial version of the extension (see licence information).

    DL-Light extension VSC Sketchup model snapshot image