Noticed the other day that my echeveria in the front room was starting to get leggy. I'd suspected that spot didn't have enough light for them, but gave it a try. No good. Moved them to the other side of the house, where it's plenty crowded now.
The hornwort in the tank told me about light levels, too. In just a few days it went from looking rather compact to having more internodal spacing. So I know the person who kept them before me had higher light levels in their tank.