Chosen Solution
Hi! I just bought a brand new (unused still sealed) imac 27” 2017 off eBay, and once I power it on, and the black boot screen appears I can see that some areas of the screen is brighter/lighter than others, but once I use the screen, like in final cut or word etc, it isn’t clear - is this a serious flaw or? ive run diagnostics on the Mac, and it all comes back clean with no faults, and I’ve checked the display quality & built in terminal (using “system_profiler SPDisplaysDataType” command) and it’s all ok. ive attached photos to show how inconsistent the black level is when the machine turns on.
I’m suspecting you are seeing the basic limitations of LCD panels Black Uniformity Of Monitors The gap between the two panes of glass supports the liquid crystal material. The thickness of the liquid defines the degree of polarization of the light the thicker the material the darker the black but there is a limit of going to far! As the helix of the liquid can cause the image to lose its crispness as it gets thicker. This then gets into how parallel the plates are from each other so the liquid is thinner or thicker at different areas. The size of the panel is what makes this harder as the plates are only supported along the edges. You can see this effect just by touching the panel the area around your finger will get a bit darker as you push the liquid out from directly under your finger is now thinner. Newer displays use zone backlighting to reduce this effect (review TV’s to see more about this) even still thats not changing the liquid or the glass only masking it. And if that display was here, in the boot up this same image would likely be seen. I wouldn’t put too much worry on this as you also could be just seeing the brightness is set at the extreme. Adjust it down will lower the effect.
