How do I manually turn on the light

Alex Deucher alexdeucher at
Wed Feb 13 15:33:45 PST 2013

On Mon, Feb 11, 2013 at 12:49 PM, James Cobban
<webmaster at> wrote:
> On 13-02-11 08:32 AM, Alex Deucher wrote:
> On Sat, Feb 9, 2013 at 4:03 PM, James Cobban <webmaster at>
> wrote:
> I am running Ubuntu 12.10 on a Dell laptop with VGA compatible controller:
> Advanced Micro Devices [AMD] nee ATI BeaverCreek [Mobility Radeon HD 6620G].
> The Xorg driver works well except that when I close and reopen the laptop
> and the system resumes the light is not turned on to illuminate the LCS
> display.  Can I manually turn the light on?  If so how?  I don't see any
> activity on related bugs since 2010.
> I have had to switch back to the proprietary fglrx driver despite its
> problems because being able to close and reopen my laptop is higher priority
> than the improved display characteristics of the Xorg driver.
> What kernel are you using?  Does manually adjusting the backlight
> controls after resume fix the issue?  Are you using the acpi backlight
> interface or the radeon specific backlight interface?  Open a bug
> ( and attach your xorg log and dmesg
> output.
> Alex
> Ubuntu 12.10 with kernel 3.5.0-23-generic.  I am just running with whatever
> configuration the Ubuntu "Additional Drivers" graphical tool activates.  I
> do not know what that is.  I have no idea how to manually adjust the
> backlight controls, but the light is completely off, so I think that would
> be pointless.  I tried using "radeontool light on" to turn the light on,
> because I could see that command being issued by the script, but that
> did nothing.  I am not familiar with the capabilities of the acpi interface.

radeontool won't do any good for your chip.

> I just want to turn the light on!  I would not be asking if I knew what to
> do.  I do not believe there is an intrinsic problem that needs a bug fix.

In most cases the driver is able to resume fine and bring back the
backlight.  In your case it doesn't seem to be working.  You might try
a newer kernel.  I fixed some backlight issues in either 3.6 or 3.7

> The actual resume seems to be working fine.  For example I can telnet into
> the resumed system.  I think this is just a configuration error in Ubuntu
> for this particular hardware.  For example I get exactly the same behavior
> if I switch to the fglrx driver, using the "Additional Drivers" script, and
> then forget to run the "aticonfig --initial" script.  So I am confident that
> all I have to do is find the right command to turn the light on.
> I do not know what I am doing, so just tell me what to try.

As I said, normally, it should just work.  You can try adjusting the
backlight manually with sysfs.

To check the max brightness:
cat /sys/class/backlight/[driver]/max_brightness

To set a brightness level:
echo [brightness] | sudo tee - /sys/class/backlight/[driver]/brightness

replace [brightness] with whatever level you want to set and replace
[driver] with the name of the backlight device on your system.  You
may have more than one so try all of them.  E.g.,
/sys/class/backlight/radeon/, etc.


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