I'm making a thing where there's no light source, so it's very hard for the player to avoid the falls and holes in the floor. So to make it easier, I want to make it so that every block within where the playing is standing, lights up.

Here's an example, since I explained that horribly.
There's a tunnel, that is 50 blocks long, and 10x10 blocks. When a player steps on any block, all the blocks in that 10x10x1 (WidthxHeightxLength) area light up, so the player can see where stuff is if they fail, so they won't die a million times.

So basically you step on a block, and all the blocks on a 1 block thick 10x10 area light up.

I would love for it to just spawn an invisible light source on every air block in that area, but I don't think you can do anything with light sources other than placing items and blocks that emit light. There's an empty 10x5 area all the way through the tunnel, so there might be a glowstone block spawned in the middle of that area.

I just don't know how to do it. I know it would be something with testfor, and setblock. But I'm not sure exactly how it would be done.