The early instrumental methods for color measurement are based on transmission or reflection spectrophotometry. The concepts were based on research by the physiologists who developed the responses of the cones in the human eye in terms of the visible spectrum. They were able to do this in a manner easily reproducible in the laboratory today. Three projectors are required, with a red, green, or blue filter in front of the lens. Therefore,we can define spectral color in terms of the amounts of red, green, and blue (RGB)