Humidity higher when lights off?

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Laxstar13

Member
Im in my last week of flowering and for the past 2 days when i check my plants at lights on the humidity is at like 70%.
Its around 50% when the lights are on.
I dont get it because all the fans are still on only thing that changes is the light is off
There is a space heater in there to keep temps up during lights off?? dont know if that could do it.
Thanks guys
 
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thalboy

Active Member
During the night cycle the plants will exhale humidity. You need to watch that high humidity because you can end up with bud mold. Get a dehumidifier if necessary or some dehumidifying crystals.

When you say "around 50%" is that usually under or over 50%? That's even a little high for my taste. I'm at 40% now and happy with that.
 
OZUT

OZUT

Active Member
thalboy said:
During the night cycle the plants will exhale humidity. You need to watch that high humidity because you can end up with bud mold. Get a dehumidifier if necessary or some dehumidifying crystals.

When you say "around 50%" is that usually under or over 50%? That's even a little high for my taste. I'm at 40% now and happy with that.
Click to expand...

Actually it's got nothing to do with plants exhaling humidity...When your lights go off, the room cools and the humidity in the room sets on your leaves....when your lights go on, they dries the room...That's why it's lower during lights on....

The bigger the temp difference between lights on an off, the bigger your humidity will spike without a dehumidifier....it's the main cause of powdery mildew...Get yourself a dehumidifier and set it on a timer to go on when the lights go off....Depending on the size of your room, it gives off a good amount of heat, which is also kind of in your favor because it'll keep the temperature difference between day and night not as extreme...especially in the winter....Your fans don't control humidiy
 
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gobbly

Well-Known Member
this should be obvious... When your lights are on they are creating heat, which hastens evaporation. To test this, take two glasses of water outside, dump one on the cement in the shade, the other in the sun, see which dries up faster :)
 
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thalboy

Active Member
Plants transpire 90% of the moisture they take up. When you are flowering your plants will have more surface area from which they transpire which causes them to drink more water, which leads to a circular effect. At the end of flowering your plants are transpiring a lot more moisture then they were at the beginning. I had heard that they transpire more during the dark period than the light, although I can't find a source for that right now and I may have heard incorrectly.
 
makinthemagic

makinthemagic

Well-Known Member
yes humidity will rise. there will be the same amount of moisture in the air and the temperature will drop. its been awhile since chemistry but i know that makes the humidity higher.
 
OZUT

OZUT

Active Member
Cold air cannot hold as much water vapor as warm air. As temperature drops relative humidity rises. Absolute humidity remains constant until the dewpoint temperature is reached, then decreases with temperature as water precipitates out of the air. Below the dewpoint temperature relative humidity remains constant at 100%
 
L

Laxstar13

Member
I did just lower the night time temp
So im guessing this is what caused this and why i didnt have a problem befor
ILl try putting it back up and see if that helps
Thanks you guys are awsome
Also where would i buy dehumidifing crystals?? anyone know?
 
OZUT

OZUT

Active Member
Don't waste time with the crystals bro, it's not going to do anything....They're good for when you're drying your buds but anything bigger than a 4x4x4 area will need more than crystals...Jump on craigslist and get a small used unit
 
L

Laxstar13

Member
well my grow room is not that big and cant fit a dehumidifer in it so i was thinking crystals might be an option my room is only 3x5x4
 
OZUT

OZUT

Active Member
Laxstar13 said:
well my grow room is not that big and cant fit a dehumidifer in it so i was thinking crystals might be an option my room is only 3x5x4
Click to expand...

yeah that's a little different...Still wouldn't go with the crystals...won't go more than a week or so...Go to Home Depot and they have really small ones that collect the humidity and you can empty it out once a day...They cost like $20 but will last you much longer than crystals
 
L

Laxstar13

Member
I cant seem to find anything other that the crystals, cant find the type of thing thats in the link from stratkilla911
been to walmart, homedepot, sears, canadian tire
but that thing works with silica crystals so basicly wouldnt it do about the same?
 
OZUT

OZUT

Active Member
Sorry bro, not sure about Canada....


It just hit me, go to a store or a department for infants or toddlers...Down here, almost every single baby store carries small dehumidifiers for baby rooms...They're actually the best size for what you're looking for
 
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