What makes you say this? I've literally only heard the opposite.
I don't agree either. And I am about to set up a 3x3 tent with my
sun system LEC and a 3100k Phillips bulb for a full run.
I have found the 315 (single lamp) not as effective for flowering as either my 600
Hortilux Super hps or my 600
Hortilux blue mh.
I am using the pair of 600 1 of each hps and mh for the summer freeing up my 315 LEC for a full run test.
However I believe all this proves is the old adage about nothing trumping lumens. Plants mostly convert photosynthesis to the strongest available spectrum.
And the 3100k bulb has the highest par too. The plants respond more readily to the red spike it has over the 4200k bulb.
I don't have the data handy but this was all fully tested by cycloptics when they chose Phillips bulbs. And also the university of Utah which I go I prompted cycloptics to get the cmh going.
I have been testing in my perpetual for about 8 months now a plant at a time or pairs of clones. I have a staggered weekly to bi-weekly harvest and planting/cutting.
Here is the room with all 3 different bulbs going.