This article was previously published under Q307442
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When you unplug your portable computer from an AC power source so your computer is only using battery power, the display may dim.
This behavior can occur when Windows XP dims the display to reduce power consumption and improve battery life. Note that this only occurs if your computer's basic input/output system (BIOS) supports the alteration of the display brightness level when you are using battery power, and your computer is in Advanced Configuration Power Interface (ACPI) mode.
This behavior is by design.
You cannot alter this behavior in Windows XP, but you may be able to alter this behavior in your computer's BIOS. To determine if you can alter this behavior in your computer's BIOS, view the documentation that is included with your computer. Note If you use Windows Vista, you can visit the following Microsoft Web page for help with power consumption and battery life problems: