The light loss factor is a value used to calculate the amount of light lost due to environmental factors, such as dust and ambient temperature. 
You can define the light loss factor for a lighting fixture family file (as follows). In a project, you can change the light loss factor of an individual lighting fixture. (See Changing the Light Loss Factor for a Light Source.) 
To define the light loss factor
- Open the lighting fixture family. 
 
- Click Create tab
Properties panel
 (Family Types).  
- For Name, select the family type to modify. 
 
- Scroll down the list to locate the Light Loss Factor parameter, and click in its Value column. 
The Light Loss Factor dialog displays. 
  
- Specify the calculation method for Light Loss Factor: 
Simple calculation
- Specify as follows: 
- For Method, select Simple. 
 
- For Total Light Loss Factor, move the slider to adjust the value between Dimmer and Brighter. 
 
- Click OK. 
 
  
 Advanced calculation
- Specify as follows: 
- For Method, select Advanced. 
 
- Under Value, adjust the sliders for each parameter, or enter a value in the text box. 
See Light Loss Factor Parameters. 
  
- Click OK. 
 
  
 The Family Types dialog displays the new Light Loss Factor value. 
  
- Click OK. 
 
- Save changes to the lighting fixture family.