Dell Premier KB900 User Manual page 23

The backlight is turned on as described in the table below:
NOTE: If the ambient brightness detected in your environment is bright enough,
then the backlight will not turn on to conserve battery life.
NOTE: While charging, the proximity sensor is disabled and the backlight is always
turned on. The brightness of the backlight depends on the user setting or if no key
is pressed within 30 seconds then the backlight will fade to the lowest brightness
setting which is 25%. When you turn off the keyboard then the backlight will also
turn off.
Action
Hand is detected (within detection range of 2-4cm)
Hand is detected (within detection range of 2-4cm), but
no key is pressed for 30 seconds
(Hands are resting on the keyboard).
Hand is no longer detected
Wireless keyboard is charging
Wireless keyboard is charging but no key is pressed
within 30 seconds
Backlight status: On
On
Fade off after 30 seconds
Fade off after 5 seconds
On
On but after 30 seconds fade to
the lowest brightness setting
Intelligent backlighting │ 23