Dear Gergely Fehér
Since the year 2000 I’m creating and updating the 3D libraries for various softwares like 3D Max, Autocad, and recently Revit, and those for the purely lighting industry such as Dialux, Relux and AGI32.
During the development in GDL of our product lines I noticed that there are some limitations in managing IES files, I can better explain:
In all softwares that allow to manage the IES photometry there is the possibility to display the photometric solid in wireframe mode so the final user, who has just inserted the lighting fixture, immediately sees the direction in which light is emitted.
Ok you can tell me there is the directional arrow of the light source that helps the intuition but in our opinion is not enough.
Below find the same lighting fixture with the display of the photometric solid (pic 1, image taken from DIALUX): you will also understand that you will not need to make the render to think where the light will be directed.
In Archicad once the lighting fixture in inserted on the floor, it is not possible to understand how the light will be directed (pic 2) if front, left, right or on the opposite side of the wall. The only solution is to make a render (in our case with a fixture the time to perform a render is very short, but if it is a large environment with several fixtures, the calculation time increases a lot) (pic 3).