Hardware lighting shines through walls?

Create a prim and assign a nice strong light to it.
Build 5 walls around the prim.

The hardware lighting does not understand that the light coming from the 'radiant' prim should be blocked by the walls.

Why is this? This seems broken to me.

Apparently this is how it works.... Something to do with Ray Tracing not being used..

I think it works by lighting any surface within range that faces the light, the lack of Ray Tracing means the surfaces aren't aware of other objects in between so they are rendered lit anyway..

Don't know how to work around it... sorry..

Yes it has to do with the fact that computer games are still rendered using the much faster polygon rendering techniques that provide a reasonable approximation but will have a good number of flaws.

Not blocking lighting is one of them. A light source in SL will light all polygons untill the intensity has "fallen off" (falloff) due to distance.

Quick workarounds include moving the light source farther or adjusting the radius and falloff parameters.

There is an approach involving black colored light but you have to use that sparingly because I hear only the 6 nearest light sources get rendered by the client.

There are polygon rendeing techniques that do fairly accurate shadows but SL is not using them and using them will slow down our clients by a factor of maybe 3 or 4.