Throw out that thermometer...?

Can you all say your thermometers only read the air temperatures or are they influenced by external heat, light and radiation?

When i managed to set this thermo dude in the right housing and in the right position in my tent i realised upto that point i was not accurately reading the correct air temperature.

For example a weather station that reads air temperature cannot be influenced by any external heat lifht or radiation. It isshaded, ventilated, raisedof the ground and kept free from any light and radiation, i dont think we go anywhere close trying to produce accurate air temperatures yet we all go of what our thermometer says.

So ditch the thermometer or construct a small weather box for my thermometer and place in the most dim shaded part of my tent above and away from the light as in the principle used to get this kind of accuracy?

A lot of guys have them too close under the light and get readings much higher than the actual air temp. I have my themometer/hydrometer with the thermostat for the heater and a remote Therm/Hydrometer on an open shelf about 4 feet from the light on an inside wall right in a good air flow. Should be getting reliable readings there.

The remote is nice and I have the LED display right above my monitor here in the mancave. A glance up lets me know how things are. If the light didn't come on it will be too cool and if it didn't go off it will be too warm then I know to go check things out. I have a remote camera too but it only gets one channel and the same show is always on so I don't use it much.

I keep the remote sensor for outdoors in the carport out of the sun and weather sitting on a file cabinet a few feet from the wall so it won't be influenced by any heat from the house. The display is in the kitchen. Lowest recorded temp is -37.0C/-34.6F and highest 42.6C/105F Quite a range of temps way up here in the north. Have to use the lithium AA batteries outside as Duracells cut out around -25C. Same batteries have been in it since I got it at least 7 years ago.

Hanging above the light line with good air circulation should be enough.

Its one of those subjects, i'm always amazed at how little proper temp reading is talked about.

See someone every day raving on about high temps with a thermometer directly under a light.

I was guilty too at one point but you learn the science and realize those readings were not of the actual air temps. I dont even feel that we can read accurate canopy temps without pimping out thermometers out not to read any other heat sources.

My tent would appear to be FUCKING HOT AS HELL under the light, above it is reasonably cool and it is there i believe the real air temperature can be close to accurately read.

ok this is all well and good... but you're trying to say the sun (or our lights as we are mimicking the sun) should not be a factor in how we record our temps and how our plants are reacting to that temp?

Kingrow1 said:

Can you all say your thermometers only read the air temperatures or are they influenced by external heat, light and radiation?

When i managed to set this thermo dude in the right housing and in the right position in my tent i realised upto that point i was not accurately reading the correct air temperature.

For example a weather station that reads air temperature cannot be influenced by any external heat lifht or radiation. It isshaded, ventilated, raisedof the ground and kept free from any light and radiation, i dont think we go anywhere close trying to produce accurate air temperatures yet we all go of what our thermometer says.

So ditch the thermometer or construct a small weather box for my thermometer and place in the most dim shaded part of my tent above and away from the light as in the principle used to get this kind of accuracy?

Click to expand...

great observation

meangreengrowinmachine said:

ok this is all well and good... but you're trying to say the sun (or our lights as we are mimicking the sun) should not be a factor in how we record our temps and how our plants are reacting to that temp?

Click to expand...

was thinking the same even if the air temp is cool say in a larger room with only one light an ac and fan blowing over the canopy the ir can still fry your plants


Maby we should start using 2 thermometers one at canopy level under a light and another shielded a few feet away then you would know the air temp and how bad the ir is heating the canopy to much.

Dynamo626 said:

great observation

was thinking the same even if the air temp is cool say in a larger room with only one light an ac and fan blowing over the canopy the ir can still fry your plants


Maby we should start using 2 thermometers one at canopy level under a light and another shielded a few feet away then you would know the air temp and how bad the ir is heating the canopy to much.

Click to expand...

I have thought about doing this before actually but was not really sure the use in my case as I am pretty small time and temps are usually reasonable

Heat rises. Placing the thermometer above the light is not going to provide an accurate measure of air temp near the plants.

A shaded spot in the same area as the plants is where the thermometer should be located. The base of the plant is a logical area, but the thermometer should not be directly on the soil. Use an insulating layer, such as a small piece of closed-cell foam, to get the thermometer off the soil. If your plant is too sparse to create complete shade, make a tinfoil umbrella for the thermometer (tinfoil, toothpicks, tape). Ensure good air circulation in the plants' space. The ambient temperature reading will be accurate.

For measuring canopy temperature (which is something entirely different) I use an infrared thermometer.

meangreengrowinmachine said:

ok this is all well and good... but you're trying to say the sun (or our lights as we are mimicking the sun) should not be a factor in how we record our temps and how our plants are reacting to that temp?

Click to expand...

Yes completely just like in all scientific disciplines and weather recording stations.

You must omit all other heat sources so the air can be measured accurately.

cogitech said:

Heat rises. Placing the thermometer above the light is not going to provide an accurate measure of air temp near the plants.

A shaded spot in the same area as the plants is where the thermometer should be located. The base of the plant is a logical area, but the thermometer should not be directly on the soil. Use an insulating layer, such as a small piece of closed-cell foam, to get the thermometer off the soil. If your plant is too sparse to create complete shade, make a tinfoil umbrella for the thermometer (tinfoil, toothpicks, tape). Ensure good air circulation in the plants' space. The ambient temperature reading will be accurate.

For measuring canopy temperature (which is something entirely different) I use an infrared thermometer.

Click to expand...

heat rises but that is negligible in my tent when i switch on an inline and generate 400cfm of negative pressure in a small room.

Our lights do not influence air temps much i feel.

I always assumed the recommended temps for growing were supposed to be actual leaf temperatures, as in the surface temp. I don't have a laser thermometer so I can't measure it that way, but that's how I understood it.

As for air temps, I don't have a thermometer in my flowering tent anymore, and the one in my veg cab I hardly ever look at, it's there somewhere though lol.
I watch the plants now to see how they're responding.

Kingrow1 said:

heat rises but that is negligible in my tent when i switch on an inline and generate 400cfm of negative pressure in a small room.

Our lights do not influence air temps much i feel.

Click to expand...

I do not think that is accurate at all. So what in your mind makes the drastic change from daylight to night time temps if not the light? Be it from the sun or a large light acting as the sun?

cogitech said:

Heat rises. Placing the thermometer above the light is not going to provide an accurate measure of air temp near the plants.

A shaded spot in the same area as the plants is where the thermometer should be located. The base of the plant is a logical area, but the thermometer should not be directly on the soil. Use an insulating layer, such as a small piece of closed-cell foam, to get the thermometer off the soil. If your plant is too sparse to create complete shade, make a tinfoil umbrella for the thermometer (tinfoil, toothpicks, tape). Ensure good air circulation in the plants' space. The ambient temperature reading will be accurate.

For measuring canopy temperature (which is something entirely different) I use an infrared thermometer.

Click to expand...

Technically not, hot air rises in a convection current, heat dissipates evenly throughout it's environment....sorry I had too

Kingrow1 said:

heat rises but that is negligible in my tent when i switch on an inline and generate 400cfm of negative pressure in a small room.

Our lights do not influence air temps much i feel.

Click to expand...

The heat in the air will most likely come from the light source, wether that is directly or radiated heat from the light housing, reflector, bulb etc.

Kingrow1 said:

heat rises but that is negligible in my tent when i switch on an inline and generate 400cfm of negative pressure in a small room.

Our lights do not influence air temps much i feel.

Click to expand...

I have a similar air flow setup, and my infrared thermometer tells a different story.

The heat goes somewhere before it gets exhausted. It goes up.

If the lights did not influence air temps, you wouldn't need any ventilation.

SonsOfAvery said:

Technically not, hot air rises in a convection current, heat dissipates evenly throughout it's environment....sorry I had too

Click to expand...

No worries. You're correct, of course. However, the hot air rising in the convection current collects in the top half of the tent (above the light) and meanwhile the exhaust fan is drawing that hot air up and out. The hottest air will always be at the top of the tent due to both the convection current and the negative draw of the exhaust fan.

This assumes, of course, that there is no auxiliary fan blowing hot air down, or blowing cooler air up. Vertical air circulation should be avoided, unless you need to mix warm air down to the plant area.

Yeh, sorry I just had to lol. Agreed the hottest place in my tent is at the top, I don't need a thermometer to tell that, just stick my head in and you can feel the difference from top to bottom, but I do have an in-line fan at the bottom bringing air in.

Kingrow1 said:

Can you all say your thermometers only read the air temperatures or are they influenced by external heat, light and radiation?

When i managed to set this thermo dude in the right housing and in the right position in my tent i realised upto that point i was not accurately reading the correct air temperature.

For example a weather station that reads air temperature cannot be influenced by any external heat lifht or radiation. It isshaded, ventilated, raisedof the ground and kept free from any light and radiation, i dont think we go anywhere close trying to produce accurate air temperatures yet we all go of what our thermometer says.

So ditch the thermometer or construct a small weather box for my thermometer and place in the most dim shaded part of my tent above and away from the light as in the principle used to get this kind of accuracy?

Click to expand...

Straight away I see an issue as any heat from the light will, thanks to convection, start to head "down" from the top of the tent there so will not be an accurate measurement of what is happening at plant level.

So where is the ideal height to measure temp at?

Kingrow1 said:

heat rises but that is negligible in my tent when i switch on an inline and generate 400cfm of negative pressure in a small room.

Our lights do not influence air temps much i feel.

Click to expand...

Then it can be argued that the temperature will be influenced by the ventilation, or give a false reading thanks to being in "dead air".

Fubard said:

So where is the ideal height to measure temp at?

Click to expand...

Soil level, however not directly on the soil, in the shade (either plant shade or shade created specifically for the thermometer).