Why we should be running Higher Temps for LED lights

Something ive been wanting to bring up and discuss as a side topic in its own thread instead of jumbling it into the “Cheap LED Strips : A Viable Alternative” thread to avoid congestion.

So to the point when running LED lights we should be running higher temperatures than one might figure.

Reason being is the Leaf Surface Temperature of our plants is lower under LED lights than what it would be under say HPS even if the room temperature is exactly the same, reason for this is HPS throws out quite a bit of IR heat where as LED’s do not and with that you could easily see a 5C+/13F+ difference at the leaves.

This difference can make a considerable impact on the rate at which our plants transpire and there ability to cool themselves when exposed to high amount of light, and if one doesn’t know or consider this fact they will most likely experience slower growth than what they may be use to, so consider that and if you can grab leaf temps of your plants with an IR thermometer before you switch or consider bumping up your room temperatures past “older” recommended room temps to allow for greater growth.

Personally at the time of this posting i have my exhaust fan setpoints in the 31-32C region “88-90F” which for myself corresponds to leaf temperatures in the 28-30c range “82-86f” which works for me, different cultivars and or grow environments may warrant different setpoints though.

Obviously do your own experimentation for what works for you and totally feel free to share that information here so we can get a discussion going about it and working out some more ideal temps for LED growers.

Also to add some outside OG info, here is a great page by Blackdogled about Leaf Surface Temperatures with FLIR measurements under LED’s, MH and HPS to illustrate the points above.


And a pic grabbed from their site, so full credit to them and there work, i just added this as a pic for the oogles and not to get into discussion or nerd feast on comparable accuracy of light wattage vs observed photon density and the likes at sites measured and how close the comparisons are.


I thought of this and have run a reptile IR bulb fairly high in my tent to increase leaf surface temperature. It also helps trigger Emerson effect in theory.


Never even thought this was important. I’m not even sure how to raise my tent temp at the moment wonder how little I can run my fan.


spectrum_865d4009-95b3-4ebb-86fc-20152b065f3a_large rating

Light charts for an exoterra IR bulb and for Mars hydro ts1000


What temperature do you like to maintain during flower?

For veg I struggle to get high temps and do notice slow growth and always run into Mg/P issues.

Once I flip i like to maintain 25-26deg with 45% humidity and my plants love it.


@anon93244739 Cool that does add alot of IR Light/energy/heat, more my purpose of this thread was not the addition of IR to supplement led light source if one “feels or desires” that they need it but more that just the plants will experience lower leaf temps under LED than what they would under other sources of light and in order to compensate instead of addition that one should maybe adjust there room temps to compensate.


That was my first reason to add it actually ( raising surface temps) if you use it during veg they stretch like hell though. I at least have to fight for 70° this time of year. Realizing how much FR not just IR is produced is an added benefit IMO.


As posted my cabinets air temps range in the 31-32c area which is 28-30c at the leaves with depending RH percentages in the 55-70% range.

And my exhaust fan sips air and im fortunate to have it able to be running off temp and humidity setpoints, its usually cycles on and off at its lowest setting for say 20-30secs on then off again for 80-100 secs which allows it to keep its heat in though when “night” comes humidity usually spikes due to the loss of that light heat so then my fan usually runs solid to bring that humidity down till lights come back on, makes for a colder night temp but has been working.


Excellent topic. Growmau always said to run 84°F with LEDs, so that’s my setpoint. Each light will be slightly different, so getting a cheap IR thermometer and measuring for yourself is best. I’m getting a leaf surface temperature of about 77°F :+1::seedling:


I’ve been guilty of trying to give my plants too much light. I used to fight for every inch from the bulb (where it would have been much warmer) and now I just set it at 16” and let it go with no obvious negative effects. But I guess in this instance closer would be too much light AND too hot.

If I had absolute control over my grow space I would likely run on the hot side but there are swings beyond my control and I either run hot or cold depending on the day. Even though the LED runs cooler than an HPS mine still kicks out a fair amount of heat. Maybe it’s just not very efficient :slight_smile:


I found if i keep air temp between 26 and 30C all is usually well. Above 30 and humidity drops so they transpire more to compensate which can cause bud rot. Growth starts slowing down too as temps rise above the low 30s


Thats basically how my boxes are ran. I use the ac infinity t6. After reading this I may set the temps higher now.


Excellent point!

I have been checking my leaf temps (1st grow under the new lights) & I noticed they were running 3~6C below ambient. (depending on watering)

Is it safe to assume that the delta between leaf and ambient temperatures in veg are similar in flower?



This is useful info, so many have been growing with glowing bulbs and are switching.
I was still doing the max 25-26C in shade , being winter I am way off using LEDs, gotta get on that.
Bigbudsmag article recommends 72-82F(22.2C-27.7C) as acceptable leaf surface temperature.
Now wheres that IR thermometer.

EDIT: man, my LST was 20C with 22C room temp. Going to need a reptile bulb, too much humidity with reduced ventilation.


So I kicked mine up 5degress fahrenheit and the plants seem to be responding well. Much perkier. Went from 82 to 87.


This is perfect timeing! I’m just about to install my AC T4 exhaust fan. So I should set the fan to trigger when it reaches 89-90F? Then what humidity should I set the fan to trigger at? If I’m venting for humidity, would that offset the desired temp too much and just chasing my tail? I lost my first crop to bud rot since I didn’t vent it at night, just had the fans inside recirculating.


Good point and interesting to think about. You could probably run the VPD formulas to estimate (or simulate) the transpiration differences … actually using the leaf temperatures in the formulas. The simplified versions consider leaf temps to be at the same temperature as the surroundings.

What’s cool, also, noting the leaf temps one could diagnose when the plant is getting too much light or is under stress as it sheds the excess energy as heat and/or as it shuts down the stomata.


Any good suggestions for increasing room temp?


I would just get it up and running with basic temp and rh, watch and see what happens. Pretty easy to dial the ac infinity in.


I try to run leaf temp 3 degree cooler than room temp my plants like it on the warm side average day temp 86/88 f cool nights low 60’s lots of air movement . Excellent topic @Mr.Sparkle vpd is important as watering .