Screen dims after 40 seconds inactivity

[gizmo4321]

I'm trying to figure this out, and not having any luck.

Under System | Preferences | Power Management

The Power Management Preferences dialog has a tab for 'On AC Power' and 'On Battery Power'.

Each of those tabs has a checkbox marked 'Dim Display when Idle'.

If I check that checkbox, the display dims after exactly 40 seconds of inactivity. It doesn't care what I have the screen saver's "Regard the Computer as Idle when Inactive For" slider set to, it doesn't care what I have the Power Manager's "Put Display to Sleep when Inactive For" slider set to.

Can anyone shed some light on where this 40-second time-out is coming from and how I can control it?

[tashirosgt]

Fedora Core 11? What is the Power Manager's "Put computer to sleep when inactive for:" set to? Is your computer a desktop or laptop?

[gizmo4321]

F12, but I had the problem with F11, too.

Computer is a Lenovo Thinkpad T61p laptop, and I'm running F12 64-bit.

Power Manager's 'Put Computer to Sleep when Inactive for' is set to 'Never' on both AC and Battery.
'When Laptop Lid is Closed:" is set to "Susped" on both AC and Battery.
"When battery power is critically low:" is set to "Hibernate" on Battery.

[tashirosgt]

The only thought that comes to my mind is that the BIOS of the laptop itself might have some way of dimming the screen. Can you boot the machine from something like SystemRescueCd and leave it in the text mode? See if the screen dims even without Fedora.

[gizmo4321]

That would be a valid suggestion, except that if I un-check 'Dim display when Idle", then the display brightness doesn't change. If it were a BIOS setting, then would it not work the same either way?

Also, I didn't have this problem with F10 (I gather that F11 reworked the backlight-control logic?).