I just recently learned that dandelions are supposed to be able to be grown indoors under normal lights and tried it. After several days under a roof with torch and fire lighting, they're still at .02% growth. It therefore no longer appears possible. Also, the in-game description states they need at least 51% light. I was hesitant to simply make the edit to this page since it looks like the text regarding their suitability for indoor growth was updated only a couple of months ago.