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When I disconnect my laptop from AC power, its screen becomes more dim, in order to save battery. When I connect it back to AC power, it becomes bright, because now it's not concerned with battery level.

I appreciate this logic, but I prefer my laptop stay at the same brightness level regardless of whether it's plugged-in or not. How can I accomplish this?

(I'm using Windows XP.)

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up vote 4 down vote accepted

Look at your power management settings (try Control Panel | Power) or your laptop may have a manufacturer-supplied program to handle this. Usually these let you create and/or select power management profiles, which can include screen brightness settings.

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I've looked there before asking this question, nothing there. – Ram Rachum Nov 9 '11 at 16:56
    
In that case, perhaps check with the laptop manufacturer, or mention here what make and model it is; perhaps someone will know how to change the setting. – Steve Rindsberg Nov 12 '11 at 3:59
    
It's a Samsung Series 9. The manufacturer's support line told me to look for a power manager program myself, but I don't know any good one that does this, and I hope someone here knows. – Ram Rachum Nov 12 '11 at 12:38
    
I'm adding a new answer ... take a look there. – Steve Rindsberg Nov 13 '11 at 16:55

My XP laptop is a Lenovo; they do supply a power manager that has quite few more options than XP's control panel. I had a look in the registry to see what's there and found this:

HKEY_CURRENT_USER\Control Panel\PowerCfg\PowerPolicies\11

(the finall number will vary depending on which policy you've chosen, apparently)

Interesting entries (all REG_SZ strings, not DWORDS)

DISP_BRTNESS_AC=7
DISP_BRTNESS_DC=1

BRTNESS_WHEN_IDLE_AC=7
BRTNESS_WHEN_IDLE_DC=1

BRTNESS_IDLE_TIMER_AC=0
BRTNESS_IDLE_TIMER_DC=0

You might be able to add these entries to your existing profile to get what you're after.

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I tried playing with all of these, but nothing happened. – Ram Rachum Nov 14 '11 at 12:27
    
That leaves me w/ no more suggestions, I'm afraid. – Steve Rindsberg Nov 15 '11 at 16:36

Some laptops have a screen dimming option in the BIOS. If this option is set to dim on battery, then no amount of fiddling in the OS will turn it off.

I had a Lenovo X61 that did exactly this. No idea about the Samsung Series 9. That's a "Designed for Windows 7" laptop, anyway. While XP may be supported, it might not be supported well.

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I searched the BIOS now and found nothing related to screen brightness in there. – Ram Rachum Nov 16 '11 at 17:07

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