Thanks for the question. Usually you setup the target of lux level based on the application|space that is defined in standards and as well in Dialux. The surface calculation is giving you an exact value for a specific area defined by you, compared with the overall lux level as you can see in this video from minute 15"52. Hope that everything is clear now.
Thanks for making such a useful tutorial, I want to ask if I can analysis with this software dalylighting of an atrium/Skylight building with actual daylight ( natual light) instead of artificial lighting.
You are welcome! Yes, you are able to run a daylight calculation if you insert a skylight into a room and you plan to check the amount of natural light in that room. Watch the video related to daylight calculation: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-O6xZ2PGIfSs.html