First, we will read current brightness values set from the desktop framework.
Asleep, screensaver image or ad showing:
[root@kindle /]# cat /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
FrontLight(Intensity) = 0
Awake, slider at maximum brightness:
[root@kindle /]# cat /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
FrontLight(Intensity) = 254
Slider adjusted to minimum brightness (almost off):
[root@kindle /]# cat /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
FrontLight(Intensity) = 1
Slider adjusted to medium brightness:
[root@kindle /]# cat /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
FrontLight(Intensity) = 36
Now we will see if we can CHANGE the screen brightness from the command line:
Lets try to SET maximum brightness:
[root@kindle /]# echo -n 254 > /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
Yes, it works!
Now let's try to turn it COMPLETELY off:
[root@kindle /]# echo -n 0 > /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
Yes, it is completely off even while awake!
Now, lets put the Paperwhite asleep by tapping the power button. The light is off. Now set maximum brightness:
[root@kindle /]# echo -n 254 > /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
Yes, it is showing the screensaver image at maximum brightness.
Now let's turn the screensaver light off again to save battery:
[root@kindle /]# echo -n 0 > /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity
It is off again.
Now, I think that is useful!
EDIT: Now that we know how to change screen brightness from the command line, it is time to write a script to blink out Morse Code messages...