Leaf temps under LED/LEC/HPS

Nutria said:

@wietefras may I ask you what IR sensor module are you using ? or temperature camera, whatever you like it calling

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Lol, the people who sell these things call it plant temperature camera. Guess that sounds cooler then "IR thermometer"

If it's not mentioned in my Arduino experiments thread then I wouldn't know which one it was. It's been years sorry. Just any IR sensor would suffice though. They usually sell them in different beam angles, so you can fit that to your own needs (size of grow)

ok thank you anyway

I will probably get a AMG8833 and play with it

Rocket Soul said:

Thats really what i was looking for, but no CMH on the list.

Not very likely, they were under cmh for most of the veg. Its hard to up the nutrients as the extra nutes would likely build up salts in the coco. I have a feeling that what my friend is suffering from is "calmag" problems similar to those you get under leds, due to the plant not transpiring enough as his VPD seems low


I guess i could have been clearer in what im asking about. Been using this:
http://opennlabs.com/vpd/VPD_calculator.php

to try to calculate vpd. Its a really nifty resource as it allows for setting how much hotter or colder the leaf temp is, compared to ambient.

Weve measured left temp (1-2 below ambient), and got different values with both infrared/laser meters. Also the flir meter in the article above got much higher values on all light sources.

Is there anyway to figure out what would be the right value? Is there a way to figure out if a laser meter is consistently giving you high or low values?

What values would people use for for leaf temp of you were to try to figure out the vpd for HPS / CMH / LED? How much higher/lower would you rank your leaf temp?
And at what light levels, as a 400w hps wouldnt run as hot as 1000w hps?

Yeah, i know, lots of questions just hoping for some input. I used -1°C for leaf temp on the CMH (par 250) , got very low vpd on 22-24°C, 80RH.
Using +3°C for HPS 600w with same temp/rh gives pretty much perfect vpd.

What does everyone think?

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CMH and HPS contain both lot's of far-red which heats up the leafes to the same degree.
You should use +3 for both types of bulbs.
With warmwhite LED leaf temps are -3° less and with red/blue LED(without far-red) it's up to -5° less against ambient temps.

Randomblame said:

CMH and HPS contain both lot's of far-red which heats up the leafes to the same degree.
You should use +3 for both types of bulbs.
With warmwhite LED leaf temps are -3° less and with red/blue LED(without far-red) it's up to -5° less against ambient temps.

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That was my first feeling aswell, but the HPS dialed in environment simply did not work out. Maybe cause the actual wattage wasnt the same.
There are lots of opinions on this, did you read the article? :
https://www.blackdogled.com/lst

They quote quite differnt numnumbers although the relative difference between lights seems to be the same. I think you get different values depending on how you measure it.
But allways welcoming more opinions, thats why i itarted the tread.

Nutria said:

ok thank you anyway

I will probably get a AMG8833 and play with it

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Ah, with multiple sensors. That's even cooler perhaps. I used a simple single IR sensor.

I found which one I used. It was the Melexis MLX90614. This sensor comes in a lot of different forms like 10 or 35 degree beam angles.

Rocket Soul said:

That was my first feeling aswell, but the HPS dialed in environment simply did not work out. Maybe cause the actual wattage wasnt the same.
There are lots of opinions on this, did you read the article? :
https://www.blackdogled.com/lst

They quote quite differnt numnumbers although the relative difference between lights seems to be the same. I think you get different values depending on how you measure it.
But allways welcoming more opinions, thats why i itarted the tread.

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These is actually my own experiences and the experiences of others here.
With my old Osram Nav-T 600w HPS and a 1m2 tent I had for instance set a the target temperature to 25°C/77°F and had leaf temps of 27-28°C/80-82°F. However, to reach the same temperature with white LEDs I need 30°C/85°F ambient temps. This has often been mentioned here and is considered as generally accepted.

I would handle a CMH/LEC like an HPS and would go with 25°C as target ambient temperature and measure the temps across the canopy. CMH/LEC has a better spectrum and the especially the 4100°k has a lot more blue, but a huge part of the spectrum(~10%) is still above 700nm like with HPS.
Although I never had a CMH or LEC myself, I'm pretty sure the leaf temperatures are also rising 2-3° above ambient levels.

Dave455 said:

Flower dosage on MC ?

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Just flipped to flower, will ramp up to the recommended 6 grams/gallon. The recommended 4g/gallon for veg has worked beautifully, except the girl is going to explode the tent! So easy a caveman can do it, I proved that.

under 1000W of cobs usually in the range of +0,5-1°C over ambient, measured with thermocouple

wietefras said:

Yes temps are very important since a small change in leaf temp can give you big swings in VPD. If you look at thos blackdoge FLIR images you see how much leaf temperature van vary. Calibration and averaging out is very important.



Not directly from above. It should be at a "shallow" angle. Otherwise you risk looking through the plants to the (much colder) floor, Usually it says the spread of the sensor beam somewhere on the side of those IR temp sensors. Or otherwise in the specs. Try to adjust the distance so you get a sized area covered.

In greenhouses they measure quite large area's:
View attachment 4146971

They call it a 79 degree angle, but I would call that an 11 degree angle. It's a very shallow angle to the canopy.

I'm assuming this won't fit in your grow. It sure does not in mine. So I use a 45 degree angle. Not perfect, but I don't have the space to get it any more shallow. Otherwise I measure the walls.

Lower RH gives a higher VPD, more transpiration and therefore more Ca uptake. So yes, that could be the difference.

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Mine Pray at 79F/49RH

@Rocket Soul
Finally I was able to read the blackdog test about LST today, was not available yesterday.
IMO the LST test is a bit optimized to their own products because they choose a white light with blue/green weighted spectrum(see below, 40% 10000°k + 60% 2700°k, peak wavelength ~575nm).
A huge part of the green light heats up the LS in the same way far-red does.
A more red weighted spectrum with 10% 10000°k and 90% 2700°k would contain much less green and blue wavelength and should not heat up the leaves that much as under this 40/60% mix.
I think they deliberately chose such a spectrum to give their own lights an small edge.
A spectrum with less coolwhite has fewer "wasted" photons is used more efficiently and therefore doesn't heat up the LS so much. With a more red weighted spectrum I think the difference is only ~1° compared to their own, because there is still a bit far-red in warmwhite.
However, this is precisely the advantage of white light (keyword: EmersonEffect) because some additional far-red in the range around 730nm can increase the photosyntosis effectively (see attached paper).
From that paper, the blurple units profits more from additional far-red, because plants under white LED already benefit a bit from the far-red part. CRI90 contains almost twice as much far-red than CRI80 and in many tests growers report from better results, despite lower efficiency!
For me this is a confirmation and I now use a mix of CRI80 and 90 to further increase the far-red part and the dark red tones of my spectrum. I just finished my first run with a 3000°k CRI80/90 mix and got 505g from 10sft, 321w LED + 39w UVB reptile tube. Temp/hum. was set to 85°F/60% and LST were measured several times, always between 79-82,5°F/26-28°C.

Yeah, that's only 1,4g/w but still 50g/sft and I had some trouble because of too intense light(+60klx). I had to keep the distance at 12" in order to get effective UVB light(150-180μW/cm²), but the LED's would have been better 16-20“.
The 3ft. T5HO contains a lot "wasted wavelength" (12/30% UVB/A, 7000°k with lot of green) but it was only 39w and does not had a big impact, LST stayed in the same 26-28°C range.

1212ham said:

Just flipped to flower, will ramp up to the recommended 6 grams/gallon. The recommended 4g/gallon for veg has worked beautifully, except the girl is going to explode the tent! So easy a caveman can do it, I proved that.

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Finding 700 ppm range and 5 per gallon looks good. adding little Epsom and molasses also...