This fern needs high light, your light spectrum may be incorrect for this plant. I would say place it near a window for better results. I believe you''re missing the red-ultra-violet range.
If this fern was recently purchased and taken from a place of natural sunlight to a place of artificial light, you will lose all of its leaves before new ones that are more adapated to the poor light conditions develop.

Flounia, it looks like you have the same fern I have, Microsorum diversifolium. I just got mine about two weeks ago at Lowe's. The information I've found leads me to believe it's pretty easy to grow and does well in moderate/low-light conditions, and also that it isn't a big fan of sudden change, but can recover easily.