Growing deciduous tree's under grow lights will create other issues for the plants themselves , the humidity will cause fungal diseases if the humidity is too high and lacking good air circulation . You can fight mother nature all you like but in doing so you will different problems .
I have Chinese Elms here some are dormant others are in Autumn colours while others are sprouting new leaves . Mother nature herself is confused . All of my elms are from the same seed batch and in the same grow beds
This basically looks like a leaf that has done its job and wants to die , your addition of grow lights and humidity has possible added to the spotted colour and possibly a minor fungus issue . Leaves and needles on tree's only work for so long as mother nature planned .
Just my
worth . Cheers Alpineart
