Sounds like the backlight behind the LCD is going out.
Reset the SMC and then test: http://support.apple.com/kb/HT3964
Reset the PRAM and then test: http://docs.info.apple.com/article.html?path=Mac/10.6/en/26871.html
If the issue persists after you follow the above steps you are experiencing a hardware issue and your system requires evaluation and / or service. You may wish to make an appointment with a Mac Genius at an Apple store, contact AppleCare via phone, or contact an Apple Authorized Service Provider for assistance.
Resetting SMC and PRAM... I do it reguarlly - is not helping.
These resets should only be done to troubleshoot an issue. They are not maintenance techniques. Careful of overuse.
If you have AppleCare on your system, contacting service as I suggested above would be advisable. If you don't have AppleCare you could still contact a local Apple Authorized Service Provider to get a price estimate if you are interested.
Best of luck to you.
Briefing for the iLost in CyberSpace with same problems... seems there's a problem with late 2009 iMac 27" models (?). I'll turn in the iMac for a service check (Apple Store). So far Apple has been very kind and helpful without giving a specific answer - what part of the iMac is the problem? Is it the screen? The backlight? A tiny little connector... ?
I've found several people with same problem. Just talked to a good friend this weekend... mentioned the problem. We bought the iMac's at the same time. I bought mine for home, he bought two for his work. And he has exactely the same problem with one of the two iMac 27" he bought!
Is the late 2009 iMac 27" a monday model ?
It is the first shipment of the 27" iMac's!
what part of the iMac is the problem? Is it the screen? The backlight? A tiny little connector... ?
Most likely the backlight but when you take it in for service they will diagnose the issue. I have the same model as you and have no such issue so I would not go so far as to say its all the the 27" iMacs. Taking it in for service is the way to go.
I'm sure not all are faulty... As mentioned my friend bought two for work, one has same problem. Let's hope number of faulty iMacs from early 2009 doesn't increase! It's first line of the 27" iMacs.
Probably it's the backlight but user report similar case
mention that exchanging the backlight doesn't help the iMac backlight problem - left side of screen.
But I'll turn it it to an AppleStore to have them look at it. Already talked to Apple and mailed with the store.
Still - would like to know what causes the problem! But I'll be back.
A little status. I didn't turn in my Mac as expected. Could not do without it at the time... we're talking about the home altar! But I expect it will be a bill of aprox. 7000-9000 danish kroner, that's 1200-1500$ - or to have it diagnosed aprox 150$
Soooo... instead I bought a second monitor and a connector. Samsung by the way That's only aprox 230-250$. And I don't have to turn in my home altar...
Good thing though - the dark spot is not getting worse over the past half year.
I have talked to Apple about the problem - but they couldn't or wouldn't tell me what the problem was. I'm sure they know... it's not an uncommon problem with late 2009 iMac's.
This is happening to me on a 27" Imac bought in 2011. Left side of the screen is flickering and periodically going quite dark. Apparently I'm 40 days out of waranty. From doing a couple basic google searches I find this is a common issue with these LG manufactured screens in the 27" imac's from 2009 to 2012. But Apple isn't issuing a recall... Cant wait to see how much a repair will cost - I hear $1000 for apple to do this. Cant believe a 1 year old computer that costs over $2k is failing already - and the problem is this widespread.
Take a look at this report: https://discussions.apple.com/thread/4041042?start=0&tstart=0
I've had my 2009 iMac opened - when I added a ssd harddisk - but didn't dare messing with the soldering. But the problem could be a simple as that. I'll live with the black spot/area - till it's time getting a new iMac.
thanks hansenodsense. guess Ill take the thing apart and get the soldering iron out. i bought the computer to do some photo editing so I really cant live with apples shoddy construction/poor engineering causing the left side to be this dark. if I mess something up I wont be buying another imac because it seems this issue is happening still with 2012 computers! Get your act together apple.