Yeah, tung oil makes a great finish on wood. I use it on all of the furniture that I build. You can buff a tung oil finish up to a high gloss, but it won't be reflective. I have a reflector inside my hood for this reason.
MrBurns: Sure, just make sure it's sufficiently dry
BONESTOCK: Black absorbs light, just paint the inside of your hood white. You'll never know from the outside and you'll reflect more light into your tank.
If consequence dictate my course of action, then it doesn't matter what's right, it's only wrong if you get caught.....