/dev/keylight:

This driver controls the key backlight.  It is controlled by apmd, which issues
ioctl()'s to the driver:

KEYLIGHT_MAIN_ON
KEYLIGHT_MAIN_OFF
KEYLIGHT_MAIN_SETTING

KEYLIGHT_AUX_ON
KEYLIGHT_AUX_OFF
KEYLIGHT_AUX_SETTING

MAIN seems to be the keylight in the flip

AUX the keylight of the poweroff and home buttoms at the bottom of the device