Thanks @Hellraiser
Autos can survive on any light scedule you give them, however I recommend a 20/4.
A while ago there was a group poll over on autoflower network and it showed 20/4 is the most popular light scedule with 18/6 in 2nd.
The comments section was full of people who have tried to run 24/0 but the majority of those that grow that scedule on multiple grows with different plants noticed that deficiencies were more common.
A light scedule won’t effect the yeild, the amount of light in a 24hr period will and that is why we focus on measuring light in Daily light interval, aka DLI, I have written a guide on this topic here.
Many people require 20hr of light to get ideal DLI when they don’t have top of the line lights, and others in cold climates prefer it because it’s proving heat (like in your and my situation) but there is no difference to the auto be the light be 12hr or 20hr if the DLI is the same and the environment remains ideal.
An ideal environment in all aspects greatly effects growth and yeild, ideally day Temps should be 79f this has been the optimal growth temp range as determed by Utah state cannabis study with Dr. Bruce Bugbee.
Keeping the humidity ideal for that temperature and the growth state of the plant is where your vapor density chart comes into play, cannabis VPD chart. This is a good guide but using a laser temp gun and inputing your own into a custom VPD chart depending on leaf temperature difference to air temperature is ideal (but not needed)
The best way to control this is with a AC infinity exhaust fan and using one of their controllers, setting the values. If you don’t have an AC infinity then you can buy an inkbird temp sensor and plug it into your exhaust fan.
Then get a modern humidfior that has a humidity sensor and values built in so you can set your humidity to 70% or whatever is recommended by the VPD chart.
In a colder environment it’s important to keep the plants and pots off a cold floor so use a riser of some sort.
A space heater will go along way in growth of your plant, I would set it for the same times as lights on, timer, but then have it shut off Durring lights off.
Lower Temps at night will help mildly stress the plant and produce better terpenes and canaboid levels.
I’m in agreement with everything @Not2SureYet is saying, as he said we learn from each other as we have both had a passion for autos for years and for the most part we see eye to eye on things. We each have our own ways on certain things, and finding what works for you is always best. I try to give values to everything that have been backed by research or vast amounts of user input and experience (in the lack of available research) as this helps new growers go shoot for an ideal and get as close as they can while learning what they can and can’t make work for them.
-Nicky