The Web Driver uses vertex lighting, which means that lighting calculations are only done for each vertex of geometry. Once a lighting value is calculated for a vertex, the lighting values of the mesh in places between the vertices are determined by simply blending the lighting from vertex to vertex.
So, there are two things to keep in mind when designing your scene:
Great, that always seems to be the trade-off! In the scene above, use the arrow keys to move the spotlight around above the floor. You can choose the detail of the floor geometry with the drop-down box and play around with the other options by using the checkboxes.
We usually use a spotlight to demonstrate this because of an interesting problem. Try setting the mesh resolution to "coarse" and notice that with the spotlight in some locations, it doesn't even affect the floor! That's because the cone of light doesn't hit a single vertex.
In fact, you may have noticed that by default, the spot lighting looks just plain nasty. That's because a default spotlight has the umbra (inner cone) angle set to the same value as the penumbra (outer cone) angle. This results in a sharp transition outside the cone, which is no good even when your mesh is fine. To fix it, give it a little penumbra (use the checkbox) to blend the light intensity out from the inner cone to the outer.
WT::createLight, WTLight::setPenumbra