An interesting entry on "Standard illuminant" can be found at
http://en.wikipedia.org/wiki/Standard_illuminant.
In the context of this thread, the following quote from this article may be helpful.
"Illuminants B and C
Illuminants B and C are daylight simulators. They are derived from Illuminant A by using a liquid filters. B served as a representative of noon sunlight, with a correlated color temperature (CCT) of 4874 K, while C represented average day light with a CCT of 6774 K. They are poor approximations of any common light source and deprecated in favor of the D series.
"Illuminant series D
See also: D65
Relative spectral power distribution of illuminant D and a black body of the same correlated color temperature, normalized about 560nm.
Derived by Judd, MacAdam, and Wyszecki, the D series of illuminants are constructed to represent natural daylight. They are difficult to produce artificially, but are easy to characterize mathematically."