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The correct monitor luminance for you will be based on the level of ambient light in your editing room. It's the ratio between the ambient and the screen that determines the correct perception of screen brightness, if you will. Unfortunately, there are no hard and fast rules for these numbers, but it's not hard to figure out with a little trial and error.
More important in your monitor calibration is, of course, the monitor luminance as measure in candelas per meter squared (cd/m2), which on an old fashioned CRT would have been around 85 cd/m2, but with most LCD screens will be in the 120 cd/m2 range. For the same perception you need to raise the ambient room levels to compensate.
You should never, however, change the brightness of you screen after you calibrate. To do so completely invalidates your monitor profile - which is describing the total calibration parameters to Ps - and will never give you an accurate view. Set you monitor luminance in your calibration software and leave it there.