Brassavola seedling leaves got blackish lines along midrib

[sweta]

Hello Orchid pals,

Need some help in identifying leaf issue on a brassavola nodosa seedling that I ordered from olympic orchids 2 months ago. It was doing well until last couple of days leaves have developed dark lines along the midribs. Its potted sphag moss and medium pine bark chips. I water whenever medium dries out and I keep close watch on it since its a seedling. I've recently moved it away from window sill due to cold weather. Im and placed it under LED growing lights. Fertilize it every alternative week. House temperatures are around 70F and humidity about 30%. Could this some kind of fungal infection? Or could it be cause by the growing lights? Please suggest what could be the cause for this.