Regardless if its needed always, or just for certain activities like reading a lot of people and ponies need glasses. Then of course there are those that wear glasses as more of a fashion statement. It could be always or just during certain events or times like say a nightmare night costume.
No matter what glasses aren’t uncommon so for lunas challenge draw someone or somepony with glasses. Are they using them for something specific? getting new or their first pair? In the end you have 30 minutes to pick some glasses and who they belong to. As long as there are glasses it counts.
After that the inbox will be open 15 minutes. See you then. get it? see you? i’ll just go to the corner now for my bad joke.