Yellow tinge from bottom to top of the screen, 27" iMac

Just waiting to send back my second one week 10, for a refund. I'm going to wait until this issue is straightened out.

Okay Stefan. Try the following. I did so on my machine first. 1) Click the Apple symbol in the upper left hand corner, 2) Click on About the Mac, 3) Click on More Information, 4) Visually scroll down to serial number on right side, highlight and copy, 5) Enter serial number into the following website which should provide you with information about the production week (excuse the German): http://www.chipmunk.nl/klantenservice/applemodel.html. I am curious about whether you have an old machine from stock or one of the newer production models. Thanks.

Ever since returning my 21.5 imac I've been doing a lot of research on other IPS panels by visiting forums, blogs, etc.

My conclusion: This is a common problem to ALL LG manufactured ips displays. For example, check out the following pic of a U2410 screen - look familiar?

http://en.community.dell.com/cfs-filesystemfile.ashx/_key/CommunityServer.Components.ImageFileViewer/CommunityServer.Discussions.Comp onents.Files.3529/3858.DSC_5F00_0650-small.jpg_2D00550x0.jpg

Some have worse issues with a pink to green fade that goes diagonally across the screen - now that I think of it, I thought my 21.5 was a bit greenish on the right compared to the left, but I was so focused on the yellow tinge I didn't really give it much thought.

Other issues are the "IPS glow" which seems to account for the vast majority of complaints regarding backlight bleeding on these screens.

Basically, we need to accept that this isn't exactly a thoroughly tested technology, so chances of getting a screen with problems is much higher than otherwise. Those among us who are picky about these things should probably wait a year or so before picking up an IPS screen (or until Dell and Apple use a company other than LG to manufacture their screens)

Also, here's a handy list of 24" IPS screens that are made by LG (not sure how accurate it is):

NEC LCD2490WUXi-BK ....... LG.Philips H-IPS A-TW Pol (LM240WU2)
Hazro HZ24W ................... LG.Philips H-IPS (LM240WU2)
Philips 240PW9EB .............. LG.Display H-IPS (LM240WU4)
Apple Alu 24" .................... LG.Display H-IPS (LM240WU2-(SL)(B1))
HP LP2475W ..................... LG.Display H-IPS (LM240WU4-SLA1)
Eizo CG243W .................... LG.Display H-IPS (LM240WU4-SLA1)
Eizo SX2462W ................... LG.Display H-IPS (LM240WU4-SLA1)
Dell U2410 ........................ LG.Display H-IPS (LM240WU4-SLB1)
HP DreamColor LP2480zx .... LG.Display H-IPS A-TW (LM240WU5)
LG W2420R ...................... LG.Display H-IPS (LM240WU5)

I just got notice that they are overnighting my second iMac from Union City, CA (???). This is odd, as my original came from Shanghai, China. It should be here tomorrow.

I am getting my replacment i7 from Shanghai. My replacement order was started March 16 and the order status says "ships 2-4 days" and "not yet shipped."

None are built in the USA no matter what the code says. They may be finished here but from what I have heard, assembled in the USA is hooey. My first two imacs (i5s) were "assembled in the USA." Third (i7) was from Shanghai and the replacement CTO also Shanghai.

kos213 wrote:
Basically, we need to accept that this isn't exactly a thoroughly tested technology, so chances of getting a screen with problems is much higher than otherwise. Those among us who are picky about these things should probably wait a year or so before picking up an IPS screen (or until Dell and Apple use a company other than LG to manufacture their screens)

My first reaction seeing this photo is : where was the QC (if any) on this? 😟

I would not say "this isn't exactly a thoroughly tested technology" but rather something like "difficult to test when the manufacturing process constraints are high".
Remember the first panels (week 39-42 2009) where not that bad! But when production rate increased....

As I already mentioned earlier here, there are no white LEDs. Instead (on panel of this grade) blue LEDs coated with a yellow emitting phosphor are used. The two wavelengths appearing white to the human eye, when mixed. Same thing with the fluorescent lamps (CCFL) using also phosphor coating.

Panels using this LEDs technology are particularly difficult to build with color uniformity due to operating temperature gradient on the array of LEDs (variation in temperature can be responsible for shifts in the emission spectrum). This is the thermal management issue pointed by Apple in its Patent. This is IMHO the current state of the art *in this grade of displays* ... (the problem name is 'backlighting' not LG, Samsung or whatever).

This is my conclusion too.

But another added issue is that the emission equilibrium of the LEDs has a relatively long stabilization phase, making the measurement in the production environment a challenge.

"The final production step for LEDs is the optical characterization and the subsequent sorting into so-called BINS"

This sentence maybe gives a decisive clue : very hard to test in the manufacturing process.
This is why IMO very good panels are so expensive.

The phrase is extracted from a very good article, by Dr. Thomas Nägele, –in the LED professional magazine I received late 2008- regarding white LEDs and measurement standards.

http://files.me.com/jacques.laporte/cbj4c4

Take a look, it is probably a good part of the story.
Cheers.

That's a really interesting article!

So what I gather is if the manufacturer could somehow allow enough time for the LEDs to stabilize (i.e., complete its burn-in phase) and then take measurements, discarding and replacing those that are emitting a color temperature that is totally off, we would have more uniform screens. This would, of course, take forever and be completely impractical in a large-scale production setting.

However, my question is, is the yellow (green, pink, whatever) tinge not related to IPS screens? Or have other LED backlit screens been afflicted by the same problem?

kos213 wrote:
That's a really interesting article!

However, my question is, is the yellow (green, pink, whatever) tinge not related to IPS screens? Or have other LED backlit screens been afflicted by the same problem?

IPS tech is relatively old (end of '90s) and has to do with the improvement of the viewing angle of TN LCD panels. The common defect associated with TFT was, at that time, a slow response time (in all the technical literature I have read) but not color shift, as far as I know.

It's really difficult to diagnose such a device only from the outside. That's why I will stop here my investigations and enjoy my iMac.

But one thing I know (I posted earlier articles on that point), the color shift I see on my screen is *from blue (top) to yellow pinkish (bottom-right)*. If I push the white point up to 6750 Kelvin, the screen looks globally less warm and there is no more pinkish bottom corner.
But it's more icy blue, on top. No free lunch.

I have changed the blue-yellow balance but the gradient remains.

It signs IMO a white LEDs thermal problem.

Note : High grade tricolor LED (RGB) backlit panels do exist and are not plagued by this issue. They use special hardware to monitor variability in brightness and color and ensure a low Delta-E difference across the screen. The price is also high grade 🙂

Name: iMac Intel (mid 2009)
Group1: iMac
Group2: Intel
Generation: 7
ModelCode: imac mid09
CPU speed: 3.06GHz
Screen size: 27 inch
Model introduced: 2009
Production year: 2010
Production week: 07 (February)

Jacques,
Thank You for the very interesting article.
It certainly sheds some "scientific" light on this whole long discussion.

I also feel it is time for me to start enjoying my new iMac.

Good Computing
DavidH

Thanks Stefan D for the information. Your machine was built in February; it is only a month old. This is really your call. I have a 30" ACD which I thought was "perfect" until I did the gray bar test. Knowing that there are flaws I am still comfortable because it does not affect my daily use of the Mac. I would use the following criteria for possible exchange: 1) It negatively affects something you are doing or likely to do with the Mac (photo processing, graphics, etc. or 2) It is prominent in daily use and will likely continue to bother you. If neither of these conditions apply, returning an otherwise machine in good condition does run the risk of incurring additional problems. It has happened to other posters and some of these issues were not avoided by opening the box in the store and taking a quick look. It is up to you.

DHood wrote:
Jacques,
Thank You for the very interesting article.
It certainly sheds some "scientific" light on this whole long discussion.

I also feel it is time for me to start enjoying my new iMac.

Good Computing
DavidH

You're welcome David, Have fun too.
Jacques.

Called apple support just now. he spoke with the senior advisor and he said I can try one more time and they will test it before I leave to make sure I don't leave with another tinted one.

Message was edited by: Stefan D