Rosanna Foxfire

So, I've never noticed this before, but today someone in my FC brought up that casters often close their eyes while casting larger spells. And Arcanists close or shield their eyes for every spell, having tested it out some. So I got curious, is there a lore reason for this? Is it just shielding our eyes against the bright lights of the gathering aether? Another theory was that it's our characters concentrating on gathering the necessary aether to cast the spell. So what're y'all's thoughts and ideas for this? Is there a reason?