Light cycles for autos

Hey guys…just wondering if ,now that my autoflowers have started to turn to bud on a 19 hour cycle if I should start to reduce the daylight hours down to around 14 hours a day to assist things along…??

And should I be just as super careful not to expose my flowering autos to any unwanted light when they are resting???

Thanks for taking the time to read my questions…any help or suggestions is greatly appreciated and respected…

Cheers people…HAPPY Growing…

I have seen people here grow autos from 12/12 to 24/0 light schedules.
I am currently using a 18/6 schedule to give them some rest.
Its not critical to block all light with autos like photo period plants.

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I go with 12/12 saves on the energy bill later.


First grow going 12-12. Have 2 photoperiods. Autos seem to do well with it.


Depends on your lights and how much they can deliver the needed photons to feed the plant with the needed Daily Light Integral.

With powerful lights that deliver the needed PPFD for flowering of between 500 and 800 PPFD without using supplemental C02 you’ll want to calculate your DLI and see how many hours you should keep lights on in order to get the most growth from your ladies with the light/s you have.

Using the less expensive LUX meter and using their conversion calculator you can determine what your PPFD is and then calculate your DLI based on stage of growth.
HLG 260XL fixture with a reading of 40,000 lux (using lux meter or I also hear they have phone apps) is equivalent to 583 PPFD
583 x 3600 (seconds in an hour) = 2,098,800 then multiply that by the number of hours your light is on (say 12 hours) = 25,185,600 then divide this by 1,000,000 (or just move the decimal point over 6 places) and you get a DLI of 25.1856

If your target DLI is say 40 per day than you’ll either need to move lights closer to plants (increases your LUX and in turn the PPFD) or increase the hours they are on Per day or get better lights that can reach the needed PPFD.

Here are some charts and some links to help better explain this stuff as there is a lot but once you’ve looked through things it becomes clearer.

This may be more than you wanted but if you’ll be doing this for a while it will be something you’ll eventually want to understand.

I just went through the process of figuring out how long to have my lights on in my Auto grow tent as well as my Photo grow tent.

Hope this helps




You should check out “how to grow a monster post” for more brain melting but excitement :slight_smile:


I agree mate…how long do you think he has worked for the lighting company??Thank you to you and everybody else who responded…I have dropped them down to 14 hours now,

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I think @HornHead has great results with autos. Don’t quote me, but I think he does 24 hrs 1-2 weeks, drops 18/6 for a couple more during veg, and then flips to 12/12. I plan to follow this technique with my grow that started a couple weeks ago. So far so good. Hoping to reduce electricity cost. Approximately costing me $100 a month for my lights since starting indoor (using optic 6 led) but about to purchase Growers Choice ROI-E680 with controller. Good luck bro, you are definitely in the right place for tons of info and direction.


@Skydiver great post, this was just something that I was hearing about and hadn’t done the homework on the DFI yet.

@downunderdude that being said until you do the math stick to 20/4 or 18/6, again this would depend on your lighting quality and your budget. If you have good top end lighting go for a 18/6 if you don’t go for 20/4.

24/0 is a waste and most long time auto growers have noticed that more issues tend to happen when on this schedule, cal and mag deficiencies etc.

when you do the math running a grow at 24/0 vs 18/6 the realization that you could have paid to power another full grow yet have no increase in yeild.
People are still learning alot about autos and myths are being dispelled such as you shouldn’t top them and that they do best on 24/0.

Most of the top growers on autoflower network do not run 24/0.


@VTGROW kind of off topic, I apologize. But did you end up getting that roi 680? If so, how are you liking it?
I’m looking to replace my lights this week. And have it narrowed down to a few, Growers Choice roi 680 being one of them.


No I actually went with Optic. Here’s the link to my thread, check it out. ROI controller might have more options but optic slim LEDS are warrantied 10 years and driver for life.

New larger grow room almost complete! - #35 by VTGROW


Thank you, checking it out along with those lights!

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Late reply, you probably won’t see this but the information is much appreciated. :pray: