The Calculate Lighting Load command is used to display the total load in kVA on a selected group of light fixtures.
To determine the lighting load for select light fixtures, go to
Ribbon: DM Electrical->Devices-> 
Calculate Lighting Load
Pulldown Menu: DM Electrical->Light Fixtures->Calculate Lighting Load
You will be prompted to select light fixtures.
Select objects:
A Design Master Electrical dialog box with the lighting load displayed will appear, as shown below.
Press the OK button to close the dialog box.