Many questions have been presented to the staff at X-Rite as to the meaning and application of the various standard illuminants referred to in an X-Rite Spectrophotometer. This document attempts to help our customers properly understand and apply illuminants when controlling color.
To understand an illuminant it is necessary to first understand how we describe light. Light is described for our purposes by what is called a spectral power distribution curve. A specific type of light will emit different amounts of energy at each part of the visual spectrum. The graph of this power emittance over the visual spectrum is called the relative power distribution curve for that specific illuminant or source.