Hi!

As far as I know, there is no limit to the number of lights you can have in a scene.  I've seen global light sets that use 30 or more lights in them.

You may want to check the materials on the door, make sure it isn't using any refraction or transparency that is allowing the lights to shine through it.

Also, if you're using the Firefly renderer, you may want to try using the P4 renderer just to see what it  looks like.  I've had times where light would shine through in odd places using Firefly, but it didn't with the P4 renderer.

Good luck!