ahh not surprised its that low. its about 4yrs old. And likely explains why my 2011MBP looks a lot better.(MBP is also LED backlight. I have just not desired to upgrade this one since its a good sized screen and still works just fine.)
however... Even for a non-Apple computer it would seem that using this fun link. »members.ping.de/~sven/dpi.html
providing its accurate. for high resolution displays in the 27" range the Apple Cinema has the best dpi at 108.