"McAdam's ellipse" is a very important term in the field of lighting, but many lighting people have a wrong understanding of it. The definition and introduction of McAdam's ellipse are not very accurate in many articles. For example about some science: "1942 scientists MAC Adam use this principle to 25 color experiment, in each color point approximately 5 to 9 in the lateral direction measurement, record it just able to discern the color difference of two distance, the result is some different size, the minor axis of ellipse, called mike Adam ellipse", actually this is not the correct definition. According to Visual Sensitivities to Color Differences in Daylight, published by David L. MacAdam in 1942, in the experiment of Color matching, Changes in each direction on color matching the experimental results of the standard deviation (color matching variation standard deviation) set color wide capacity and is not Just perceived Difference (Just Noticeable Difference, can also be translated first distinguishes the Difference) determine the boundary of the ellipse. The reason for this is to avoid observing the irrational effects of fluctuations. The McAdam ellipse is the standard deviation, not the color difference, but the color resolution. In this paper, McAdam proved through experiments that there is a linear relationship between the detected chromatic aberration and the standard deviation corresponding to the color matching, and 3 times of the standard deviation is the detected chromatic aberration.