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Light Contamination In 12hr Dark


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i've heard so many different stories.

from "any light at all, anytime, during 12hr lights-out and they're totally f*****d"

to "no probs, an occasional flash of light is ok"

and even " you can go in there with a torch in an emergency" this from a grow shop owner.

so please!! what's the royal scam?

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The effect of allowing even small amounts of light into the plants whilst in their flowering period will be a direct reduction in flowering hormone response. In other words, smaller flowers overall, or fewer.


The flowering response in a short-day flowering plant is determined by the length and intensity of the dark period, not the light. The effects of reducing the length of the dark period to below 10 or less hours doesn't allow the plant to build up a sufficient amount of flowering signal hormones, thus it remains in a vegetative phase. Once you cross the critical level for the plants, (and this will vary slightly with each strain, and individual to some degree, but it's usually around the 12/12 mark, sometimes less, sometimes more.) the signal is given to flower.


Interrupting the dark cycle of flowering MJ plants will essentially reduce your yeild. Depending on how well you light proof it, and how much other light is present during the otherwise pure dark period, it could be a small drop, or a fairly large one in a badly set up growroom.


It won't be fatal, but if you're trying to flower them and you have massive gaps in the walls where large volumes of light can contaminate the dark period, then you might not even get to flowering...


So in a growroom which is emulating the natural period of dark and light of the seasons, light during the dark phase can both reduce yeild, and reduce flowering response. :P


Hope that gobbledegook helped. :D

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The effect of allowing even small amounts of light into the plants whilst in their flowering period will be a direct reduction in flowering hormone response.



thanks, that is (less the science) what i believed to be true.

i am talking about a very small amount of light, maybe a dehumidifier that has a cover on it to cover small amount of light coming from the control panel, and the cover slips for a second or two.

or, where the air/con exhaust-pipe runs outside and a small amount of diffused light is visable, so little that you really have to look hard to see it. a slight, diffused, barely dissernable glow inside the pipe just for an hour or two.

if apart from these rare incidents its totally light-tight what would be the effect?

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The ideal thing would be to keep them in complete continuous darkness in the dark period but as we all know, in an outdoor grow plants are not always in complete darkness for instance when there is a full moon or an electrical storm.

This may have a small effect on their finishing times but they will finish nevertheless. :D

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I am currently working on a moon simulator for my friends grow room, the idea is to attach an adjustable light disc to a light rail that will simulate the light from the moon.

What is your thoughts. I saw one being used on television in antarctica hydroponic installation.Apparently NASA uses them too for its space garden program. But Im having problems finding any information about it .




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good idea buddy, another great idea if you HAVE to go into your 12 hour room when lights are off, is to wear all black clothes and a ski mask/balaclava.This will minimise light refraction as well and should keep flower impedament to a minimum..If you dont have a ski mask you could put boot polish on your face and a hair net if your wife has one lying around.




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If you need to potter about in the grow room during the dark period you can install a dark room safe light (used in photography).

i don't think so. thats the wrong sort of light, red not green. this is deliberate deception.


no, the only thing thats works is no light at all.

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