The Layout Assistant is an easy avenue to quickly estimate average illuminance levels and make adjustments to luminaire quantities as needed to meet your criteria.  To start, simply enter the quantity of luminaires you plan to use.  Layout Assistant will immediately display an average illuminance estimate for the quantity entered, as well estimates for plus or minus 1 luminaire. 

The estimation algorithm used to produce the estimate is significantly more powerful and accurate than the Zonal Cavity based methodology built into Revit.  Layout assistant employs the same radiosity engine used by the calculate commands , and estimates results quickly by applying a very coarse mesh to the environment.

There are many options in the Layout Assistant dialog to tinker with the luminaire positions.  When you’re happy with your layout, place the luminaires in the Revit model by clicking “ok”. If you want more confidence in the illuminance estimate first, perform a full calculation using the “Calculate” button.