When the test field is set to 87 in the Nagel Anomaloscope, what does this indicate?

In the context of the Nagel Anomaloscope, a test field setting of 87 indicates the brightest setting for the red and green lights presented to the subject during the color-matching task. The purpose of the Nagel Anomaloscope is to evaluate an individual's color vision, specifically in distinguishing between red and green hues.

When the test field is set to 87, it means that the intensity of the light is adjusted to its maximum, which allows for optimal visibility and matching of the colors being tested. This is crucial in evaluating color vision deficiencies, such as those seen in various types of color blindness. The bright setting ensures that the observer has enough contrast and clarity to make accurate assessments regarding color perception.

In contrast, the other choices relate to specific wavelengths or intensity levels that do not align with the action of setting the field to 87 in this context.