What do the small-sunrise / big-sunrise icons mean on F5 and F6 on the MacBook Air? What do the F5 and F6 keys do on the 2011 MacBook Air?  They are marked with what I interpret to be small-sunrise and big-sunrise icons.  I do not see any effect when I press them.
These are for decreasing and increasing the brightness of the keyboard backlight. When the system senses low light and the keyboard is allowed to illuminate, the keys will work. Otherwise, they silently do nothing at all.