Lights in Archicad have several categories, so it would help if you picked just one light source to ask about.
I suspect that if you are having trouble, it is more the falloff setting rather than the light intensity that will be the issue. More falloff = less overall intensity.
Light settings can be complex until you arrive at a solution - that can be re-used. Users get more success lighting scenes as a photographer would rather than by trying to make each architectural lamp do the work.
Dwight Atkinson
