Cannabis will flower under almost any white light ,no matter the source (CFL,
HID,LED,etc) and no matter the CCT & CRI .It’s the hours under light vs dark period which induces and promotes flowering and not the light spectrum .
But...
As a crude rule of thumb ,
for cannabis flowering under white light :
The more
blue light contained in the white mix ,
the bud quality tends to increase , but with a negative impact on yield.Only 10-15%
of the total power should be blue light for plant health and vigor .More than that , Blue light effects
will be induced dramatically.
The more green contained in the mix overall yield will increase (as the lower buds will gain more weight ) , but potency will drop ,regarding the production and final concentration of Δ9-THC.
Still , about 25-30% of the power has
to be green light ,for plant health and vigor .More than that ,adverse effects
might be induced ( like shade avoidance syndrome,low potency,slow bud growth rates ,etc).
The more red light contained in the mix ,the more carbohydrates are being
synthesized and more nitrates are being assimilated ,thus yield is affected positively ,regarding mainly top buds ,while overall cannabinoid production is also affected positively.
40-60 % of the white mix ,should be red light ,for productive plant cultivation ....
Far red should be present at very low
quantity ( 2,5-5 % ),due to Emerson effect affecting positively the yield .Also keeps the Pr/Pfr ratio more balanced.
Too much of it ( like with 2700K 90Ra ) ,will cause internodal stretching,shade avoidance syndrome and excessive internal heat. Foxtailing is more likely to occur ,also.
More or less ...
EDIT: You will probably encounter suggestions like “ CCT & CRI are human vision centered metrics ,thus are useless for plant cultivation.“
While this is being generally true ,still
in the phosphor conversion white LED lighting world ,the CCT value represents more or less a certain SPD curve -thus certain standard R-G-B-FR ratios ( phosphor(s) amount ) ,while the CCT value gives away the phosphors used for producing white light out from a monochromatic blue light excitation source (peak: ~ 440-450 nm)...
CRI 70:A single yellow or yellow-green (peak : ~ 560-570 nm) phosphor used.Highest electric efficiency ,but lowest photosynthetic one.Less cooling required.
CRI 80: Blend of a green ( pk :~550 nm ) phosphor with an orange-red one ( peak around 600 nm ) .A balance between electric efficiency & photosynthetic efficiency.
CRI 90 / 90+ : Blend of a green (pk:~550 nm )phosphor with a red one ( peak around 630 nm ) .Highest photosynthetic efficiency ,but lowest electric one .LED devices of high CRI generate more heat,due to higher Stokes shift losses,etc.
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