Can color vision defective subjects who pass the farnsworth lantern test recognize surface color codes?

The International Civil Aviation Organization requires that pilots be able to distinguish the colors used in air navigation and in particular be able to identify the colors of signal lights. Most national aviation authorities use a lantern test to assess the ability of applicants for a pilot's license who have abnormal color vision to recognize the colors of signal lights. However, color-coding is now widely used in aviation systems other than signal lights. Color is used in tarmac markings, maps, manuals, and electronic flight instrument displays. These color codes can use 10 or more colors, many more than the 3 to 5 used for signal lights. This study investigated whether people with defective color vision (DCV) who pass the Farnsworth lantern test can recognize the main colors used for surface color codes.

There were 99 subjects with DCV who were tested using the Optec 900 version of the Farnsworth lantern test and also named the colors of a set of 10 surface colors that varied in shape (dots and lines) and size (3 sizes; angular diameters 0.27, 1.0, and 2.4 degrees; angular widths 0.14, 0.27, and 0.50 degrees). A control group of 20 subjects with normal color vision also named the surface colors.

Of the DCV subjects, 19% passed the Farnsworth lantern test, of whom 74% made no errors with the surface colors. The other 26% made few errors (up to 5 errors in 120 presentations) and those errors were mostly to confuse red, orange, and brown. The subjects with normal color vision made no errors naming the surface colors.

Those who pass the Farnsworth lantern test can recognize the colors of a 10-color surface color code with few or no errors. This is because the small (2.9-min arc) stimulus of the lantern test presents a more difficult task than the larger surface colors.