If using LED lights 4 hours of darkness is better for the autoflowering weed than the non-stop light. The first pair of leaves looked stressed because of the 24/0 light cycle. The new pair of leaves is looking just fine after introducing the 20/4 light cycle (20 hours lights on, 4 hours lights off).
They’ve never been able to consistently prove anything but a decrease in yield when using a 24/0 light cycle, for a plethora of plants, including cannabis.
At the most, and very rarely, it levels out to roughly the same yield as a 18/6 light cycle for the same time period, in which case all those extra hours on the electricity bill, and the extra hours on the life of the bulbs being used, they go to waste and the crop is more expensive, for no additional gain.
In just one month, that’s an extra 180 hours of bulb-life and electricity cost, that goes down the drain, all for nothing!
A 20/4 light cycle is a good happy medium for autoflowering cannabis plants, but if your ladies are stressed for what appears to be ‘no good reason’ (and some strains are more finicky and more sensitive when it comes to over-exposure to light, than others) then it may be a good idea to cut back a few hours.
Another reason 24/0 became popular is due to new, and inexperienced growers, who learn along the way and improve their yield almost with each harvest. A new grower in my eyes, has anything under 20 successful harvest under his or her belt.. some people grow for a decade, and they’re still modifying and improving their technique!
Many new growers, who are still learning how to treat their plants properly, sometimes improve their own gardening skills while at the same time trying 24/0 lighting for the first time. Sometimes, their yields increase.
But instead of giving credit, where credit is due (in other words, to their savvy and improved growing skills), they instead chalk up this success to the extended light cycle.
The potential for improvement when using 24/0 is a phenomena generally restricted to new growers, due not at all to the light schedule, but to their skills improving; most of us old timers, who’ve already had the environment, feed and care dialed in for several decades, see either a leveling off or a decrease in yield when toying with 24/0.
More info on 24/0 lighting found on forums, if you’re interested in the details:
“They’ve proven time, and time again, that virtually all plants existing naturally under normal daylight-darkness conditions, require a regular, dark rest phase… cannabis is not all that unique in its requirements, compared to other light-sensitive plants that require a specific photo-period to function at their prime.
After years of trial an error, on both cannabis, and a plethora of other flowering and fruit/veg-bearing plants, they’ve consistently determined that you yield the same or less when running 24/0.
Yielding the same doesn’t sound like such a big loss on the surface, but think about it this way: during a month long veg cycle for instance, that’s an extra 180 hours of bulb-life you’re wasting, and electricity cost you’re sacrificing, for no gain (and sometimes, at a loss!).
If you really want to try to stretch the light exposure out, a healthier option is to go for 20/4 during veg, and 13/11 in bloom for the first three or four weeks.
Plants respire and have pores which function, open and close, depending on the light cycle.. if you keep them awake all the time, they become stressed and start losing vigor, and eventually (late-stage) they develop chlorosis.
The ONLY REASON people assume incorrectly that it’s somehow safe or healthy for cannabis, is because the life-cycle we run them through is relatively short, enough so that by the time we flip to 12/12 the damage has been done, but may not be visible to the naked eye.
Just because you visibly don’t see obvious signs of distress, it does not mean your plants aren’t suffering and lacking in vigor and growth-speed.
They’re tough, hardy plants. They can take some abuse! Just because they are still alive, and they appear healthy enough, it does not mean that they are making more progress, and it does not indicate whether or not their development has been crippled.
Prolonged 24/0, besides causing your yield to suffer, can cause a high male count, hermies in otherwise-female weed plants, chlorosis and reduced photosynthesis, and even death.
Rarely, some cannabis strains are much more delicate that others, and may show noticeable, visible damage within the first two weeks of 24/0, while most others can take up to two months or longer before appearing obviously, visibly distressed.
It’s why many auto-flowering cannabis plants, grown from veg through bloom under 24/0, tend to look a bit more stressed out than naturally grown plants by the end, and it’s why they were once known for being low yielders.