I use a Spyder 4 pro system to calibrate my monitor and while colour balance has matched prints from good online photo printers I frequently have problems with the density not being as expected from looking at the monitor image ,so clearly the monitor calibration has produced too bright a screen. Some people online suggest setting a brightness of 120 cd/m2, but my monitor is not sophisticated enough to quantify brightness levels in such units. Therefore I came up with this objective method which others who have the same problem may find useful, it worked for me. I placed an 18% Kodak grey card on a bookshelf in the same lighting environment where I hang prints, set the camera on spot metering and with the lens de-focused made an exposure of the card using the meters recommended settings. I was careful to not allow any shadows to fall on the card as this was done in daylight and the card was facing a large window. I then turned the card around and made an exposure of the white side keeping the same settings. Next I loaded the grey card image into Lightroom cropped the central portion of the card and pressed F so it filled the monitor screen. Standing back at a good viewing distance I took a spot meter reading from the centre of the image and adjusted the monitor brightness until the camera meter indicated an exposure which was the same as that used to make the actual image . Then to check I was on the right track I loaded the white image on the monitor to see if the camera meter indicated the same exposure as that used to make the grey card image, which it did, I have to say that the white card looked a bit greyish but I trusted the objective power of the metering and went with what it was telling me, which was that the monitor was now emitting the same amount of light which the card had been reflecting when placed on the downstairs bookshelf. I just got some prints back from the online photo printer and the subjective result is that what looks right on the monitor screen in a darkened room also looks right in the print in bright daylight. And about bloody time too.