Imagine that the exact color(say 3000K), is at point X=0.4328 Y=0.4064 on the CIE/blackbody curve. That is "actual 3000K" for this example. Now imagine that is the bulls eye and there are rings that "step" out from that center point. Each ring or step is a deviation away from actual 3000K bullseye.
These "steps" are tiny, and it takes between 2 and 3 steps for humans to see a difference in white light usually, and is very small at best. But what the plant see/think is what matters, and they don''t care...and probably prefer the wider possibilities of more nm's of light from a wide color bin. But really should make 0 difference for the plants.
These McAdams bin steps are for the visual aesthetic world where if a human was walking down a hallway or street...every light/bulb/fixture would appear the exact same color to the eyes. Having a 4500K in a row of 5000K would stand out in a nice building.
Higher step bins are usually cheaper too.
Really doesn't matter, it's up to you and availability of what you can get.
