The highest contrast ratio of the Lenovo T2254 is 3000000:1. That's 40% less contrast ratio than a 5000000:1 LCD screen, which is the most common contrast ratio. The best contrast ratio of all PC displays that have been available for around the same time as the T2254 is 100000000:1 and the worst is Mega Contrast.
It may also be worth considering one of the other PC screens that have a 3000000:1 dynamic contrast ratio currently available including because of it's better review score, the HP ProDisplay P221 (£129.99).
If the contrast ratio of this Lenovo LCD screen is not high enough for you then you might want to look at the LG 22MP47 (£139.57) (5000000:1), the HP ProDisplay P222 (£312.23) (5000000:1), or the Medion Akoya P54421 (£99.00) (5000000:1).