When waking Macbook Air 2012 from the Login Screen, the display flashes, then works normally. Mildly concerned.

Getting the same problem. Have reset the PRAM too, as thought that might work, but had no effect. Have just tried turning off mirroring to see if that works.

Had same issue here, after enabling power nap con battery mode, screen flashes 2 times when opening the lid.

Disabled it and now works ok. A very annoying bug.

Run

OnyX for Mac

http://www.macupdate.com/app/mac/11582/onyx

http://helpdesk.hsc.unt.edu/wp-content/uploads/2010/02/Mac-OS-X-10.6-run-OnyX.pd f

I have tried everything, and am still have the issue with the screen flashing brightly twice after waking the Air from sleep. It seems to be a hardware issue with Mountain Lion. Anyone fix this issue? I have tried all suggestions within this post.

not just macbook air afflicted with this. my 13" retina macbook pro has it, too. it's some sort of bug introduced in 10.8.2.

along with that, mountain lion takes far too long to enable the login prompt from sleep - upwards of 30sec in some cases. too many times, i've ended up with just the end of my password entered and the shivered you got it wrong response from the o/s. this happens on my imac, my macbook pro, and happened on my retired macbook air. the corollary to that is when putting the imac to sleep, it can take over 30sec for it to be effective. this is new in 10.8.2. 10.8.0 was slow to wake. the latest updates have made its behaviour worse.

well tested, apple!

I had the same problem with my mid 2009 MacBook Air after the latest Moutain Lion 10.8.2 upgrade but it seems to have been solved for me by:

(a) Enabling the Power Nap (it was off) in Enery Saver -> Battery

(b) Unchecking the "Show mirroring options in the menu bar" in Display

("Automatically adjust brigthness" is turned on on my MBA)

(c) Locking the Enegy Saver preferences

I have tested various combinations of sleep/restart/log-out with lid closed and then opening it and I don't get the flicker any more.

It could be a long-term rather than short-term problem as others have commented so will continue to monitor (sorry - bad pun!)

(a) Enabling the Power Nap (it was off) in Enery Saver -> Battery

(b) Unchecking the "Show mirroring options in the menu bar" in Display

("Automatically adjust brigthness" is turned on on my MBA)

(c) Locking the Enegy Saver preferences

didn't help... The problem is still there (((( MCA 13" mid 2011

Apparently it's flashes only on battery power... if you plug in power before opening the lid, it's logs in normally...

the other thing I notice, it flashes if network changes... i worked in the morning at home, closed the lid, open at work and it flashes... and same thing in the evening... Apple support didn't help, and had no idea what it could be... to me it is obvious bug in Mountain lion... hope Cupertino gyus are monitoring this...

That's exactly what I have. Thought it was something to do with me trying to partition my drive to run Ubuntu & OS X, so deleted the Ubuntu partition - but still it flashes. Very odd.

Same flash issue when waking up 13" MBA (2012) after sleep on battery. Showed up after 10.8.2 update. Very annoying. Before I noticed the flash, it would lock out the mouse/keyboard input for a few seconds so I couldn't type in my password. Now, the last few days, it does that, then flashes white before becoming usable. This is a brand new machine with a fresh, clean install of Mountain Lion. Very frustrating, but I'm glad to see it's probably not hardware based, due to the other comments in this thread.

My flashing went away, but I've still got a delayed log-in screen; it shows up but doesn't let me enter anything for a good five seconds, plus the screen is dimmed.

Davidnave's suggestion seems to be the best one so far. Since deleting the file, my MBA has stopped flashing (which had gotten much worse in the past week before trying the fix. I am not experiencing the delayed lon-in sceen either.