What happenes when cannabis gets too much light?

[Nanook]

Maybe because of the QB and spread it stops the old hotspots we used to get with hps?

[Captain Beefheart]

That's what I am trying to discuss here.
Is that 1000 mh lamp going to produce too much energy right under the lamp and don't spread the light properly all over your 10 x 10 room OR you sill be able to use 4x200w LED panels in total of 800w which are producing the right light for the plants to grow healthy and save some pennies in your pocket?

its all trial and error bulls bach im afraid butty,its your gaff so we soon see wont we

[kbag]

Hmm i see a need for a gadget?

[Nanook]

hahaha KB, my phone only runs to 90000 and maxes out :( I did look at gadgets but they are expensive and tbh I have spent a fortune lately - theres only so much the wife will allow hahaha

[Captain Beefheart]

who needs gadgets mun...........i aint even got a thermometer

[kbag]

A high light plant such as Cannabis needs a minimum of 22 mols/m2/day of photons to as high as 65 mols/m2/day which is the range of optimal growth. Yes if you don't have that much light, cannabis will still grow, but you will typically see lower yields, less dense buds, lower THC percentages because the plant isn't operating at its best.



Converting DLI to PPFD
Now how do we get from DLI Mol/m2/day to PPFD or micromoles/m2/second.

The formula to convert this would be:
You would use this formula...

PPFD x 0.0864 = DLI
OR
DLI / 0.0864 = PPFD

So lets look at cannabis, knowing that cannabis needs at least (Minimum for optimal growth) 22mol/m2/day DLI at minimum for optimal photosynthesis lets break it down.

22 / 0.0864 = 254.6 micromoles/m2/s-1 (PPFD)

This is the amount of photons you need every second, averaged over 1 square meter, for the whole 24 hours if usuing a 24/0 daylight schedule (no dark period).

So what happens if you are using a 18/6 veg period or a 12/12 flowering light schedule... simple...

If using a 12/12 flowering schedule, you are only using 12 hours of the 24 hours of the day, which means you would take the 254.6 Micromoles/m2/s-1 and multiply it by 2, since you are reducing the amount of daylight by 1/2 (12 hours), then each hour of the daylight period you need double the amount of photons... so in this example you would need 509.25 micromoles/m2/second.

If using a 18/6 schedule, you are using 3/4 of the amount of daylight with 18 hours on, 6 hours off, therefore you would multiply the 24hr PPFD by 1.5 because you are using only 3/4 of the day, or 1 1/2 times the 12 hour requirement. In this example a DLI of 22, under a 18/6 schedule would amount to 381.5 micromoles/m2/second.


So for cannabis, bottom threshold for optimal growth and photosynthesis is a DLI of DLI of 22 would be:
****Going lower than these numbers will still grow cannabis, however yields, bud density, potency and THC percentage may suffer.
24/0 schedule: 254.6 micromoles/m2/s-1
18/6 schedule: 381.5 micromoles/m2/s-1
12/12 schedule: 509.25 micromoles/m2/s-1



For Cannabis, the Top threshold for optimal growth and photosynthesis is a DLI of 65 moles per day.
***extremely important notice, only go up to these amounts if you are using supplemental CO2, do not go this high if you are not using supplemental CO2 as you will actually slow down photosynthesis and waste energy.

24/0 schedule: 752.31 micromoles/m2/s-1
18/6 schedule: 1128.465 micromoles/m2/s-1
12/12 schedule: 1504.6 micromoles/m2/s-1


The generally accepted guidelines for artificial light PPFD in flowering are this:
in a 12/12

PPFD of at least 510 micromoles/m2/s-1 for the low end of optimal intensity
PPFD of at least 800-1100 micromoles/m2/s-1 for perfect optimal lighting without additional CO2.
PPFD of at least 800-1500 micromoles/m2/s-1 for perfect optimal lighting WITH additional CO2.

This is not my post and was copy and pasted

[Bulls]

I've personally experienced "What happens when cannabis gets too much light?" recently.
I've had my Invisible Sun on full power, thinking like similar to other LEDs and HPS I will need at least 250w to be able to veg 6 plants in 10L pots in a 0.5 x 1.8 x 1.7 Area.
Well I was waaay wrong! On 250w the plants started to turn yellow and stopped growing.
Once I lowered the light to 90 w they are flying! As I mentioned it elsewhere I am simply amazed how 90w are covering that area and giving enough light to 6 plants to veg properly.

Here are comparison photos: Plants Under 250 w






Here are the plants under 90 w

[Nanook]

Good post bulls :)

[Tom123]

Good shout. Nice to know.


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[Unknown User]

Since I'm probably the only one left here that gets 40° + temps id say high UV and leaving the fan leaves on makes a real difference. As I'm finding this season its all about changes in temps through light hours.
The temps and UV need to increase slowly to peak for a few hours a day then decline to around 25° in dark hours with good airflow as the cooling starts.

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