Final answer:
A person with deuteranopia will need to adjust the yellow brightness on an anomaloscope to match the red and green lights due to their difficulty in distinguishing green light.
Step-by-step explanation:
Anomaloscopes are used to test for color vision deficiencies, such as protanopia and deuteranopia. These deficiencies are types of red-green color blindness. Protanopia is the absence of red cones in the eye, while deuteranopia refers to the absence of green cones. When using an anomaloscope, a person with deuteranopia will need to adjust the yellow brightness, because they cannot distinguish the green light as well as someone with normal vision. They will try to match the brightness of the yellow light to the red and green lights mixed together to appear the same to their eyes. Protanopes, on the other hand, wouldn't adjust the yellow brightness to the same extent because they have difficulty in perceiving red light.