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When the power cord is removed from a laptop, the display brightness goes down slightly (very slightly, not a complete "notch").

The interesting thing is, I don't remember XP doing this, it seems to be new with Windows 7.

Already checked the power plan, and set both battery and plugged-in brightness to 100%, so it shouldn't be Windows. Could it just be that the battery can't sustain max brightness on it's own? Or is Windows 7 not fully following the power plan?

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I have seen this on many laptops, I don't think it related to Windows 7 specifically. –  soandos Dec 18 '11 at 5:13
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Do you have any vendor power management installed, or only W7? –  Paul Dec 18 '11 at 7:20
    
@Paul - Only Win7, I installed from the retail disc, no OEM cruft :) –  Unsigned Dec 18 '11 at 14:56

2 Answers 2

Control Panel\Hardware and Sound\Power Options (or type power options in the start search box)

This should show you your power plan. Then select "Change plan settings" to find out when the display dims when on mains or battery power.

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Already checked the power plan, and set both battery and plugged-in brightness to 100%, so it shouldn't be Windows. Could it just be that the battery can't sustain max brightness on it's own? Or is Windows 7 not fully following the power plan? –  Unsigned Dec 18 '11 at 14:57
up vote 0 down vote accepted

Seems that the battery cannot maintain the voltage level. Manually measured the monitor power leads and noticed a drop there.

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