of course shortening the light schedule will affect the growth, it will grow slower for sure you're at 19hrs right if you go less than 10 hours maybe like 8 or 6 or 4 hours you'll see a pretty huge difference. if you're at 18 and go down to 16 you wont notice much. the only thing about light is that it litterally burns off the THC and the terpenes produced by the plant, both of these are highly sensitive to light. What i'm going to do is reduce the light schedule around harvest time so the plant can really fill out with taste and potency. So in other words yes, light is a big deal and will affect growth - hope this helps ! 🚀