Re: Ambient light sensor configuration?

[Paul Shaffer <ace_wizard@xxxxxxxxx>]

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@xxxxxxxxxxxxxxx> 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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