I am running Ubuntu 16.04 LTS on an HP 2560p laptop (64-bit). After finally getting the ALS to work, I have a strange problem with setting brightness using the keyboard keys, with ALS (ambient light sensor) enabled.
On my machine,
cat /sys/class/backlight/intel_backlight/max_brightness returns a value of 648. Using the keyboard keys fn + f10 I can increase the brightness, to a maximum value of 616 and still have the display on. If I try to go to the maximum brightness, using the fn + f10 key, my screen goes black. If I run
cat /sys/class/backlight/intel_backlight/brightness when the screen is black, it returns the max value of 648.
I can live with this, but it would be nice to have this working correctly. I have intel_backlight which is being used by including "
acpi_backlight=vendor" in grub.
I tried to
echo 616 > /sys/class/backlight/intel_backlight/max_brightness, to lower the set max brightness to a value I can use, but no dice (can't edit that file and also tried to have it done during boot using rc.local which also didn't work).
If it helps at all, on the low brightness end, I use fn +f9 to decrease bightness. On the lowest achievable level,
cat /sys/class/backlight/intel_backlight/brightness returns a value of 8. The indicator bar of the brightness applet, on the lowest brightness setting, still shows a bit, indicating (?) a further decrease in brightness may be possible(?).
Can anyone help with this? I admit I am quite the noob, but when googling for this problem I didn't find a thing. Basically, it seems that the max_brightness value of 648 (set by hardware demands?) is an incorrect value (if that is even possible).
One idea I have as a workaround (although I've no idea how to achieve it) would be to limit the applet function somehow, to reduce its maximum value to 95% of max_brightness (616/648 = 0.95) such that when I use fn + f10 to increase brightness, I will not be able to set it higher than 616 (or 95%).
Any comments or help would be appreciated.