Compaq 1610 Reference Manual page 31

The dual brightness backlight button provides you with two levels
of backlighting (the light that illuminates the screen). The
following table describes how to use the backlight button
according to the handheld PC model you have.
Press
backlight button
Press Fn +
backlight button
Using the backlight drains battery power. To conserve battery
power, use the backlight on the lowest setting that is
comfortable for you, and use it only when necessary.
To save battery life, you can set the device to automatically
turn off backlighting when using battery or external power.
Tap Start Settings Control Panel double-tap Display
Properties. Select the Backlight tab and choose the settings
you want.
To automatically turn on the backlight whenever a key is
pressed or the screen is touched, select Advanced from the
Backlight tab and choose the settings you want. (Applies to
monochrome models only.)
Toggles backlight
on
and off.
Toggles between
normal and high
backlight and sets
the selected level
as the default.
Toggles between
normal and high
backlight.