© 2012 Above the Fold

UI DESIGN 20
Obey real-world rules
Even if you don’t favor faux-real interfaces like Apple’s iBooks, almost every
interface you design will take some cues from real-world physical effects like
lighting and perspective. Make sure those effects are applied consistently and
sensibly; otherwise it’s easy for users to become disoriented.
For example, if your buttons have a highlight along the top edge, and a
gradient that darkens at the bottom, that implies a light source shining from
above. Don’t switch it up and include other elements on the same screen that
look like they’re lit from below.
Apple’s iBooks app uses realistic lighting to depict a bookshelf.
Tip
Looking for more details? Check out the chapter on visual principles in
Stephen P. Anderson’s book, Seductive Interaction Design.