The lantern has been used since Dean Farnsworth first described it in 1946 for the testing the color signal discrimination ability of color anomalous individuals. This test has found longstanding application in the military and the transportation industry to qualify operators of ships vehicles and aircraft that are known to have failed screening tests such as the Ishihara plates.
Because many color deficient persons do have reasonably good signal light discrimination, this test often justifies the employment of these individuals. The original test device has long since stopped being manufactured and more modern equivalents are quite expensive for the limited usage they see in a typical optometrists office. This has resulted in prospective patients often traveling long distances for the test.
The Farnsworth Lantern Flashlight comes with batteries and a xenon bulb.