At what key is a whistle considered "LOW"?

I know a high D whistle is considered normal or high.  And a low D whistle is considered 'low'.

Is there an official key where a whistle switches over to being described as a 'low whistle' ?  Or is that just based on people's various views?  Or, is it based only on being clear in describing the whistle? -(as in differentiating a regular C whistle from an octave lower "low C" whistle?