Also, you can find out what panel you have by opening the
terminal program in OSX and pasting the following command:
ioreg -lw0 | grep IODisplayEDID | sed "/[^<]*</s///" | xxd -p -r | strings -6
This method spits out the manufacturer code of the panel - different from Apple's mmod codes. You can then google the code to find out who makes it and view the vendor's spec. page. The credit for this info goes to MacRumors member JayLenochiniMac. It was posted here in a thread on 20" iMac panel quality. Here's the link for anyone interested:
https://forums.macrumors.com/threads/674462/