A more realistic atmosphere

This is a couple closely related ideas on diffusion.

I'd like to see light diffuse a bit.  It's not realistic that a small overhang 50 blocks above you makes the block underneath it dark.  I'm not sure exactly what ratio it should be, maybe for every 10 blocks the light goes in the down direction it diffused out 1 block?

You could also simulate wind by having rain do the same thing (possibly with a variable ratio to simulate different wind speeds.)  This would kind of have to include having the clouds change direction to the direction of the prevailing winds.

The light level changes would affect spawning.  The rain being able to be blown in under ledges could allow some farm land to be irrigated, and maybe leaving a programming hook in there would make for some interesting ideas for modders (mods that affect players being wet, or mobs that only spawn in the rain).