Is it possible for light sources in Cycles to have nonphysical falloff like in BI? In BI, we have the traditional OpenGL choices of constant, linear and 1&frasl;distance2 falloff, along with some parameters to tweak the falloff formula.  This allowed for a variety of artistic styles, and getting even illumination from lamps that couldn't be put far away.

Cycles is more physically realistic.  What about 3D works in which we don't want such great realism?  Is there a way to make all the light paths between two objects, or between one object and all others, obey alternative laws of radiation physics?
Yes. There is a node called Light Falloff
you can plug in to the Emission shader strength.
It has three outputs: quadratic or Linear
or Constant You my even do some math with the ray
length and plug the result in the Light Falloff
node strength and use the Constant output.
The example is only a demonstration nothing useful.