It's a little different, the F91W has a little light that shines from one side onto the front of the LCD display whereas (if it's anything like my Casio W86-1) I think the F105W is backlit. So they both have a light, but one is much clearer.

edit, just confirmed that this is the case:

F91W light: https://i0.wp.com/thetruthaboutwatches.com/wp-content/upload...

F105W light: https://media.karousell.com/media/photos/products/2021/7/19/...