The Light falloff possibilities has been improved in Blender 2.46, at least for the Lamp and Spot lamps. There are now two main controls: the Sphere button, and a drop-down list, proposing different light falloff types, as described in this tutorial..
Let’s assume you have a scene ready, and that you want to render it with the Radiosity Rendering. The first thing to grasp when doing Radiosity is that no Lamps are necessary, but some meshes with an Emit material property greater than zero are required, since these will be the light sources. Emit is found on the Shaders panel in the bottom right (Material sub-context). Typically, a value of 0.5 or less gives a soft radiance.
The Lamp lamp is an omni-directional point of light, that is, a point radiating the same amount of light in all directions. It’s visualized by a plain, circled dot, (Lamp Light).