Distance between Lights and Tower

Hi everyone,

So I also want to setup a hydroponics system at home to have fresh grown salad, herbs and maybe other stuff in winter. I bought the tower and lights as attached and now want to build some kind of "housing" around the tower to also hold the lamps in place.

The main thing I am concerned now is the distance between the light and the tower/plants. If I build the hounsing it will be difficult to adjust the distance later so I would like to know if someone could tell me what would be suitable? I have have 4 of these LED panels so I was thinking of putting one in every corner.

If more information is required please let me know, and thanks already for the help!