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.
RackitMan Reviewed by RackitMan on . 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 Rating: 5