a writes:
After inadvertently hitting some random keyboard letter key the screen went considerably dim. I then went to bios adjusted brigtness individually for both battery and non battery operation. The brightness holds up part way into computer loading at startup,then dims.Is there a non bios control of which I am unaware.I welcome an analysis.
Unfortunately it varies by manufacturer, but have a look into /sys/class/backlight. On both of my current (Intel graphics) machines, the file is /sys/class/backlight/intel_backlight/brightness so you can do things like cat /sys/class/backlight/intel_backlight/brightness or echo 3000 > /sys/class/backlight/intel_backlight/brightness (from a root shell). On my Asus the maximum is 4800 but I suspect that varies with make and model. Debian used to give me automagic controls on Fn-F6 and F7, but that stopped working when I upgraded to 64-bit stretch so I had to set up my own key bindings that used the /sys/class method. And yes, there is something during the boot sequence that restores the brightness from some saved value, but I don't know where that code lives. I have the impression that it's restoring from whatever /sys/class/backlight/intel_backlight/brightness was when the machine last shut down, so if you use that method to set the brightness to what you want, hopefully that will fix your problem. ...Akkana