Ambient light sensor configuration?

[Paul Shaffer]

Is it remotely possible the Infinity 24hr.-by-hr. animation wallpapers are the source of your consternation here:
   
  http://fedoraproject.org/wiki/Artwork/F8Themes/Infinity/Round3Final#head-0afce1582af5a054f81558f0e4148b3b6a445bbd
  

Sam Varshavchik <mrsam at courier-mta.com> wrote:
  Rick Stevens writes:

> On Thu, 2007-12-13 at 19:41 -0500, Sam Varshavchik wrote:
>> Frank Cox writes:
>> 
>> > On Wed, 12 Dec 2007 19:57:55 -0500
>> > Sam Varshavchik wrote:
>> > 
>> >> My laptop seemingly has an ambient light sensor, of some kind, and the 
>> >> kernel apparently knows about it, but won't let me access it. 
>> > 
>> > Are you sure it's kernel-controlled? Perhaps it's 100% hardware.
>> > 
>> > Try covering that sensor when you're looking at Grub and see if it brightens
>> > or dims the screen then.
>> 
>> Tried that. No response in Grub, the LCD backlight begins reacting to the 
>> ambient light sensor as soon as the kernel boots, even before initscripts 
>> mount all the filesystems.
> 
> Can you disable it in the BIOS?

There are no BIOS settings, and it only begins working after the Linux 
kernel gets loaded. As I said: the sensor is not active when Grub's menu is 
shown, only after the kernel is loaded.

This is but a minor irritation, but I want to track it down just for the 
sheer mystery factor: here I have this hardware device that all evidence 
suggests is directly supported by the kernel. It does not get activated 
until the kernel boots, so it cannot be purely a BIOS-controlled function. 
It is not control by X.org, or Gnome, because I can get the light sensor to 
react even before initscripts mount their partition. Direct support in the 
kernel is the only choice left.

Yet, I find no apparent kernel module, and I find nothing in /proc or /sys 
that gives any hint of this sensor's existence. The only thing I can think 
of is that this is an ACPI function, but my knowledge of ACPI is rather 
scant.

This is an irritant because my normal light levels in the room happen to 
just hit that sweet spot where the ambient light sensor starts dimming the 
LCD backlight just slightly. The dim function is not absolute, it is 
gradual. The sensor can dim the backlight in small steps, between full and 
less-than-half regular brightness level.

So, with the ambient room light level right at the top of the sensor's 
threshold, for the longest time I thought that my eyes were playing tricks 
on me, because I could've sworn that the brightness of the laptop's display 
kept flickering back and forth.

Only some time later did I discover of the sensor's existence (because 
nothing in Gnome, or /var/log/message gave any hint of its presence), and 
figured out that the stupid thing was frobbing the LCD backlight's power a 
few notches back and forth, with the ambient light level right at the top of 
the sensor's threshold. It was driving me nuts, until I figured this out. 
Now, I just want to turn the blasted thing off, and leave the LCD backlight 
at full power, all the time.

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