Point lighting works by interpolating the colour value across a triangle poly. If your floor is not split, or tescalated with smaller triangles, your floor will not show proper light illumination, see the following diagrams to see what I mean.
In the first diagram, this may represent what your floor comprises of now:
Where as this is what a point light floor must look like:
If you adjust your floor to consist of more triangles, your point light should work more realistically.
[EDIT] This thread may interest you also. Something I did ages ago to demonstrate a torch effect using a light.
http://forum.thegamecreators.com/?m=forum_view&t=94793&b=1
Paul.