After returning a new 24 inch iMac two times and getting the replacements I figured out that the problem is not related to the particular machine, but rather to all of them. I read tons of forums and the issue is so widespread that it leaves no doubt it’s a design fault. A design fault that Apple is leading us to believe they are not aware of, despite hundreds and thousands of calls to their customer support asking for help.
The problem is essentially this, the display is brighter on the left than it is on the right. Much brighter. Below is an illustration of how the brightness is distributed across the screen.

There are three areas of interest here:
1 – The display gets darker closer to the left edge of the screen
2 – The display brightness is constant
3 – The display gets darker towards the right side of the screen
Apple tries to compensate for this with ridiculously high level of brightness, which to be honest masks the problem rather well. The screen is simply so bright by default that any normal human being either needs to have sunglasses while using the iMac or turn the screen brightness down. The problem is, you can turn the brightness down only so far. And that is very little. Even the lowest setting is still way way too bright for most of us.
Here is the drill – the lower the brightness, the lower the panel temperature. The lower the temperature, the darker the edges of screen, hence the gradient. I am sure Apple is aware of this and this is exactly the reason why they keep the thing so bright.
I tested a few free utilities that will let you darken the screen further, and the one that best suits my needs is (or are) Shades. Shades actually doesn’t darken the screen by reducing the brightness, but rather applies a transparent overlay of specific colour. The default colour is black but you can change it to any other colour in the preferences window (not that I could imagine someone using a pink overlay).
The slider, that you can have either in the menu bar or on the desktop, doesn’t really change the brightness but the transparency of the overlay, which in turn makes your screen to appear darker.
What I did was to reduce iMac brightness to the minimum, then apply Shades to darken it a bit further. This made my display reasonably dark, but also produced even heavier gradient.
My wife, having heard me talking loudly to myself about the panel temperature and being frustrated with the gradient, came up with a brilliant idea… and not so brilliant solution. She laughed and said “If you need the temperature, why don’t you put the blow heater next to the screen, on the right end”.
This actually made me thinking and, of course ,brought up the answer to the problem. Turn up the iMac’s brightness control all the way up to generate enough temperature, then darken up the display with the Shades overlay.
The display brightness is now flat across the screen. When I wake up the computer in the morning there is a little of gradient along the right edge, about 2 inches, but within a few minutes this is gone.
One thing that may work against this is the screen calibration. I have noticed that some custom calibrations I have made have resulted in an unusual pink-ish tint towards the right edge, but Adobe RGB and sRGB work perfectly fine.














