Hardware buttons (hot keys)
Many portable computers include hardware buttons or hot keys for changing the display brightness. Typically, users access these hot keys by pressing a function (Fn) button in combination with another key on the keyboard.
In Windows 8, each time the brightness up (or down) hot keys is pressed, the display brightness will increase (or decrease) by 10%, regardless of the number of supported brightness levels. For further details on hot keys and how the Windows display brightness is translated to an actual display brightness level, see Integration with hardware buttons (hot keys) and How actual display brightness is determined.
Hot key-based brightness changes invoke a brightness overlay on the upper left corner of the display. The overlay provides feedback to the user by showing the new brightness level. Similar to the Settings charm, users can tap or click on the overlay and drag up or down to easily specify a relative brightness. Figure 1 Overlay displayed upon hot key brightness changes shows the brightness overlay.
Figure 1 Overlay displayed upon hot key brightness changes