You don't really need to understand the safety margins as such. Just make sure that your source sends out the image so that it maps the black and the white levels correctly.
If you value your system enough to spend £15 on a Blu-ray test disc for video
and audio then I can heartily recommend Digital Video Essentials HD Basics
link Despite the "Basics" name it has everything you need to do a thoroughly comprehensive job of setting up both the video and audio sides of any system. It's one of the test discs I carry and use a lot.
The pattern that you would find really useful is this...
The three dots at black and at white show the correct dynamic range for video. If you get the output setting wrong from the source then the test pattern will show it really clearly. It's a simple and very effective tool for this kind of setting.
If you've spent hundreds or even thousands of £££'s on your system, and countless hours researching and tweaking, but the idea of parting with £15 is just too much to bear then there's always
AVSHD It's a collection of test patterns put together by enthusiasts and offered as a free download that you burn to Blu-ray then play back from a BD player.
Another disc worth looking at is Spears & Munsil. There's a short thread discussing the merits of various discs and downloads
here