Marc, that is exactly what an IES files does. You use one of these files and it automatically gives an accurate representation of the output. They actually do 2 things, they define the light strength in real world units, and the shape of the light distribution.
Because these things are defined as data, you don't need to have a realistic model of the actual geometry. If you do have a reasonable model of the geometry and can specify light strength in watts, you don't need IES files.
The benefits are accurate calculation without needing the geometry of the fitting. The drawback is that not every fitting you want to use has an IES file. If you want to use specific fittings that don't have the data available, you have a problem.
LightUp's proposed features should allow you to use IES files when you want, and when they don't exist, you can model the fitting and still get a good representation of the output. I don't think it will give you the calculation in lux levels though - unless Adam is planning to add that.
Adam - sorry, I didn't mean to imply that IES would be part of LightUp. These sort of things aren't for me to announce 😳
I just thought this was potentially an excellent use for your application. You don't have an example of this sort of thing in your gallery which is a shame because it's a great idea. It doesn't seem logical to me to export a sketchup model to a lighting program to get an inferior visualisation if you don't want a numerical analysis of the light spread. You should be able to get a much nicer realtime drive-through within SketchUp using LightUp.
