The Ishihara 38-plate test is the standard diagnostic tool for detecting color blindness. The test contains 38 circles with patterns created by sets of irregularly shaped dots in two or more colors. The Farnsworth Lantern test is used for more critical testing applications, such as those for aviation, maritime and railway jobs, where the determination of color is necessary for safety in reading signals. The test uses nine different pairs of colored lights in red, green and yellow-white combinations.
The Ishihara test is often used to detect deuteranopia, which is red-green color blindness and by far the most common in the occurrence of color-related visual impairment. Color blindness can be difficult to detect, especially in children, because most people are taught the color of things at a young age, such as grass is green, and don't realize they have a problem seeing color correctly. The Ishihara test is designed to be distributed in booklet form and can be easily administered by an optometrist.
The Lantern test is more difficult to administer, and errors in its administration frequently occur when it is not given in the correct lighting, at the proper distance or with the right timing. It was originally designed for the U.S. Navy to determine the ability of sailors to discern signal light colors at night.