If the WPG is not really a concern...and only the K is concerned
These are both untrue statements, so don't get confused again. Wattage is still a concern
but WPG is not really the best way to look at things. It's just a generic guideline people use for lack of anything better. And saying that only the K is concerned is also very false, because even if you have the correct spectrum, what does it matter if the light doesn't reach the plants because it's too low of a wattage?