Walstad notes in her book that plants mainly utilize light at 5600 K for photosynthesis.you may need more watts of "balanced light" than you would if you only used "dedicated plant lights at 5600 K."
Not really intending on arguing that point but it's a bit generic..
5600k led "whites" is not in any sense equal to 5600k "black body' emission spectrum..
Neither is florescent or metal halides..
Only incandescent types can do this
Even mixing RGB you can create 5600k light .
That is CCT more specifically which is an artificial way of producing a "K" temp...
Easiest way is to couple the CCT and CRI (using d50 or d65 as a reference source) to get you closer to a true 5600k temp.
Shift to smaller emitters occurred mostly due to the fact that research pushed efficiencies so the small emitters watt for watt produced more photons/unit of energy than the bigger 3w-ers.
Then there are COBS which are just many small emitters in a tight package..
It now probably only takes 2-3 1/2W led's to do the work of one old 3W-er, which are rarely driven at 3w's anyways.
Ther is still a place for them since they are easily lensed so to collimate the already tight spread (in comparison to competing technologies) which will push more light deeper than larger
angle small emitters. Currently only know of one light that is small emitters w/ 90 degree reflectors..
all part of the geometry of light moreso than the photons..
One only needs to look to hort. lights which attempt (still young) to maximize output at the expense of any resemblance to daylight K values or CRI to understand that yes best light can b ugly light aesthetically but it also is not in any way a "k" light..
Pure red and pure blue diodes are very high in usable photons w/ little to no waste so throwing those in a "white" diode fixture is always beneficial in a photosynthesis sense.. being close to 100% PUR (photo synthetically usable radiation).
Design a light around the above action spectrums and I guarantee neither will be near 5600k.
"crop plant" could be around 4000k
For example, growers have found greater success growing a young plant under cool white 6K lamps all the way through a growth (vegetative) cycle, then switching to a 2K lamp to flower or fruit, and finally finishing the growth cycle using a 10K lamp for the final 2-3 weeks. This has shown to generate better results compared to growing under a single colour spectrum / colour temperature.
When using different lamps with different colour temperatures for plant growth, it is important to keep in mind that the colour temperature rating should be used as a general guide for the approximate colour spectrum that will be produced by the lamp, the actual colour spectrum is what you should look for when choosing your light. The Colour Temperature will tell you the range of colours the lamp will produce, but not the exact amount of each colour produced within that range.
now to add to the complication.. photosynthesis is not the only consideration..