Definition of simulated instrument conditions

Does anyone know if Simulated Instrument Conditions is defined anywhere?

The reason for the question is whether one can log instrument time, say
at night, when you don't look outside, but don't wear foggles or a hood?

I can't find anything in the rules that defines simulated instrument
conditions, but since the rule for logging instrument time says both
that flight has to be solely by referenct to instruments in actual or
simulated instrument conditions, that would suggest that more is
required than "solely by reference to instruments" and therefore that
some sort of view limiting device is required.

It would certainly be easier if they defined simulated insturment
conditions though.

Brad