Tried the various suggested methods.
The 'Light Inside The Box' didn't work.
The 'Light Shining At The Box' kinda works, but the time involved is very large and the coverage of the light is not quite acceptable (at least until there are rectangular lights).
Anyone have any other tips? Something we've missed? Every other 3D program has the option of an individual object ignoring outside lighting . . . doesn't this program have it?