What does a value of 0 represent in the test field of the Nagel Anomaloscope?

In the context of the Nagel Anomaloscope, a value of 0 represents the dimmest setting. This instrument is designed to assess color vision and specifically evaluates the ability to match colors through the mixing of two wavelengths of light.

At the lower end of the scale (0), the comparison light is set to its minimum intensity, allowing the subject to perceive the dimmest light possible in the test. In this state, it tests the observer's sensitivity to low levels of brightness and the ability to distinguish color hues when they are presented faintly. As the settings increase from 0, the intensity of the comparison light increases, leading to brighter settings. Understanding this scale is crucial for interpreting the results of color vision testing and identifying potential color vision deficiencies.