first grow with it i switched from hps to led 3rd flowering weeks, @100% @25 cm from the plants tops, didn't notice any signifiant differences with last two week of stretch, and in the end i think my bud were slighty more dense and compact in average over the whole plant than with the HPS.
second grow i started with the led @100% @80 cm from plant (my hps 250w routine was @70cm) letting the plant grow without moving the lamp until distance between led and plants tops become smaller than 25cm
third grow i started with the led @85cm @50% first week and half then switched to 75% on going
fourth grow is from my padawan @80cm @60% for 1 week then @100cm @60% for 3 week then 80% @70cm for two first week of flo, then 100% @30cm from plant top
for the three last grow even with different dimming set up we didn't really notice some difference with growth rate between led grows, amount of leaves stage produced in said amount of days but there still the difference with the HPS, the plants seem to produce more leaves stage faster than with LED.
the fact is with hps i was vegging depending strain 2-4 weeks most of the time 3 before 12/12 flip
and now with the LED so far all plant needed 4 weeks before being ready for 12/12 flip
and my concern is gr/w/m²/"weeks spent veg+flo" one week more before harvest do impact this ratio.
also out of 3 grow and half so far with LED we already had a nice dispersion in plant growth in term of height depending strain reaching in the end of flowering 50cm to 1m20 depending strains and phenotypes wich is the same dispersion we had with the HPS, but veg seem slower with led than with hps
also i m wondering a lot on growdiaries.com and i always found that plant from other people with led were smaller than mine under hps at the same stage, not much sometime but still noticeably enough