Maximum temperature during specific conditions

I red maximum temperature should not exceed 31C (87.8F).
My flowers are not in small box, but in dedicated big room.

Right now if I place thermometer on my pots I have arround 31C (87.8F) under 600W lamp.
But fan is blowing cooler air 25C (77F) from distance thanks to room size.


Do you think that under these conditions it's more acceptable to have higher temp under the lamp?
Should I still place my light higher and lower the temp under the light?

How are the plants responding?
Do they look healthy and vigorous?
Or are they drooping and tired looking?

They are looking healthy, but their leaves are not in position for catching maximum of light.
I red too high temperature is slowing grow.

My dilemma is: more light or less temperature

CyberGanja said:

They are looking healthy, but their leaves are not in position for catching maximum of light.
I red too high temperature is slowing grow.

My dilemma is: more light or less temperature

Click to expand...

The answer you're looking for is in your last sentence. You want to achieve more light at a lower temp.
600 watts should be perfect for light but how many plants do you have under this light? How far is the light from your canopy?

Temp's during lights on, shouldn't be over 82 F at canopy level. Raise the light 6 inches and check the temp an hour later. If it's still above 82 F at canopy level, raise the light another 2 inches, repeat until temp is 82 F or under. Then you'll see your plants really take off. If kept in their current conditions, the heat stress alone, will reduce overall growth and eventually your yield. So really it's not a dilema, more a matter of necessary adjustments.

I'm planning 9 big pots.
Distance is little bit more than one meter (39.3701 inches)

Here are some photos, sorry for poor quality I have only nexus7, 1 MPX camera




Plants have different age. Biggest sit 11 days under this light and I repoted them today.

OneStonedPony said:

Temp's during lights on, shouldn't be over 82 F at canopy level. Raise the light 6 inches and check the temp an hour later. If it's still above 82 F at canopy level, raise the light another 2 inches, repeat until temp is 82 F or under. Then you'll see your plants really take off. If kept in their current conditions, the heat stress alone, will reduce overall growth and eventually your yield. So really it's not a dilema, more a matter of necessary adjustments.

Click to expand...

To expand on that note.
At temps over 80F your plants will begin to slow in growth until you reach about 90F and then they will begin to go "dormant".
Plants that are under C02 use can tolerate higher temps to around 84F - 86F with minimal slowdown.
The use of Silica can help out heat tolerance to a point. But don't count on that helping much!

Raising lights can cause stretching, depending on the distance from the canopy.
So then, what is the distance of the light to the canopy? If it's an air cooled hood, measure from the glass to the canopy. If a "wing" style is used, measure from the imaginary line from one side of the wing to the other.

OneStonedPony said:

Temp's during lights on, shouldn't be over 82 F at canopy level. Raise the light 6 inches and check the temp an hour later. If it's still above 82 F at canopy level, raise the light another 2 inches, repeat until temp is 82 F or under. Then you'll see your plants really take off. If kept in their current conditions, the heat stress alone, will reduce overall growth and eventually your yield. So really it's not a dilema, more a matter of necessary adjustments.

Click to expand...

OK. I will do it

OneStonedPony said:

Temp's during lights on, shouldn't be over 82 F at canopy level. Raise the light 6 inches and check the temp an hour later. If it's still above 82 F at canopy level, raise the light another 2 inches, repeat until temp is 82 F or under. Then you'll see your plants really take off. If kept in their current conditions, the heat stress alone, will reduce overall growth and eventually your yield. So really it's not a dilema, more a matter of necessary adjustments.

Click to expand...

To expand on that note.
At temps over 80F your plants will begin to slow in growth until you reach about 90F and then they will begin to go "dormant".
Plants that are under C02 use can tolerate higher temps to around 84F - 86F with minimal slowdown.
The use of Silica can help out heat tolerance to a point. But don't count on that helping much!

Raising lights can cause stretching, depending on the distance from the canopy.
So then, what is the distance of the light to the canopy? If it's an air cooled hood, measure from the glass to the canopy. If a "wing" style is used, measure from the imaginary line from one side of the wing to the other.

You answered before I could post this one.
I see from your pic's that I would focus the closer fan on the light to reduce the temp. If the room temp gets to 80F then you should exhaust heat out and in vent low to the floor for cooler intake air. Lower your light 25% and check temps again.

Dr. Who said:

You answered before I could post this one.
I see from your pic's that I would focus the closer fan on the light to reduce the temp. If the room temp gets to 80F then you should exhaust heat out and in vent low to the floor for cooler intake air. Lower your light 25% and check temps again.

Click to expand...

Unfortunately for me, only more distant FAN is working.
Closer died previous grow and i'm using it only as a stand for webcam (i'm taking pictures each 10 minutes for nice final video of grow)

So I'm going to raise the light as suggested.
Another option would be to open windows, because its winter here
But I'm living in same room too, so it's not a solution.

Well thanks for suggestions. In future I'm planning to buy closed hood with hole for air suction of heat, but now I have to work with what I have.

Oh, I'm using analog thermomether and I realized it shows different values depending on its position (horizontal X vertical)

Vertical position shows temp 26.5C(79.7F)
Horizontal position shows 31C (87.8F)

I will try to find another one to be sure.

BTW you mentioned CO2 -

My room is about 140 square meters (~1506.95 sq foot)
I'm living in it almost 24/7.

I'm producing some CO2 for sure, but is it enough to have positive effect on plants? I'm really here all the time. working here + sleeping.

How do you get a 79.7 reading analog?

One thing extra to take in consideration....
The Temp and RH in the area right between the lights and plant top cola...
This area, Runs +7 f degrees hotter and -7 points lower in RH...
So keep this in mind...

That's a pretty big room. Your room (depending on the layout) is approx 39ft x 39ft (1521 sqft). Perhaps you should invest in a grow tent to better control the garden environment.
Or invest in another fan to blow across your light and turn your furnace thermostat down. Use the thermal energy generated by the light to heat your room.
You can get an accurate temp meter at just about any hardware store, need to start there.
Are you on a really tight budget?

Sand4x105 said:

How do you get a 79.7 reading analog?

Click to expand...

My thermomether uses Celsius system I just tried to convert it to Fahrenheit for USA people.

Sand4x105 said:

One thing extra to take in consideration....
The Temp and RH in the area right between the lights and plant top cola...
This area, Runs +7 f degrees hotter and -7 points lower in RH...
So keep this in mind...

Click to expand...

Yes, plants are small now, vertically aligned thermometer is right now approximately at the same level as top colla. When plants get bigger i'm going to attach thermometer on string.

jazlm said:

That's a pretty big room. Your room (depending on the layout) is approx 39ft x 39ft (1521 sqft). Perhaps you should invest in a grow tent to better control the garden environment.
Or invest in another fan to blow across your light and turn your furnace thermostat down. Use the thermal energy generated by the light to heat your room.
You can get an accurate temp meter at just about any hardware store, need to start there.
Are you on a really tight budget?

Click to expand...

Yes, that 600W HPS is considerably heating my room, during winter its nice.
During my previous grow I actually had two fans working and used one to blow away heat from tube, but it appeared to be much less effective than I thought.

I'm plannning to buy something like this -> (SPUDNIK Air cooled reflector) hoping this will solve my troubles with heat.
I don't like grow tents, they are too small (biggest ones are nice, but too expensive). And i'm trying to grow big trees.