Expected lifetime of the 20" Cinema Displays?

There are two versions of the aluminum 20" display. The early ones have brightness of 250 cd/m² and contrast of 400:1
<http://support.apple.com/kb/SP79>
Newer displays have 300 cd/m² and 700:1
<http://www.apple.com/displays/specs.html>

Also, if a display has been used for a long time at full brightness, the backlight will be a bit dimmer.

As with any LCD monitor or TV, the lifetime depends on the life of the backlight bulb. They are often measured in thousands of hours, but the lifetime is also often measured not in when it goes dark, but when it reaches a specified brightness level like 50% of original.

I have never seen Apple publish the lifetime hours of its backlights. It's useless to guess because you'll find TVs and monitors advertising anywhere from 3000 to 50000 hours and then you have to guess what the end-of-life brightness level is considered to be.

If you leave it on 8 hours a day then that's almost 2000-3000 hours a year depending on whether it's every day or just Mon-Fri. After a few years a drop in brightness will be noticeable but who knows how fast exactly. Like the other post, I have also heard that driving a monitor at full brightness will accelerate deterioration. Full brightness is too bright for color-critical work anyway, so if you are a photographer or designer who has calibrated to a proper brightness to match ink on paper, your monitor might last longer simply because it isn't practical to run it at full brightness.

Mine is exactly 4 years old and still looks brand new.
Has been used every day for 4+ hours per day.