Formation of the Color Impression
The color impression an observer gets from a sample depends on three interrelated factors.
1. Light source
Different light sources (e.g. daylight, incandescent lamp) have different spectral power distributions ( Color and intensity) and thus generate a different illumination of the sample.
2. Sample
The composition of the sample is crucial for determining the fractions of absorption, transmission, and reflection of the incident light from the light source. Accordingly, the spectral composition of the reflected and/or transmitted light that ultimately reaches the eye of the observer is changed by the sample.
3. Observer
Due to the difference in the sensitivity of the three light-sensitive receptors in the retina, even normal-sighted individual observers have slightly varying color perception. In order to determine an objective measure of the spectral change due to the sample (i.e. the "color effect" of the sample), the influence of both illumination and individual observer needs to be determined.
For this purpose, standard illuminants and two defined "standard observers" have been defined on an international level. Accordingly, all calculated color values should be reference these factors based on their standardized derivation. For this reason, objective color numbers always need to be accompanied by specification of the standard illuminant and standard observer for which the color values are to be calculated. This is usually done by means of a corresponding setting in the software of the device.