If I am not mistaken the component to define electrical light sources based on IES files is not yet added to LBT-Radiacne. I wonder if there is any plan to implement it soon, or you can suggest any workaround to integrate the Radiance text file without the component?
If your goal is light planning with radiance i would suggest to have a look at Relux Desktop relux.com
This free frontend app is running radiance in the backgroup and comes with a huge ies luminaire library ready to plugin.