Color: An Introduction to Practice and Principles, 3rd Edition

6

Defining the Color Stimulus

That there is a significant relationship between color stimulus and our color experiences is a reasonable assumption. It follows general experiences we have that indicate reactions are immediately due to certain actions, and in many cases they are. However, in case of color perception, the action is contact of quanta of light with cone cells, and the reaction is a subconscious and conscious interpretation of the scene in front of our eyes with a very complex but sufficient apparatus supporting our survival. There are countless examples known indicating that there is no simple one-to-one relationship between stimulus and experience.

Color technology has learned that by simplifying the total stimulus as much as possible, a useful degree of correlation between stimulus and response can be obtained, that is, when surround, illumination, and test procedure are controlled, and data for an average observer are determined. This is the basis of the (limited) success achieved in this field.

On the simplest level, the physical stimulus from a light is defined by its spectral power distribution (SPD) and its intensity. SPDs are numbers or their graphic plots representing the power of a broadband light source at a given wavelength, usually relative to its power at 555 nm = 100. The unit of radiant power or energy is the joule or the watt. Radiant intensity is expressed ...