Which screen do I need for a Lenovo t530?

You have to open the lid and get the model number off of the back of display itself.
The reason is that the LCD panels and LCD inverters are paired - one inverter probably won't work with a different screen. Get the model off the back of the screen and search for that.

Samsung screen

"CTO" is a designator for Configure to Order".
Unless you try to research your LED Drivers and commonality of parts or changes in a sub-card, the safest path is like-kind replacement and only choice is matte or glossy or other external coatings or glass.

Thinkpad T series used to have a CCFL (Fluorescent backlit) inverter card that was changed to an LED Driver Sub-card, and I don't have the specifics any more as I'm out of that business for a few years now, retired, and with no specific records. I can't swear one way or the other if the same LED Driver card is used on x1080 vs x768
http://www.laptopscreen.com/
I believe is the leader in replacement screens, though certainly there are other sellers.
T530 2359CTO leads to here:
http://www.laptopscreen.com/English/model/IBM-Lenovo/THINKPAD~T530~2359-CTO/
and agreed shows only x768 and x900
And, the 2359 machine type shows only those two offered.

If you do not know your resolution, and suspect it is not the standard x768, your two choices is just buy the x900 that should be right, or re-verify by pulling out your LCD screen that you will have to do anyway, and find any markings for part numbers to google its specifications.

Lenovo, following IBM tradition, is very good about making a service guide available.
http://download.lenovo.com/...474_02.pdf

The LCD is not considered customer replaceable, meaning they don't give specifics.
But, knowing Lenovo (I was a respected Procurement Engineer there for Thinkpad)
http://support.lenovo.com/...s/pd024402
Yields:
04W0430 N CMI 15.6"HD
04W154 N AUO 15.6FHD
04W3260 N SEC 15.6"HD
04W339 N LGD 15.6"HD AG
04W341 N AUO 15.6"HD AG
04W345 N BOE 15.6"HD AG
04W346 N Samsung 15.6"HD+ AG
04W3471 N AUO 15.6"FHD AG
42T0743 N LGD 15.6 HD+
42T0763 N AUO 15.6 HD+

HD = x768, HD+ = x900, and look, 04W3471 as an AUO brand FHD (x1080)

Another knowledge of the inside says there's a different production use part number, and an image search indicates part number 0A66674,
A label like this:

You may indeed have an x1080. It would be smart to use this paper information and try to verify what is in your laptop by a label on the LCD per IBM >> Lenovo procedures and should say 0A66674
If it has a different number, it is not at all likely to be a x1080.

AU Optronics B156HW01 v.4
http://www.panelook.com/B156HW01%20V4_AUO_15.6_LCM_parameter_686.html

That is about as close as I could get without physically seeing your LCD backing with its label.

You will have to do the rest yourself. The AO brand panel, Lenovo product part number of it, FRU (Field Replacement Unit) part number all should be consistent and can be googled and searched for a seller of your choice.
YOU can confirm the panel yourself now that you have all this information available.