Another question. 18 /6 or 20/4?

[Greenpassion]

I was just reading a post here where someone who was growing Autos has their plants on a 20-4 schedule. Is that better than 18-6? How does one decide that and what are the effects?

[Toker1]

I decide based on my power bill and ambient temperatures. First of all autos grow and flower independently from the light schedule. I’ve never grown an auto before, but I believe yields are based on light schedule.
So, here is the deal with photoperiod plants. 18-6 is what most growers use. Reason being is you get optimal growth at this range while allowing time for the plant to “rest”. Having the light on 24-7 allows for slightly more grow, but at the expense of wasting light. The plant has to “rest” and will do so even with the lights on. So from a power saving efficiency stand point, there is a diminishing return with 24-7 lighting.

[Toker1]

18-6 is for veg. I didn’t mention flowering. Yes 12-12 is to flower...some people use a diminishing light schedule.
And take a highest yielding plant and only give it 6 hours of light. If yields were the same, wouldn’t everyone be growing on 6 hours of light? Why waste time and $$ on a 12-12 schedule, if yield didn’t depend on it? Yields are based on how much energy the plant can manufacture. Plant energy comes from light. So yes, light schedule is indirectly responsible for total yield in a grow. There are no short cuts but if you think you can pull the same yield off 6 hours of light vs 12 hours, I must congratulate you because you have just redefined what is physically possible in nature.

[Canuck147]

Did anyone say anything about running lights on a 6/18 schedule?
I use 20/4 myself - if you want to double your yields use a product called 'Foliar Essence'

[Toker1]

I remember someone mentioning that light schedule was independent of yield. I suggested the 6 hours of light as an experiment to test that hypothesis. I already know what the results will be.

[Weed Pharma]

I agree with above and will just state what I do for all auto's, after research/testing all sorts of ideas.

The cost to benefit loss begins at 17.5/6.5 (hence the 18/6 standard) and certainly 24/0 is not cost effective for my low cost per gram setup.

I run LED's at 24/0 until the plant reaches the 4-5th node, then I run 20/4 until harvest.

[DrPhoton]

Yes, it appears to be due to sink/source activity where the sink cannot process photosynthates fast enough and slows down phloem loading in leaves. Ultimately limiting photosynthesis due to photochemical quenching.

[DrPhoton]

I have an article on the subject, might be worth a read.