Hey pall,i did some research on your question on some Dutch grow sites..they advice metal Halide or led of the blue kind like a vegetator from kind leds..anything with a light spectrum between 4000 and 6500 should be good
When a plant is growing outdoors the first months you will see her internodes are e bit longer then when she stretches,in stretch she starts stacking nodes because this is the place the buds will grow for reproduction.this is because in the first months till July the spectrum what penetrates the atmosphere is more blueish due to the stance of the sun
Once past mid August the spectrum is more red
This is why many commercial growers keep 20-30 mothers in 1 room under just 1 1000w mh on a light rail
I experienced on my side the benefit of growing solo hps because my plants stay really short in veg but with lots of nodes stacked on each other
Ideal when growing in a low basement