Measuring leaf surface temp

My grow room is to a point now that i can very accurately control all variables. Humidity, temp, reservoir temp (dwc), co2. This means i have the ability to really nail a perfect vpd at all times but to do so properly i need accurate leaf surface temp. I have a cheap infrared gun but i dont know if it accurately reads a leaf. It does seem to be at least consistent, but no idea if its accurate. My veg plants are under a 1000watt mh, 83F ambient at canopy, 65RH (50 at night), 1500ppm co2, and my IR gun is telling me 78F at the leaf. Should i trust my cheap gun or do i need to get a horticulture specific IR gun if i want accurate leaf surface temp? Any reccomendations that dont cost hundreds?

DWCgrower406 said:

My grow room is to a point now that i can very accurately control all variables. Humidity, temp, reservoir temp (dwc), co2. This means i have the ability to really nail a perfect vpd at all times but to do so properly i need accurate leaf surface temp. I have a cheap infrared gun but i dont know if it accurately reads a leaf. It does seem to be at least consistent, but no idea if its accurate. My veg plants are under a 1000watt mh, 83F ambient at canopy, 65RH (50 at night), 1500ppm co2, and my IR gun is telling me 78F at the leaf. Should i trust my cheap gun or do i need to get a horticulture specific IR gun if i want accurate leaf surface temp? Any reccomendations that dont cost hundreds?

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Read your plants
If you are running at 83f which is borderline as far as a HID lamp supplemented with CO2
and plants are happy then I wouldn't concern myself with leaf temps as much as canopy

I don't even know how you could change that given your conditions other than air circulation which I assume you have covered ?

You don't need an expensive one. Leaf temp is usually a few degrees cooler than room temp so it sounds good to me

Herb & Suds said:

Read your plants
If you are running at 83f which is borderline as far as a HID lamp supplemented with CO2
and plants are happy then I wouldn't concern myself with leaf temps as much as canopy

I don't even know how you could change that given your conditions other than air circulation which I assume you have covered ?

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My conditions are what i have set them to. I have the ability to set them to whatever i want, but without accurately knowing leaf temp, i dont know for sure exactly what my other conditions should be set to. Theres a few ways leaf temp can be changed. Lowering RH increases transpiration, increasing plant cooling, leaf temp drops, raising lights drops it, lowering ambient temp drops it. Small change in leaf temp has a pretty large impact on vpd.
I figured if i have the equipment and capability to control these variables for optimal vpd, then why not put the effort into doing it. Mostly im just curious if my temp gun should be trusted or not. If my leaf temp is actually 2 or 3 degrees off where my gun is telling me, my plants are capable of doing better. They are happy and im sure harvest will be good, but why not optimize and do better if possible?

I was going to say use a temperature gun from the hardware store I don’t know how else you would do it

poundofyourfinest said:

I was going to say use a temperature gun from the hardware store I don’t know how else you would do it

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Ok, sounds like just trust what i have (15 dollar IR gun from amazon). Wasnt sure if emissivity of leaves was far off what an average gun measures. I just know that you can spend thousands on other methods like FLIR to monitor leaf temp. Definitely not doing that, was just curious if theres something better tuned to the emissivity of leaves for not too much money.

DWCgrower406 said:

Ok, sounds like just trust what i have (15 dollar IR gun from amazon). Wasnt sure if emissivity of leaves was far off what an average gun measures. I just know that you can spend thousands on other methods like FLIR to monitor leaf temp. Definitely not doing that, was just curious if theres something better tuned to the emissivity of leaves for not too much money.

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I have a FLIR T620 IR camera that I barrowed form work (to check for tent leaks). It gives me comparable results to my IR grill thermometer, which ran about $25. Even if I go though the trouble of setting the emissivity to the plant leaves (0.97) It doesn't effect the reading much. You should be just fine.

Cpl. Cat said:

I have a FLIR T620 IR camera that I barrowed form work (to check for tent leaks). It gives me comparable results to my IR grill thermometer, which ran about $25. Even if I go though the trouble of setting the emissivity to the plant leaves (0.97) It doesn't effect the reading much. You should be just fine.

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Perfect, thats what i wanted to know right there. 0.97 emissivity is definitely close enough. I just remembered back when i was into nitro rc cars and i checked engine temp with IR, there was huge emissivity difference between clear aluminum and other finishes like powder coat. Not specifying emissivity gave huge error in that case. Sounds like no significant error in this case.