Dim LEDs near harvest ?

Hi all.
In the interest of saving more power ( my bill just came and its 3.7k). Is there any experience in here when it's ok to dim the lights without any yield loss? I mean this is a major advantage for us LED users to be able to dim up to 1/10th.

From my own experience, I usually dim the LEDs the day I start chopping my first plant. No idea on the effects though.

Also, another thing that I'm very interested in is late in flower, when the buds are falling down. Are the bud getting heavier? OR are the stems getting weaker? Knowing this may also determine our decision if to dim.

All experiences, theories and ideas are welcome.

i usually run full tilt until at least the tops are taken

goofy81 said:

Also, another thing that I'm very interested in is late in flower, when the buds are falling down. Are the bud getting heavier? OR are the stems getting weaker? Knowing this may also determine our decision if to dim.

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many strains put a lot of weight on in the last week. i dont think stems get any weaker, if anything more woody and rigid with age

Buds are getting heavier.

IME both LED and HPS it is advisable to dim 25% to encourage ripening as would be the case in a natural environment with light weakening and temps dropping later in the season.

10-14 days before harvest on a 70 day strain or 10-7 days on a 56-60 day one.

Full power to harvest for optimum yield, then a 48-hour dark period before chopping to marginally increase THC. In simple terms, THC glands are produced during the dark period and broken down into CBD by UV light. The last couple of days in the dark stimulates gland production whilst reducing UV break-down.

In practice, the results are noticeable.

^what about in a garden that lacks uv to begin with

Prawn Connery said:

Full power to harvest for optimum yield, then a 48-hour dark period before chopping to marginally increase THC. In simple terms, THC glands are produced during the dark period and broken down into CBD by UV light. The last couple of days in the dark stimulates gland production whilst reducing UV break-down.

In practice, the results are noticeable.

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Its well established that THC is not a precursor of CBD.

nfhiggs said:

Its well established that THC is not a precursor of CBD.

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It's CBN after THC breaks down I'm pretty sure. Some of the older literature references CBD. It's a some what common mistake.

Yep, sorry this ^

CobKits said:

^what about in a garden that lacks uv to begin with

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I wouldn't know, as I've never grown without it. I think the evidence is irrefutable in favour of the direct correlation between UVB and cannabinoid production - UV levels are elevated in the higher and equatorial regions where indicas and sativas evolved - so think of it as sunscreen for plants. And trichomes are still produced during the dark period. I stand to be corrected if there's evidence to the contrary.

ive seen studies suggesting it but i wouldnt call it irrefutable, as in every grower will see a difference with every strain

CobKits said:

many strains put a lot of weight on in the last week.

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Do they though? It's my experience that at some point they stop packing on more weight and then you're just waiting for the ripening. That's usually the last week (up to two weeks for a longer flowering strain).

But then I guess it also depends on what you feel is when he trichomes are done. If you harvest on clear or wait till amber can give a large spread in flowering weeks. When harvesting on clear trichomes, the buds might still pack on weight in the last week.

Prawn Connery said:

I think the evidence is irrefutable in favour of the direct correlation between UVB and cannabinoid production

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there's lots of folks growing potent herb with just white leds, no added UV...

Prawn Connery said:

And trichomes are still produced during the dark period. I stand to be corrected if there's evidence to the contrary.

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autoflowering strains don't require a dark period but can produce copious trichomes nonetheless...

Prawn Connery said:

I wouldn't know, as I've never grown without it. I think the evidence is irrefutable in favour of the direct correlation between UVB and cannabinoid production - UV levels are elevated in the higher and equatorial regions where indicas and sativas evolved - so think of it as sunscreen for plants. And trichomes are still produced during the dark period. I stand to be corrected if there's evidence to the contrary.

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UV is usually not worth the trouble though, in my opinion. The lights don't last long, due to UVB being so destructive, and need to be very close due to UVB dropping off rapidly from the source. Since nobody seems to gripe about 23 % THC weed, doubt it's worth it. You just need a good strain/pheno and adequate light levels. I think a lot of people will be causing injury to themselves trying to get a few percentage points more THC with UVB light.

Guys, every time you step outside you step into UV light. It's called the sun. Cannabis plants have evolved under it, and there is absolutely no doubt they evolved in the highland areas of Central Asia and equatorial regions around the world where UV concentrations are higher. I've been to these places and seen many land-race strains in their natural environment. There are plenty of scientific studies that, at the very least, claim cannabinoids evolved in direct response to UV oxidation (among other environmental factors), as THC is proven to have high UVB absorbtion properties that protect the plant and seed casing.

Auto-flowers were derived from Ruderalis, which is naturally found in east Asia, and not know for its potency in land-race form. It was only through crossing indica and sativa strains with selective breeding that their potency was improved. I've never grown an auto-flower - I don't, frankly, see the point - but what they offer in potency, they owe to pure genetics. As we all know (or at least should), genetics get you only so far - to reach full potential, one must have the right environment.

Don't get me wrong - you can grow potent weed with smaller amounts of UV. But is it as potent (in terms of cannabinoid production) as it could otherwise be? You can only answer that question for yourself when you have harvested the same strain, under the same environmental conditions with and without a dark period as empirical evidence. I have - over many years of growing - and anecdotally, I believe it makes a difference. Your mileage may vary, but honestly, it only takes 48 hours of dark to convince yourself or otherewise.

Those saying that white LED light contains no UV . . . that's simply not true. All LEDs emit UV, even if it is just a small amount.

Prawn Connery said:

that's simply not true. All LEDs emit UV

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Any spectrum graph I've ever seen for white leds drops off to 0 at around 410nm

I wouldn't dim late either. Their is no measurable uv in our popular led Kelvin choices.

48 hrs darkness had no noticeable effects to me vs just continuing flower cycle in my experience.

I personally have never noticed any improvement in quality or other benefits from an extended dark period before harvest (I've tried it many times with different strains over the last 13 years of growing) but to each his own...

I have had success with dimming and reducing daylight hours during the final 1-2 weeks to help certain strains finish ripening though (plus lowering temps & rh and watering with cooler water)..

If I use a 48 hr dark period, I get bud rot every time.. Now I chop after the normal 12 hr dark period..

I'd look at the plants too though. If you see the leaves drying out then I do think it would have been better to dim the lights before.