LIGHTING DESIGN - Internal Lighting Calculations

Setting up the Analysis Grid

In this tutorial you will work through the process of analysing lighting levels, then design an appropriate artificial lighting grid to compensate for low light levels.

  1. Open  from the Tutorial Files directory located in your main ECOTECT Install directory.

    There only two zones in this model, one called Classroom and the default Outside zone.

  2. Before calculating lighting levels it is necessary to setup the Analysis Grid.

    Go to the Analysis Grid control panel, and click the Analysis Grid Settings button.

    The above dialog box is displayed. Enter values similar to the ones above, making sure the X and Y Grid Cells are the same (20 and 12), then click the OK button.

    Notice that the Z Offset for the grid in the Grid Position section of the Analysis Grid panel is set to 600mm.

    This is an accepted standard working plane height for lighting calculations. You can of course move the gid up or down to suit your needs. This is necessary if the floor plane is not at ground level, Z=0. Adjusting the height within a space will affect the calculated light levels.
  3. To display the analysis grid, select the floor object then click the Fit Over Selection button.

    This button stretches the grid to just under the extents of the object. It also hides any grid points that are not within the extents of the object.

    Before moving on and calculating light levels, it is important to make sure that the analysis grid is set appropriately. If the grid is altered in any way after calculations have been performed, the values will be lost.

    Also it is important that the boundary of the grid does not sit exactly on the surface of geometry. If this does happen, ECOTECT will find it difficult to determine if a point on the grid is on one or the other side of the wall. The result will look quite strange in that it will look light the walls are emitting very bright light (ie. from the sky).

Calculating Light Levels

  1. To calculate light levels, select the Lighting Levels option in the Calculate section at the bottom of the control panel.

    Then click the Perform Calculation... button to display the following dialog.

    Enter values similar to the ones above. You may want to set the precision to Medium to hasten the calculation process (though it will be slightly less accurate), then click the OK button.

    The above settings are a worst cast scenario for latitude -31.9. Worst case being defined by an overcast sky in the middle to winter. This corresponds to a sky illuminance of around 8500Lux. If your site is in a different location, either enter the design sky value directly if you know it or use the Calculate Design Sky options.
  2. ECOTECT starts calculating values. This may take a while - perhaps a good time to make a cup of tea...

    Once the calculations are complete, try altering the display settings. The above grid is displayed with Shade Grid Squares and Show Contour Lines on.

    Also try adjusting the Minimum and Maximum scale values as well as the Contours value to adjust the contour increment. To apply these settings hit the Enter key. You should also try experimenting with the other display options, such as the Show Values in 3D option.

Designing the Lighting System

Once the extent of natural lighting is established, it is possible to design an artificial lighting system to compliment the daylighting and light the space at night.

  1. The first thing to look at before moving on, is the natural lighting system. Using a minimum design requirement of 300 lux, it is possible to separate the two skylights, as around 700 lux is being achieved in the middle of the room.

    Hide the analysis grid temporarily (Unclick the Display Analysis Grid button in the Analysis Grid panel) and select one of the skylights. With Point snaps on, move the object 500mm away from the centre of the room (the easiest way is to snap to opposing end corners).

    Now do the same to the other skylight.
  2. Once this is done you may like to recalculate the lighting levels to see the effect.

    Separating the skylights slightly provides a much more consistent range of levels in the centre of the room, and reduces the area along the edge requiring additional artificial lighting.

    It is obvious that additional light is required along the junction between the pitched and flat roofs. As well, it will be necessary to provide a strip of lighting along the central roof line for operation at night.

    The two perimeter rows of lights could work from a single switch, however the central row should be switched separately as it will not usually be required during the day.

    The corners of the room are also a bit dark, however if these areas were to be used (which is unlikely) then task lighting would be more appropriate here.

Adding Electric Lights

  1. To add lights to the model simply click the Create Light button, then click a point in the model.

    In this case this is best done in in Plan view. Whilst you can drag the direction vector of the light, we want it to point directly downwards. To do this, hit the Escape get after you have positioned the first point.

  2. Once a light has been inserted it is necessary to move it up in the Z direction, as the default creation height is Z = 0.

    In side view (F6 or F7) make sure the light is selected, then hit the Z key on the keyboard to move the light in the Z direction by increments of the nudge value (default = 100).

    Move the light up until it is level with the flat section of roof (Z = 2400).
  3. Once one light has been inserted correctly, mirror it about the centre of the room.

    Make sure Apply to Copy is checked and the origin is in the right position.

  4. Now that we have the start of the two perimeter rows of lights, we need to add the first light for the central row.

    This can be quickly done by copying one of the existing lights and nudging it into position in the Y and Z axis. A height of about 3400 in the Z axis will be sufficient.

  5. Now that we have the first three lights we can array them in the X direction, with a gap of around 2000mm, to form the three rows of lights.

    The easiest way to do this is to use the Object Transformation panel (Modify > Transform > Numeric or Ctrl+T).

    Make sure the three lights are selected, then enter values similar to the ones shown to the left in the Linear Array group.

  6. Once entered, click the Create Array button.

    The final array should produce three rows of eight lights each, at 2m centres.

    At this stage the model may become cluttered with lines from the cones of the lights.
    To turn these off, in the Display menu go to the Element Detail pull-right and choose None.

Assigning Light Types

The next step is to specify the right properties for the lights.

  1. First make sure all the lights are selected, then choose the Material Assignments panel and click the FluoroLampStripUnit light material. Then click the Apply changes button at the bottom of the panel.

  2. Now recalculate the lighting levels in the space.

    Once calculated, you should be able to display only the effects of the electric lights only by selecting the Electric Light Levels option in the Grid Settings group.

    This should display levels similar to the following.

    You will note that total light levels (daylighting + electric lighting) are well above 300Lux, however the electric lighting alone does not reach this level throughout the room. Thus we need to either add more lights or use brighter luminaires.

    At this stage you may wish to experiment with some of the other types of light in the library or adding additional lights to attain an even distribution of 300 Lux across the room.

    Similar to other types of object in ECOTECT, the properties for lights are defined by the material assigned to the light. A future tutorial in this section will look at manipulating the light output distribution or lights and loading in IES data obtained from manufacturers.