I looked around for something like this, but all I found were a lot of other posts asking if there was something like it. So, here is the request:
A block that prevents mobs from spawning within a certain range.
At it's most basic, it would be something simple like mobs don't spawn in a 16x16 block cube around the block. Better would be a set of blocks with different ranges and possibly shapes, 8x8, 16x16, 32x32, cube, sphere, etc. And better still would one block you can interact with to select a range, somewhat like chicken chunk loaders. The recipe doesn't need to be expensive, after all it just replaces a few torches and is, for the most part, an aesthetic alteration.
As is, it is extremely hard to have an "atmospheric" build unless you use half slabs everywhere. Yuck. Preventing spawn without tying it to light levels would be a boon for countless people and hopefully get rid of the truly horrible "torches, torches everywhere!" syndrome minecraft suffers from. So much so, I hope it is one day a vanilla feature.