The MacAdam ellipses, or SDCM (standard deviation of color matching), are standard deviations of perceived color differences in LED binning including white LEDs. The higher the step or standard deviation, the lower the binning tolerances which lowers LED costs.
MacAdam Ellipses steps illustration
Methodology was created by MacAdam in 1943 for mathematically constructing ellipses about target points. The goal of the research was to determine a series of boundaries around several color targets (x, y coordinate) on the CIE chromaticity diagram, illustrating how much one can 'stray' from the target (along various color axes) before perceiving a difference from the target color. Any point on the boundary of a '1-step” ellipse, drawn around a target, represents 1 standard deviation from the target. ANSI recommends that lamp manufacturers stay within a '4-step” ellipse. This means that, given a certain target point on the CIE diagram, lamp manufacturers are given a fairly wide range of perceptible differences. Sylvania, What are MacAdam Ellipses or color ovals?
To make it simple and practical, only in a 1-step MacAdam ellipse for white LEDs are any variations in the white light unperceived to most people. In a 2-step MacAdam ellipse variations may just be perceivable to a trained eye, and in a 3-step MacAdam ellipse variations may be just perceivable to an untrained eye
With LED grow lights we don't really care about minor variations in light, and the Samsung LM301H (horticulture) series of medium power LEDs use a 5-step MacAdam ellipse binning, while the LM301B (general illumination) uses a 3-step. In other words, the LM301H has a lot more binning slop that is basically irrelevant to plant growth, but could be relevant for general illumination. The highest MacAdam step number used with LEDs is seven.
In conclusion: don't worry if you can perceive slight color differences in the LEDs of LED grow lights! Your plants don't care.