How can you hide light sources while they still give light?
Light will shine through paintings, but paintings have to be placed over solid blocks (which signs count as!), so you could make a wall like so:
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The hole in the middle would actually be 2 deep; you'd place a torch in the back, then a sign in front, then put a painting over the hole/sign; the torch would shine through the sign and painting, and light up the room (although the light would be somewhat diminished because the torch is recessed by 2 blocks).
WITH TORCHES
STEP 1:
STEP 2:
STEP 3:
WITH GLOWSTONE
BEFORE:
AFTER:
One of the newest features, carpet, makes it extremely EASY to add lighting to your house without the need for fancy tricks.
Carpet allows light to show through, so easily placing Jack O Lanterns or Glowstone underneath carpets in your home allows for easier lighting, without all the hassle.
You could try these two methods of my own:
Raise the floor with stone slabs, and put glowstone around the bottom. Note: In newer versions of Minecraft, this no longer works. Since 1.4.2, half slabs block light from passing through them. So although you can see the lit glowstone (and smooth lighthing may cause the surrounding area to light up a bit), there isn't any "real" lighting going on, so the rest of the room will still remain dark, allowing for things such as mob spawning.
Hide glowstone in a location you can't see it, and let the light shine through glass. (This works well at the top and bottom of your room; my example shines through both the top, and bottom of the wooden wall, I just used water instead of glass on the bottom.)
Note: This is the piehole texture pack; the yellow stuff is glowstone.