**If you build your spawner on the surface (rather than in the sky), you will need to find and light up all of the caves, there is no way around it.**

Personally I find the "x-ray machine" to be "cheating" and instead have my own technique for finding caves. Create a grid of holes about 8 or 16 blocks apart (depending on how accurate you want to be). These holes should be dug from the surface to the bottom of the map (or at least until you reach the infamous "lava layer"). The added bonus with this technique is these holes to the surface will also prevent any void fog at the bottom of your world.

![MineCraft holes to surface][1]

If you use this technique, to be on the safe side, put everything except the necessities (torches for if you find caves, and tools needed to dig: pickaxe, shovel, sword; all of which can be of stone or iron) in a chest so as to not loose it if you fall into a pool of lava or appear in a dangerous area.

  [1]: https://i.sstatic.net/4yDGp.png