I think there was a study done MH vs HPS and HPS wins in terms of overall growth. @MIMedGrower i think was the one that informed me about it in random conversation. What i was referring to as you said was node spacing not overall plants size. With a more blue spectrum the internode distance is shortened creating a more compact growth and a more red spectrum resulting in longer internode spacing.
Thats not the same as mh bs hps. Cobs and all “full spectrum white” led’s are actually blue phospher coated. Thats why so many leafy buds under led. They are adding far red (actually red) diodes to compensate now.
And yes the university of michigan did extensive testing and determined faster and more growth using hps the whole cycle.
But that was then with bulbs. Now they are testing discreet colored diodes for perdect crop spectrums.
Nasa has a lot of info on led too.
Here is a reprint (on advanced led site) of Nasa findings. The second section is colors and how they affect plants and how they need to be combined.
So the arbitrary color temp they are putting on full spectrum led’s is not really the same. Example a 2700k or 3000k led is no where near the red output of an hps. The led is far more balanced and leaning to blue.
Eventually we will have a combined blurple with extra green and blue and red designed for specific crops.