18 Hour Light Cycle

2 Can · #1 02-06-2009, 04:48 AM

Growing with an 18 hour Day/Night Cycle

The theory behind the 18 hour Day/Night cycle is that during a normal 24 hour light cycle plants will usually achieve high growth rates peaking at 100% capacity during the first 50 - 60% of the day. The growth rates will then diminish rapidly and the last 20 - 30% of the day achieves minimal growth. So by reducing the length of the day we are triggering an increased growth mode where the growth rates are at their peak for the majority of the day. This effectively achieves a very fast growth cycle with full yield potential.

NOTE: To achieve these incredible growth rates it is important to provide maximum light intensities and CO2 enriched conditions. The recommended lighting is 600W per square metre.

The Cycles

Vegetative Cycle -
Lights ON 14 hours
Lights OFF 4 hours

Flowering Cycle -
Lights ON 6 hours
Lights OFF 12 hours

The Benefits

The growth during an 18 hour cycle can be the equivalent to that achieved during a 24 hour cycle. So by running 18 hour cycles the same growth and yield can be achieved in 75% of the time. Reduced day lengths also mean reduced power consumption. Grow more and use less power. Who can argue with that?

For example, an average crop grown from seed using a 24 hour day/night cycle will have a 4 weeks grow cycle and an 8 weeks flower cycle. This equates to 28 days @ 18 hours a day and 56 days @ 12 hours a day = 1176 hours of light over 12 weeks.

An accelerated crop using an 18 hour day/night cycle will achieve the same yields using a 3 week grow cycle and a 6 week flower cycle. This equates to 21 days @ 14 hours a day and 42 days @ 6 hours a day = 546 hours of light over 9 weeks resulting in a 40% reduction in power consumption and a 25% reduction in crop time.

Crop rotations in 7.5 weeks (down from 16weeks)

Getting efficient output is what it’s all about. I have to be at least a little dubious. But try this for size... I have to think that there’s something to it.
All species of plant, insect or animal on earth have their "Day period" during which, their efficiency is greater for SOME of that time. While they can use up to 18hrs of light, maybe for 12 of those, they are at 100%, then drift off to only 60%-70%, then to 20%-30%. Consider... most days we wake up and are at 90% in 5 minutes, at 100% in 10 minutes. After 10/12 hrs, we’re flagging badly and while happy to stay up another 6-8 hrs, are just "laidback". A young kid on the other hand, is at 90% within 10 seconds of waking and 100% in 30 seconds. They hit the wall "like a bird flying into plate glass" after 14 hrs, then sleep like a brick for 10! Others however, take an hour to get to 60%, another hour to get to 90%.

Plants don’t think, they react to a genetic 'drive to survive'. So, I conclude that there is a case to examine where a short day cycle could trip a plant's genetic response into a "survive or die" accelerated mode to flowering and fruiting. The idea is to capture the hours that would give 90% or better, of the plant's "production" but maybe saving 25-30% of the daylight period (power being a special consideration).

Set vegetative cycle at 14hrs day and 4hrs night for an 18hr day
Run it for 7 days (about 10 "plant days") at 2000ppm CO2
That period gives sufficient leaf development to proceed with the flowering phase.
The "Fast Flower" 6hr days and 12hr nights regime lasts 45 days.
Crop is better than EVER had in 16 weeks." Yields?, "I’d say 135-140% of previous best crops.
7weeks and 3 days Harvest. Impressive result. 6 great crops a year, low management of them and every one a winner!

The claims Leaf phase (light hrs) Flowering phase Total

1. Non CO2 4wks (28days @18hrs) ,12wks (84days @12 hrs) =16wks (1512hrs)
378 lights ON hrs/mth.

2. "Short Cycle" 7day (10cycle@14hr), 45day (60days @6 hrs) =7.4wks (500hrs)
Unbelievable result! Easy harvest and growth. 250 lights ON hrs/mth. Great result, especially that the grow room/crop management is also massively reduced.

3. Std CO2 cycle: 2wks (14days @18hrs), 10wks (70days @12 hrs) =12wks (1092hrs)
Fantastic crop. 364 lights ON hrs/mth. Easy harvest. Supporting evidence.
Indicated power usage for the short phase growing cycle reduces to about 250hrs/mth, from 378hrs/mth, a drop of 33%!
Power usage dropped to 66%, a saving of 34% (from $500/mth to around $328/mth).
This had a consequential effect of reducing residual heat in the room, nutrient and water tanks, with profound effects reducing mould and fungus problems.

These figures just blow me away. The total "light ON" period of 500hrs to get a harvest is amazing. That is only 2/3rds of the time and 50% of power that a regular CO2 equipped growing operation is using. In just 1/2 of the time at 1/3rd of the power, a better harvest than ever achieved with a 16week method.
For the flower seeds he is cropping, he has hit a crop rotation and growing efficiency that would make most people's eyes water.
Good luck to him.

Hope that this is of interest to all in Home Growing Heaven

2 Can · #2 02-06-2009, 05:11 AM

I've not tried this method but it sounds really interesting. The only downside appears to be that 18 hour timers seem few and far between - you either need to get a mega expensive CO2 controller or an Australian company makes them for about £100 each.

Any other sources for timers would be great to hear about.

eza82 · #3 02-06-2009, 05:12 AM

Find me a Dutch grow house incorparating these tech`s....... or a commercial operation with this cycle on vegtables ???? Ive looked you wont....... Sounds great in theory........

eza82 · #4 02-06-2009, 05:19 AM

plants need the period of 24hrs because of hormone production...... over thousands of yrs plants have learnt to grow over 24hrs.... plants cells dont stop dividing nor hormones flowing and production of some hormones are done in the late hrs of the `OFF` period.
So i guess this is my justification in theory for why it would not work....
But please try, We hear talk of it all the time but no one has reported back on a result!
Good luck......

2 Can · #5 02-06-2009, 05:30 AM

I know I know... but it's got me hooked & wanting to try it out. I'm a sucker for this sort of snake oil... LOL

I was thinking maybe running 2 seperate identical DWC buckets, using same cuttings in each one and see what happens. It should be quickly evident if there's anything in this 18 hour theory...

Unfortunately it's very hard to find the timers which is probably why so few people have attempted it. I can't find any for sale apart from the Australian company

eza82 · #6 02-06-2009, 05:34 AM

Manual - would be a nightmare..... but do`able if you think your going to save that much.... just do it for a month see what happens - set an alarm on your phone or watch.....

eza82 · #7 02-06-2009, 05:35 AM

Just use a 24 hr digital just do your MATH.....

eza82 · #8 02-06-2009, 05:38 AM

Ive got one that has 90 programable slots for on off periods over 7 days...

budder · #9 02-11-2009, 08:24 PM

Is it true that roots only grow at night, or in dark? Thanks

eza82 · #10 02-11-2009, 08:40 PM

Quote:

Originally Posted by budder

Is it true that roots only grow at night, or in dark? Thanks

Wives tail.......... cell division happens 24/7 in plants which is growth.... in both directions!......

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