Could it be that the fan means they are drying out between watering? Having the light on longer would make that worse. Maybe not much more water, but more frequent doses, but a bit smaller ones. try to keep the dampness of the soil constant. That would be consistent with them going brown. Otherwise I am running out of ideas and hoping someone who knows more about growing with lights comes along.
TBH this General chat form is probably not the best place to get noticed for this problem. If you click on 'Forums' at top left and go down the list you will see there is a forum 'Indoor Plants' just after 'Roses'. If what I am saying is not a help and no-one else replies it might be worth re-posting there.