I'm not familiar with the Illumination Series specifically, but generally I think tuberous begonias need to cool off at night. Maybe even prefer lower humidity in the daytime. I grew tuberous begonias when I lived on the West Coast, where they have both those conditions, but never tried them when I lived in Nebraska (grew quite a few other begonias tho') and tried a few that were supposed to be more tolerant of heat and humidity here in south Louisiana, where I found they didn't like as much as we have anyway. But there are many, many others-----! Of course, it is sometimes an advantage to have them dormant in the winter!