Why did HunterLab chose to use a Green tile instead of a different color like yellow or blue
The spectral range that is weighted for the calculation of the human tristimulus values is 360nm to 780nm, the center of this range is 570nm. L* for non-fluorescent objects varies from 0 to 100, the center of this range is 50. If a user could pick only one specimen to use for a Diagnostic check then if would be ideal if that object had a wavelength peak at 570nm and an L* of 50, which would represent the center of the measurement range. The green tile that HunterLab supplies nominally has a wavelength peak at 530nm and an L* in the range of 50 to 55, this Green tile represents approximately the center of the color measurement range.
The customer is free to choose additional tiles to expand the Diagnostic tests. HunterLab sells a variety of different colors in 108mm x 108mm porcelain enameled steel.