I was not going to comment on this thread about what gun to choose for shooting somebody.
I don't enjoy the question and I usually end up getting flamed by people who think you need bigger and bigger guns.
Bigger is not always better.

OK, here goes

#6 birdshot or smaller might not be heavy enough.

You start getting into trap and skeet loads and they might not have enough power to get through a heavy jacket and sweater.

#2 buckshot in a low recoil load (read lower power) was originally produced at police request just for the problem you describe. It has an effective range out to 25 yards instead of the hunting load's 50 yards, and is supposed to be stopped after one interior partition, but often get through 2. Box of Truth misses on this a bit because they don't have their sheets of gypsum board separated by the width of a room like 2 partitions would be.
You shouldn't need to shoot 25 yards (75 feet) in a home defense.
Anything larger like hunting loads on 00 buck or slug are simply overkill that puts innocent bystanders at risk.

You are right about birdshot from #4 up being effective at the ranges you need, likely less than 3 yards, certainly not more than 10 yards.
As you know, the lighter the shot the faster it loses power over distance.
Most light birdshot (<#6)has lost enough power to be nonlethal at 10 yards (30 feet)

Now about the tacticool stuff.
It seems most house invasions are either in the day when they are not expecting you to be home, or at night and they turn the lights on anyhow.
(Only the most retarded burgler would stumble around in the dark trying to steal what he can't even see.
If the lights are not on it is more likely one of your own kids trying to sneak out or back home without waking you up.)
If they didn't turn the lights on, then you should.
Besides, if you shoot in the dark you will likely end up blinded by the muzzle flash anyhow.

If it is a burgler and they are armed, and you expect them to shoot, then a flashlight on your gun just makes a real good target for them to shoot at.

Finally, if you shoot somebody inside your home you had better be ready to explain it to a judge. The more your home defense weapon looks like a wannabe military assault weapon the harder time you will have explaining.


Somebody mentioned that if recoil really bothers you a 16 gauge could be an option.
A nice innocent looking 16 gauge loaded with heavier birdshot (magnums?) or light buck, (like you might use at the trap range or for hunting) might be a bit easier to explain in court.

A shorter barrel is a nice thing too. Still long enough to point well and short enough to be easy to use in a house.

You should also consider spending a bit of time at the skeet range. The distance you shoot for skeet is more like what you need than traps and you need to get on target fast to hit skeet.