Lux Extension

Introduction

The Daylight illuminance (Lux) extension calculates the daylight illuminance on a SketchUp model using climate data.

Measuring the illuminance in natural light in Lux on surfaces is the basis for the calculation of numerous metrics such as Daylight Autonomy, sDA, European Norm EN17037, etc. It allows the user to use raw data on which he/she can apply various metrics.

This extension provides the average Lux on a surface according to 2 modes:

• Average calculated in relation to the hours of illumination. Use case: evaluate the average illumination during a day, without specifying the limits, but without taking into account the night hours.
• Average calculated over the entire period (including non-illuminated hours). Use case: compare illuminances over a specific interval, for example from 8am to 12pm over two seasons, taking into account the different sunrise times. 500 Lux during the 4 hours of the interval is then different from 500 Lux during 2 hours, i.e. an average of 250 Lux over the interval.

The extension also provides the maximum illumination values ​​of the sensors.

The calculation of Lux takes into account materials and inter-reflections. The number of bounces can be set in the preferences (10 by default).

How To Use Lux Extension

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

2. Open The Lux extension dialog from toolbar or menu option Extensions -> De Luminae -> Daylight illuminance (Lux) -> Activate extension and enter the parameters of the calculation.

   

   Fields description:

   • Project name - Project name is used during export and for output filename generation. The SketchUp model name is used by default.

   • Results - Directory where model will be exported for calculation.
     When calculation is started model geometry and resulting files will be saved in lux_output' subdirectory.
     For SketchUp projects stored on network disk (Windows), see Work on a copy of the model.

   • Analysis - Results represented by false color textures can have different meanings depending on selected value:

     • Average - Average illuminance over the period.
     • Maximum - Maximum illuminance for each sensor over the period.

     In trial version of the extension only 'Average' option is supported. For more details read License information.

   • Details - Models may require different density of sensors. Level of details definition is directly connected to number of sensors or their density on surfaces. Big unobstructed surfaces may need lower level of details with few sensors only, while smaller surfaces or surfaces with complex obstructions may require very high level of details. Level of details determines number of sensors for calculation, and has a major influence on calculation time and results accuracy.

     DL-Light allows to choose:

     • the sensor grid applicable by default to all calculated surfaces,
     • different sensor grids for some surfaces ("exceptions" button).
     

     See sensors selection for more information on the choices of proposed sensors.

   • Ground albedo - Reflection factor of the ground. Value can be selected from drop-down list or defined custom value in the following dialog.

     
     

   • Location - Building location coordinates. This info is used in combination with weather data to generate correct sky distribution. Location can be based on SketchUp model location, current Weather file location or be Custom. Below is dialog for Custom location definition.

     

   • Weather - Select annual weather file for the building location in Energy Plus weather file format. The weather file can be selected in the list provided by DL-Light or downloaded from Internet. See page Weather data.

   • Time zone - Display of the time zone used for the calculations.

     The time zone is defined by the selected climate data file.
     Nota: when a model is located in SketchUp, SketchUp proposes a time zone based on the longitude of the place. This value is sometimes wrong, especially for European or Asian countries.

   • Average / - Choice of period interpretation for calculating the average.

     • All hours - All hours are taken into account, including night hours.
     • Daylit hours - Only daylit hours are used for the calculation.

   • Period - The analysis period, defined by a season, the entire year, or two specific dates:

     • Season, year - select one season or complete year. The results will be summarized for selected period.

       Default seasons are defined for northern hemisphere. Advanced parameters allow to use different definition of seasons. Read details.

     • Custom - Define the period by starting and ending dates. 4 modes of definition of the period:

       • Full days - occupancy range from 0h00 to 23h59 on the day range (end date included). Click on the input box and choose the date in the calendar, or enter it directly.

         

       • Hours per day - occupancy range in hours on the range of days (end date included).

         

       • Start / end - interval between start date and end date.

         

       • Complex - use a complex definition of period. See complex period configuration.

         

     In trial version of the extension only 'summer' and 'winter' periods are supported. For more details read License information.

3. Define materials characheristics.

   Since calculation is done with verified Radiance tools it is necessary to 'attach' physically based material to each tag (layer) in SketchUp. Note that materials should be defined with their solar reflectance and transmittance.

   The tab for choice of materials:

   

   Materials panel consists of two main parts:

   • SketchUp tags table contains list of all tags defined in the SketchUp model. Each row contains SketchUp tag name and attached material name if any. If text in a row is gray, corresponding tag is not visible in the model. The table is updated in real time, as SketchUp model is modified.
   • Materials tree contains all material libraries available for DL-Light extension. Some of them are provided when extension is installed and others can be imported or created by user. Subtree 'Model materials' contains materials currently attached to SketchUp tags.
     To explore available libraries and add new ones, see Materials libraries dialog.

   To attach a material, select in the table tag(s) and either double-click on required material in the tree or select the material in the tree and press Attach/Detach button.
   To detach from the tag(s), select it and click Attach/Detach button.
   To revert all tags to previous state press Revert button.

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

   
   • The automatic palette is generated during calculation and is based on calculated results for selected surfaces. This is the best option for first calculations, when user doesn't have idea about possible resulting values
   • Gradient palette enables global palette manipulations - definition of minimal and maximal palette values, number of colors and start and end color. It is very useful once user have idea of resulting values, but want to experiment with colors.
   • Custom palette gives full freedom to add/delete/modify each color separately. Good for creation of final results for representation, when some surface areas should be highlighted for example.

5. After all data are entered in Lux dialog, select surfaces and press Render or button.

   

   Calculation time depends on number of selected surfaces, level of sensors details and model's complexity.

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

   

7. Results analysis.

   • The Report dialog displays the distribution of results over current palette, and calculation input parameters.

     

   • Show/Hide Sensors and Values explores results directly in the model for each sensor.

     • Note : SketchUp's "View / Guides" option must be enabled.
     

8. For further calculations on the same model:

   • To run calculation on any surface simply select it and Render .
   • It is possible to modify the parameters of the calculation: to change the density of sensors to improve the visualization of the results (for all the model or a specific surface), to modify the palette of colors, to change the time period... Whatever the change, use the Render button. Previously calculated surfaces will be updated with the new settings.

   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).

   For example if a calculation has just been made for the "summer" season, then the season is changed to "winter" for a recalculation, and finally recalculated for "summer":

   • the system will redo the calculation of all the surfaces for the "winter" season, avoiding some steps: calculating the location of the sensors, preparing the weather file.
   • When the "summer" season is requested again, all the data can be restored from the cache, the "calculation" does not take more than a few seconds.

9. 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.

   • To archive the calculation results, click on the button Archive.
   • To load the results of a previous calculation, click on the button Load

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

10. Snapshots:

    Current SketchUp model view with imported results can be exported with palette or without palette to png format. To explore created images user can open folder where they are saved .
    This option is not supported in trial version of the extension (see license information).