Toumnia folding several leaves

[Canadienne]

I have had this tolumnia for a couple of years, and it has grown well. Currently there are several leaves (on the photo on the right a larger leaf, on the bottom right another larger leave that is folding / closing.
It grows at 22C daytime, 19 C night, 50 % humidity, under lights 12 hrs a day in the winter months. Lights are full spectrum grow lights 6400K. It dries out between Waterings quickly. Medium a mix of lecca,pieces of fir bark, pumice. It is not broken down.It summers outside and does all of its growing then, young fans mature in winter without issue.
So why are the leaves folding? They don’t seem to be dying?

[Ray]

Hard to diagnose from afar, but consider these and see how they might apply:

• Natural senescence of old growths?
• Not enough light? (I would expect a bit more of a reddish tone.)
• Not watering often enough?

[Canadienne]

Thanks Ray, I have the tolumnias about 4-5” under the lights. It is my first winter grow8ng under lights. Should the distance be less?
Thank you for all your thoughts, they’re very much appreciated!