Ideal Lighting Cycle for Autos?

You’re right—although autoflowering cannabis plants can be grown under 24 hours of continuous light (24/0), it’s generally not considered ideal. Most growers have found that autoflowers perform best under a lighting schedule of either 18 hours of light followed by 6 hours of darkness (18/6) or 20 hours of light followed by 4 hours of darkness (20/4). Cannabis plants, even autoflowers, benefit from having some darkness each day. During these dark periods, plants perform important metabolic processes that support overall growth and health, including root development and nutrient uptake. Without a dark cycle, plants may experience unnecessary stress, slower growth, and reduced overall vigor. A lighting schedule like 18/6 or 20/4 offers a good balance—maximizing growth with ample photosynthesis during the day, while also allowing essential recovery and metabolic processes during the short nighttime period. Between these two options, many growers prefer 20/4 for autoflowers to squeeze in a bit more growth potential without significantly sacrificing rest. If you’re currently running 24/0, consider transitioning to either 20/4 or 18/6. This often results in healthier, more vigorous plants, and ultimately, better yields and quality. Hope this helps your grow buddy!

Proper dli with 'enough' darkness. More hours of light does not necessarily mean more yield. Your environment creates a ceiling for photosynthesis, which limits how much DLI you can provide each day without damaging the plant. 18/6? 16/8? irrelevant if you are giving the same DLI. I wouldn't go more than 18hours/day of light unless your light is incredibly underpowered and the boost to DLI outweighs the lack of a dark cycle. "Dark cycle processes" can and do occur in the light, so 24/0 can work okay but not ideal. Also, irrelevant whether you are growing autoflowers or photoperiods outside of a long enough dark cycle causing flower phase for photoperiods. Both can handle the same levels of DLI. It's just a subspecies or variant and not that much different otherwise. I feed autos the same exact way i feed photos. I provide light the same exact way with same power and distance hung. they react the same way, grow the same way etc etc. I love the fact that people think they are faster, and the businesses that gladly take advantage of that misunderstanding, lol. 14-16 weeks for a small plant isn't faster.

m0use really expounded on the topic well, I concur with the DLI approach (in fact I have some diaries that take the DLI approach to light delivery and take it to extremes, like 8 hours on 16 hours off; the DLI approach has never been wrong yet). theoretically if you could have the plant ready to receive the DLI and could safely deliver the entire day's worth of light in a single second, then you'd be growing top shelf gas god level fuego with a 23 hour 59 minute and 59 second night cycle; this same exact math is the reason why 9/10 homegrowers (in a wildly generous estimate) using CO2 are wasting their time and money we often forget that the plant conducts activities at night... a 24 hour light cycle with no break is always wrong. the plant will try to establish a rhythm and will be stressed; this is also why pure darkness at the end of the grow is 100% grow-bro-science (the plant will still behave according to the established cadence and nutrient transport will still occur in the would-have-been daytime as if during the day, much like other species and their circadian rhythm) IME as long as your lights math right, the best flowers I grow are with the longest night periods

different lighting cycles have been around from the beginning of time. They almost all miss the bottom line of DLI. The whole thing about growing indoors is to mimic to the best ability the environment it normally grows in, and then from there you can alter it to maximize somethings but still need to do it within the plants tollerance. 20/4 24/0 18/6 16/8 all these lighting times can have the same effect on the plant in terms of engery delivered to the plant. in the plant world they call it the DLI. its about lights intensity over time in a 24hr period. Most growers do 18/6 for veg and 12/12 for flower in photoperoids or 18/6 veg to flower in autos. With my lights I would fry them as they are bit overpowered for my setup. So i have to do 16/8 at 40% dim and 20" hang-height to get a DLI of 37.5 the max DLI is around 40. above 40 you need to supply more CO2, water and nutrients in the right ratios and keep the temps and RH on point. if not it gets hurt. If my plants where at 12" vs 20 the DLI would spike way above 40 and I'd run into issues even at 40% dim. With all this in mind, you can have the same DLI on all the light cycles mentioned above by changing hang heights and dim settings as that controls the intensity of the light. When lights are closer to the plants they are stronger and when lights are not dimmed at all and at 100% they are stronger. The one thing people don't think to much about is the down time that plants need. They do things in this off time like we do in our sleep. Its why people refer to 24/0 as bad as it does not allow the plants any downtime/sleep. I like to have min 6hrs ideal 8hrs down time for my plants, and as long as it hits that and my DLI is on point 30-40 I'm golden. First figure out what your lights PPFD maps are, and then calculate its estimated DLI. https://www.waveformlighting.com/horticulture/daily-light-integral-dli-calculator I'd also susgest reading up a bit on DLI and PPFD, some good videos about it with dr.brucebugbee on youtube. he studies light and with regards to cannabis. As a ballpark. most common lights are desgined to be hung 12-18" above the canopy and ran at 18/6 12/12 cycles. So if anything. go down to 18/6 at 18" and then adjust as needed. The plant will tell you if its to little or to much. To little = stretching to much = compact grown and no stretching Can get confuseing when growing multiple strains as some will be compact and some will be stretchy regardless.

I'd say 1st 2 weeks go 20/4 then 18/6 for the rest of its life. Autos like most plants still need a rest period.

Yes the most standard Cycle is 18/6 but also 20/4 is possible.

20/4 works good if the plants get stressed go to a 18/6