What happens when you calibrate a screen?

Well, in rough terms:

The software asks your target settings for gamma, white point and luminance in nits (candela per square metre), depending on the software package you will be asked to adjust the luminance using the brightness controls on your computer at some point while it displays the actual value.

The software then displays colour patches and compares the values issued to the value measured by the Colorimeter (the puck) - it will adjust the graphics cards LUT to correct the values where needed and if possible. Any corrections and deviations are recorded in the ICC profile (a text file with values). If you now assign this profile to the display (System Preferences - Displays - Color), OS X will automatically load the assigned profile data into the LUT on start-up and colour-managed applications saving images will embed information on what you have really been seeing into each file, so other devices can render a truthful reproduction (within their capabilities).

Hope this helps a little...

Gamma: http://www.normankoren.com/makingfineprints1A.html#Gammabox

A light definition would be the amount of contrast in midtones - the gamma value does not effect pure black or white. For photography and video work you will normally use a gamma of 2.2.

The white point should be D65 (6500 Kelvin) or "native"

Target luminance for print proofing should be between 90 and 120 cd/m2 depending on the ambient light - 90 for a rather dim environment, 120 for normal office lighting - you should not use LCDs in completely dark environments for proofing and, of course there should be no direct light.

LUT = Lookup Table, http://en.wikipedia.org/wiki/CLUT

The brightness issue is more delicate with LCDs, as there are two factors involved: the backlight (controlled using the brightness controls) and the voltage applied to the individual sub-pixels (red, green and blue) making up each pixel. The backlight cannot be dimmed any further than the lowest setting of the brightness control - the calibration has no effect on that, it is more or less just a lamp with a dimmer. What the calibration can adjust to some degree, is the luminance level of the individual subpixels. The difficult part here is tweaking the output per pixel without giving up desirable contrast, desirable white and black points and maintaining a smooth rendition of grayscale gradients... there are quite some calculations going on there. As a result - yes, a good calibration software can lower the brightness of a LCD (below the backlight only result) within some limitations. I cannot comment on the Spyder 3 (it is brand new and I have not used it) - I can definitely say that Color Eyes was the only software that could really tame the white 24" iMac (which had similar brightness) - Spyder 2, eyeOne and Huey all failed completely (calibration OK, but still far to bright for print proofing). You could overcome the issue with software tools like Shade, but I cannot comment on the quality of this approach, as I have not tried it.

If you do not need non-standard target settings (unlikely, unless you deal with e.g. offset printers), I would really try to get a Spyder 2 Express. It is a lot cheaper (where still available) and comes with the same hardware as the Spyder 2 Pro. Getting a Spyder 2 Express plus the Color Eyes software will be more or less the same price as getting the new Spyder 3 Elite and taking the risk of not getting the desired results. Alternatively wait for reliable reports from Spyder 3 users with the 24" iMac - should not take too long before hearing from those. I would not really want to end up buying two pro packages... too expensive.

Not sure if there is really a problem - at 120 cd/m2 the screen should look a lot darker than before and your eyes need at least 30 - 60 minutes to get used to a greatly changed profile. Do not make the mistake of calibrating every five minutes if you think something is odd. It might be odd, but it might also be correct. Allow your eyes and brain to adjust to the new profile, then review test images (e.g. the ones that come with the Color Eyes download).

The correct settings for Color Eyes and the 24" iMac should be:
- Calibration Sensor (select the Spyder2)
- Monitor Settings (LCD Brightness Only) DO NOT USE Apple Display - it is for Cinema Displays only!
- Profile Settings (ICC v4, 16bit, Auto-validate)
- White Point Target (D65, 120 cd/m2)
- Gamma Target (L*)
- Black Point Target (Min. Lumincance)

Make sure the monitor is on for at least 60 minutes before calibrating and make sure to use some really black material for calibrating the sensor (e.g. use the cloth that came with the iMac).

Printing is a completely different issue: which software did you use, which printer/paper profile, what was the Color Management setting in the print dialogue? Always make sure colour management in the printer driver is off - for most printers using "No Color Management" and the correct paper profile will work best, but for some consumer printers the "ColorSync" settings works better...

HTH

Message was edited by: Uwe Rueckeshaeuser1, reason: typo

Well, my copy of Color Eyes (the latest AFAIK) always tells me to put the colorimeter on a black surface at the beginning of a calibration (before putting it on the screen). If yours does not, try checking "always calibrate" in the "calibration sensor" settings.

If you are not getting asked to show the puck something black, check the settings for absolute vs relative calibration.