To enhance or reduce light output to reflect environmental factors in the project, change the Light Loss Factor value for the lighting fixture. 
 This change affects all relevant project views. 
- In a project view, select a lighting fixture, and click Modify | Lighting Fixtures tab
Properties panel
 (Type Properties).  
- Click Duplicate to create a new type. 
 
- Enter a name for the type, and click OK. 
 
- In the Type Properties dialog, for Light Loss Factor, click in the Value column. 
 
- In the Light Loss Factor dialog, specify the desired value.