After a lot of strugglaing, using ColorEye Pro I have been able to get my iMac monitor luminance down to the 120 target, but I see that the Maximum dE = 1.49. Average dE = .55
I seem to remember (can't find the source now) that the dE should be around 1.0. Does this mean that my profile is still not acceptable? That is, that my prints will not match my monitor?
A couple of comments: First, an average dE of .55 is not bad at all. Second, the maximum dE of 1.49 is not so bad, either, especially if it occurred in the first few levels above black, which is natural for the kind of display you have. But the main question I have is how did you determine that 120 cd/m2 should be your target intensity? It is probably the suggested target, but it is dependent on your room illumination as well as the illumination used when you assess your prints.
My display is now calibrated and profiled at a target of 135 cd/m2. I tried luminance settings at the recommended 120, down to as low as 95, and back up to 140 and found that the intensity of 135 gives me the best results in my lighting.
The ideal situation is to set up a print-viewing situation where the brightness of the light on the print is the same as that coming from your display. At that point, your prints should not be darker or lighter than the softproof on the screen.