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I have a (minor) problem with switchable graphics on my laptop (Lenovo T520, NVidia Quadro NVS4200M and some Intel, drivers up-to-date).
When I run an action on Windows 7 that requires an UAC confirmation, my screen goes black before showing the prompt, just like when changing screen resolution or something. On my previous laptop (with a single graphic card) I haven't noticed anything like this, only the usual gray shadow. That's why I believe the issue is caused by switchable graphics.
This is not a very serious problem, it maybe takes a little bit longer to show the message box (on the other hand, I find it quite slow on every machine I use...), but it's annoying.
I know that Win7 is no Linux, so I don't really expect that there is any solution, but maybe... :)
EDIT: I've found Stop UAC/Secure Desktop from dimming the screen, which solves the issue, but at some cost. I just like the screen dimmed, I don't want it to go black before it get's dimmed.
Yes, I know that maybe it's a bit over-customization, but we're at superuser.com, right? :)
This is not necessarily related to switchable graphics; I've seen it on desktops. I've never really cared, investigated, or really thought about it, but I'd guess it's video driver specific. – Shinrai – 2012-06-13T17:35:08.797
1I've experienced this on old/slow PCs. I assume the graphics card can't render the transition smoothly (for whatever reason), so you get this flash to black instead. Setting UAC to "not dim" is the only workaround I've found. – iglvzx – 2012-06-13T18:26:08.080