Farnsworth D-15 vs FM-100: Which Test Do You Need?

What is the difference between the D-15 and the FM-100?

Both tests come from Dean Farnsworth and both ask you to put colored caps in hue order. The difference is resolution. The D-15 uses big hue steps, so only a significant deficiency scrambles the order — which makes it good at naming the type of a real deficiency and deliberately forgiving of mild ones. The FM-100 uses small hue steps all the way round the color circle, so it grades discrimination on a continuous scale instead of pass or fail. Neither is the most sensitive way to catch a mild red-green deficiency; plate tests are.

Which Farnsworth test do people mean?

Usually one of three. The D-15 (also called the Farnsworth Dichotomous Test) splits people into those with a significant deficiency and those with normal or very mild color vision — the 'dichotomy' in its name. The FM-100 grades fine discrimination on a continuous scale. The Farnsworth Lantern, or FALANT, is unrelated to caps: built for the US Navy in the 1940s, it shows pairs of small red, green or white lights and asks you to name them.

The lantern matters mostly for aviation history now. The FAA removed lantern tests from its list of accepted color vision tests on January 1, 2025, and a lantern needs a calibrated light source, so it cannot be taken online.

Which test should you take?

Start from the question you want answered. To find out whether you are color blind at all, a plate screening such as the color blind test or the Ishihara test is the right first step. If a screening flagged a red-green difference and you want to know which kind, the D-15 is the classic next test, because its confusion axis points one way for protan and another for deutan. If you want a graded measure of fine color discrimination — for curiosity, for work that depends on color judgment, or to compare yourself with people your age — the FM-100 is the one. A normal FM-100 or D-15 result does not rule out a mild red-green deficiency; the plates are more sensitive for that.

For a job, a license or a pilot medical, neither online version counts: those require the specific in-person tests an employer or regulator accepts, such as the ones listed on our FAA color vision test page.

Why can you pass the D-15 but get a high FM-100 score?

Because the D-15 is built to let mild cases through. A person with mild anomalous trichromacy can usually follow its large hue steps, while the FM-100's fine steps can turn the same weakness into extra errors. Neither result is wrong; they measure at different resolutions. The FM-100 is not a reliable detector either: in Jennifer Birch's study of 238 men with inherited color vision deficiency, about half of the anomalous trichromats scored under 100 with no clear confusion axis — results that could pass for normal without a plate test.

Age matters for the FM-100 too. In Kinnear and Sahraie's norms the mean Total Error Score falls from about 364 at age 5 to about 43 at age 19, then rises again to around 150 by the seventies, so a score only means something next to the right age band — see how FM-100 scores are read.

Can you take the D-15 and FM-100 online?

As self-checks, yes. Both are arrangement tasks, so they translate to a screen well, and our versions score them the standard way — the D-15 with the Vingrys and King-Smith method, the FM-100 with the Total Error Score. The catch is color accuracy: an uncalibrated display, a night-mode filter or low brightness shifts the cap colors, and the fine-stepped FM-100 is the more sensitive of the two to that. Treat online results as relative estimates, not a diagnosis.