HPS Spectral Puzzle

I are an enguneer and am puzzled by the great growth rates provided by HPS.

Yes, I understand that the lumens/watt ratio is very high, but the spectrum seems quite far away from the ideal, with the largest proportion being yellow, which allegedly has little to no affect on chlorophyll A or B production.

Red/Blue LEDs seem to hit the 'sweet' spots with little waste and do just OK.

(Please do not degenerate into yet another HID vs. LED thread. Thanks!)

Now the latest generation LEDs have added either white or orange to fill in some of the spectrum and do better than before, but it seems as if some BIG piece of the puzzle is missing.

How can HPS do so well with very little blue, decent red and huge yellow outputs? Seems there is much more to learn about plant physiology.

hps has more specialized bulbs that provide better color for growing. led is definitely going to be an option in the future but its just way to expensive right now. Another couple years and I think led will be very competitive with hps

I like Ceramic Metal Halide bulbs better than HPS.

I've also used my HPS for vegging, and didn't experience the 'stretch' it supposedly causes (which I was surprised to see) ... the only thing I know about the HPS spectrum, is that it supposedly replicates the late Summer/Fall sun, which is lower in the sky, and filtered thru the atmosphere ... as a photography student, I was taught that the sun's angle, changes its color temperature, etc... dunno if that answered anything, but I have 'happy typing fingers' this morning :D