My T410 (i5-520M, intel graphics, WGXA+ screen, 65W battery) and I've noticed that when I'm on battery power, the brightness of the screen is unstable. I'm not talking about the brightness kicking down several notches when it sits idle. It wavers or flickers slightly, kind of like watching the 40hz refresh flicker on a CRT. Sometimes the brightness fades in or out by up to a full notch relative to the normal brightness control, like it's being underpowered. It happens at any battery level, but does not happen when I'm plugged in.
This symptoms may be resolved a number of ways - the recommendation is to update to video driver version 126.96.36.1993 or later from the support site.
CHANGES IN THIS RELEASE Version 188.8.131.523
[Problem fixes] - Fixed an issue where the screen's contrast ratio might randomly change when powered by the battery.