The plates are carefully standardised and make an expensive book. Like all tests for colour vision and discrimination they must be administered under standard lighting conditions, particularly where the results have implications such as in occupational medicine. The lantern test is the gold standard.
A demonstration of Ishihara testing online can be found at  but it should NOT be used for diagnostic purposes as colour reproduction varies so much between monitors .
Bulbs of various standardised colours and intensities are exposed through apertures of standard size and the subject invited to distinguish them. For the airman or seaman the ability to distinguish faint red from green lights is more important than for most, and several grades of colour vision are given accordingly.